The sensitivity for the tilted pinholes can be given as follows: where dSeff is the sensitivity effective pinhole diameter corrected for penetration effect (49), n is a normal vector coincident with the tilted pinhole axis, (x1,y1,z1) is the pinhole aperture center and (x2,y2,z2) is an arbitrary point along the pinhole axis. The distance from the detector surface to the CFOV is 30 cm and 27 cm for brain and cardiac imaging, respectively. The acceptance angle of the central pinhole is 53 and perpendicular to the crystal surface, while the acceptance angle of the outer holes is 45 and their longitudinal axes converge inward at 26.5, forming a conically tipped cylindrical FOV 12.7 cm in diameter. The most commonly used materials for clinical pinhole SPECT collimator are tungsten (W) and lead (Pb) due to their high stopping power and economic considerations. The researchers fixed the target spatial resolution at 6 mm in the CFOV and then maximized the volume sensitivity by varying the collimator radius, aperture size and number of loftholes. SPECT is based on the detection of single gamma rays emitted from an administered radiotracer that is distributed in the patients body. Nine detectors are placed along the transaxial direction covering 180. With permission of MILabs B.V. Utrecht, The Netherlands. Arrows indicate the rotation of the whole scanner (including detectors, collimators and actuators) to enable acquisitions of different views [courtesy of van Roosmalen et al. (87) for DC imaging studies. Beekman FJ, van der Have F, Vastenhouw B, van der Linden AJ, van Rijk PP, Burbach JP, Smidt MP. Evaluation of a multi-pinhole collimator for imaging small animals with different sizes. Vaissier et al.
DC-SPECT was proposed and evaluated by Uzun Ozsahin et al. An adaptation to this method that also allows a circular pinhole aperture but provides rectangular projections to avoid multiplexing is the use of a lofthole proposed by Deprez et al. A new method of multiplanar emission tomography using a seven pinhole collimator and an Anger scintillation camera. A summary of the characteristics for the different clinical MPH SPECT systems mentioned is listed in Table 1. (36) found that the MPH SPECT for small FOV imaging is able to achieve high detection efficiency without much deterioration in resolution, as MPH provided more angular sampling compared to conventional LEHR and single pinhole collimator. The Discovery NM 530c is a commercially available system dedicated for MPI, developed by GE Healthcare, Haifa, Israel (4). A planar cut through the central detector and two peripheral detectors from a seven-pinhole pod; (B) a planar cut through the central pod and one peripheral pod; (C) 3D rendering view of the 49-pinhole configuration. where Pmultiplexing and Pnon-zero represent the number of pixels with multiplexing in the projection and number of pixels with non-zero value in the projection, respectively. See: https://creativecommons.org/licenses/by-nc-nd/4.0/. The other authors have no conflicts of interest to declare. Van Audenhaege K, Vanhove C, Vandenberghe S, Van Holen R. The evaluation of data completeness and image quality in multiplexing multi-pinhole SPECT. U-SPECT systems (50,51) employ dual stage collimation to effectively achieve non-multiplexing, i.e., non-overlapping projections (Figure 4). Each pinhole has an aperture of 5.1 mm in diameter. Several research groups have shown that multiplexing may misplace the activity in the reconstruction (56-59). Specifications such as pinhole aperture size and number of pinholes open can be adjusted based on individual patients and applications (92). For (E), lofthole, dual stage collimation and rectangular pinhole, there is 100% usage with no multiplexing, while truncation may or may not be present depending on the magnification of the spherical phantom. Another advantage of MPH collimators is the large reduction in collimator penetration versus parallel-, cone- or fan-beam collimators. This design consists of three hexagonal detector rings: caudal ring with 9 detectors, middle ring with 9 detectors, and quasi-vertex ring with 5 detectors. (86). Projections from the pinhole collimator may suffer more from the DOI effect compared to other collimators when the incident angles are large. On the other hand, without changing magnification, more pinholes could be packed to further improve the detection efficiency at the same spatial resolution. VECTor: a preclinical imaging system for simultaneous submillimeter SPECT and PET. Left: LaPET scanner with a collimator insert. Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at http://dx.doi.org/10.21037/qims-19-1036). Dashed lines indicate the pinhole axes, which converge on a line 40 mm from the collimator. Sabet H, Backberg L, Uzun Ozsahin D, El Fakhri G. Novel laser processed CsI:Tl detector for SPECT. Record, 2017. Conversely, collimators with smaller holes provide better spatial resolution with lower sensitivity. This technique requires fewer acquisition steps compared to other stationary small animal SPECT systems with focusing MPH collimators, which need to shift the animal bed for 5 to 80 bed positions for a total body mouse scan depending on the collimator used. The 45 detector modules are arranged in 3 rows in the proposed dynamic MPH cardiac SPECT design [courtesy of Uzun Ozsahin et al. Physical and clinical evaluation of high-resolution thyroid pinhole tomography. Feng B, Chen M, Bai B, Smith AM, Austin DW, Mintzer RA, Osborne D, Gregor J. Their optimization results showed that the volumetric sensitivity (0.016%) was 2.5 times lower than the sensitivity of a dual-head system with LEHR collimator, while the spatial resolution was improved, with the ability to reconstruct 4 mm rods. Preliminary Investigation of Axial and Angular Sampling in Multi-Pinhole AdaptiSPECT-C with XCAT Phantoms. (33)]. (D) Perpendicular cross-section through collimator-detector set-up showing the pinhole geometry. Schematic sketch of NFRCDC, FOCDC, and FRCDC knife-edge pinhole designs [courtesy of Bal et al. This increasing demand has led to the development of several dedicated commercial MPH SPECT scanners for cardiac applications that are currently on the market, with various research prototypes developed or being investigated. (97). (81)]. Received 2020 Jul 8; Accepted 2020 Jul 30. Thus, the reconstruction procedure alternates between two different iterative processes, i.e., first, estimating separated projection data for each pinhole and second, using the separated projection estimates to reconstruct an image. Goorden MC, van der Have F, Kreuger R, Ramakers RM, Vastenhouw B, Burbach JP, Booij J, Molthoff CF, Beekman FJ. MPH collimators are tilted to cover the FOV. They found that increasing the channel height resulted in a higher spatial resolution but also a rapid decrease in sensitivity for off-axis sources. The peak sensitivity can reach 0.37% for the focusing mode with a restricted FOV of 27 mm. The increasing clinical need for dedicated diagnostic systems with improved performance for imaging specific organs, e.g., the heart and brain, has led to the development of single photon emission computed tomography (SPECT) systems with better resolution, sensitivity and throughput (1-12) than standard general-purpose SPECT systems. Since multiplexing allows the projection size to be larger than that of the non-multiplexing design, it could potentially allow a larger magnification factor to improve spatial resolution and increase the sensitivity if the larger magnification is obtained by bringing the pinholes closer to the source. Mok GSP, Tsui BMW, Wang Y, Du Y, Segars WP, Frey EC. SPECT/CT: an update on technological developments and clinical applications. The degree of multiplexing is more in this 5-pinhole case, yet the ghost artifacts are not observed, probably due to the added central projection providing more information for image reconstruction to avoid the null space problem. The reconstructed images showed that increased axial sampling by combined reconstruction of acquisitions from solely the base apertures and then solely the two axially spaced apertures for Defrise phantom resulted in an increase in the number of disks resolved from 6 to 13 (all).
A user interface that employs three optical cameras is used to select the scan region to maximize the focus capabilities (83). Gullberg GT, Zeng GL, Datz FL, Christian PE, Tung CH, Morgan HT. Evaluation of stationary and semi-stationary acquisitions in a dual-head multi-pinhole collimator for myocardial perfusion SPECT. Figure 6 illustrates the MPH multiplexing with a rectangular detector. The detectors are arranged in three rows perpendicular to the axial direction. Systematic review of the diagnostic utility of SPECT imaging in dementia. The ratio of utilized area to total area of detector is ~52% and ~79% for (A) single pinhole and (B) six-pinhole collimators with no multiplexing, respectively. Right: representation of robotic SPECT imaging for a patient in position for radiation therapy. Note that all the pinholes are tilted towards the CFOV. European Patent Application EP2073039. Ono M, Watanabe H, Kitada A, Matsumura K, Ihara M, Saji H. Highly selective tau-SPECT imaging probes for detection of neurofibrillary tangles in Alzheimer's disease. FRCDC has the least penetration owing to its smallest acceptance angle under the same FOV, making it the best for high energy applications. He is founder, shareholder, and part time CEO of MILabs B.V, a company that develops pinhole PET and SPECT systems like the U-SPECT and G-SPECT-I scanners that were addressed in the present paper. Huang et al.
Design of a dual-resolution collimator for preclinical cardiac SPECT with a stationary triple-detector system. However, modelling the sensitivity and resolution of the tilted pinholes is challenging and conventional formulas cannot be applied because of the position-dependent penetration length and DOI of the tilted aperture (as detailed in later section).
All 54 pinholes distributed over three rings are focused on the complete data volume [CDV: the spherical object shown (A) in the FOV]. (33) used seven pinholes to obtain simultaneous projections of an emission source onto seven independent regions of an Anger scintillation camera. Quantitative Imaging in Medicine and Surgery, https://creativecommons.org/licenses/by-nc-nd/4.0/, https://srd.nist.gov/NSRDS/NSRDS-NBS29.pdf, Multi-pinhole cardiac SPECT (12-pinhole & 14-pinhole). Thus, clinical MPH SPECT systems are currently being developed for brain and cardiac imaging for the most part, which target relatively small or medium sized VOIs that are suitable for pinhole imaging. *, body collimator is under characterization. Chen et al. Advanced image reconstruction algorithms such as statistical reconstruction methods that incorporate corrections for various image degradation factors, e.g., attenuation, object scatter, patient motion, partial volume effect and collimator-detector response functions that include geometric response function, intrinsic response function, septal penetration, septal scatter function, as well as multiplexing and the DOI effect mentioned in the previous sections, are essential for pursuing absolute quantitation in MPH SPECT (69). Based on the same resolution with the LEHR collimator, the total sensitivity is 0.035%, which is 2.5 times better than LEHR collimator. Onboard functional and molecular imaging: A design investigation for robotic multipinhole SPECT. One of the first MPH collimators was developed in 1978 when Vogel et al. Performance analysis of a high-sensitivity multi-pinhole cardiac SPECT system with hemi-ellipsoid detectors. where n is the number of pinholes. Mozley PD, Schneider JS, Acton PD, Plssl K, Stern MB, Siderowf A, Leopold NA, Li PY, Alavi A, Kung HF. Wernick MN, Aarsvold JN. An MPH MBT system was proposed by van Roosmalen et al. A 49-pinhole SPECT system was designed and investigated by simulations for use as a computer-aided robotic system for head, breast, thorax, arms and legs imaging in radiation therapy (Figure 20) by Bowsher et al. Beekman FJ, van der Have F, Goorden MC, Vaissier PEB, van Roosmalen J, During H. G-SPECT-I: a full ring high sensitivity and ultra-fast clinical molecular imaging system with <3mm resolution. The compression process and scanner geometry for MBT. Besides superior spatial resolution, another advantage of G-SPECT-I is its fast scanning speed with sub-second time frames in the case of focused imaging. The potential for mixed multiplexed and non-multiplexed data to improve the reconstruction quality of a multi-slitslat collimator SPECT system. The pendant breast is compressed by transparent compression plates and imaged by two tungsten collimators with 10 mm thickness, each with 63 pinholes (Figure 21). Careers.
Bae et al. The role of DAT-SPECT in movement disorders. The six peripheral pinholes are in a hexagonal pattern at a distance of 6.35 cm from the central pinhole, which is positioned at the center of the hexagon. Metzler SD, Moore SC, Park MA, Design of a new small-animal SPECT system based on rectangular pinhole aperture. To correct this geometric change, a virtual object plane parallel to the tilted aperture plane was set such that the geometric sensitivity and penetration path length in the conventional equation can be applied with respect to this virtual object plane. 8600 Rockville Pike The site is secure. An investigation of inconsistent projections and artefacts in multi-pinhole SPECT with axially aligned pinholes. Accessibility Some research groups are working on the elimination of the DOI effect for MPH SPECT. An official website of the United States government. GATE: a simulation toolkit for PET and SPECT. The pinhole acceptance angle is 32.5 and peripheral pods are tilted towards the central pod by 16.25. An Efficient Sensitivity Calculation of Tilted Apertures for Preclinical Multi-pinhole SPECT. For (C), there is ~93% usage with ~33% multiplexing and no truncation. Derivation of system matrix from simulation data for an animal SPECT with slit-slat collimator. vs. 2.97 cm1 at 364 keV (39). Proposed small organ MPH collimator [courtesy of Bae et al. However, obtaining an experimental and Monte Carlo based system response matrix is time consuming even when interpolations and variance reduction methods (74,75), e.g., force detection techniques, are applied. A collimator is made of high-atomic number and high-density materials such as tungsten and lead which highly absorb incident photons except those traveling through holes of known angulation. Clinical utility of dopamine transporter single photon emission CT (DaT-SPECT) with (123I) ioflupane in diagnosis of parkinsonian syndromes. Van Audenhaege et al. (B) After the scan volume selection, the collimator plates and gamma detectors move into scanning position (arrows). National Library of Medicine The performance of W and DU-238 was found to be similar, while pinholes with 23 mm aperture sizes had the best results in terms of signal-to-noise ratio (SNR). Evaluation of early-stage Parkinsons disease with 99mTc-TRODAT-1 imaging. Lead and tungsten pinhole inserts for I-131 SPECT tumor imaging: experimental measurements and photon transport simulations. Bal et al. Quantification of the multiplexing effects in multi-pinhole small animal SPECT: a simulation study. Bowsher J, Yan S, Roper J, Giles W, Yin FF. At the focal point of the apertures the spatial resolution and sensitivity of the system are 4.8 mm and 973.0 cps/MBq, respectively. GEANT4 application for tomographic emission (GATE) (90) simulations for the four scanners were performed to evaluate the systems in terms of sensitivity and spatial resolution by using a point source placed at the CFOV. Academic Press, 2004. A full-ring multi-lofthole collimator, which consists of a tungsten ring with loftholes, is mounted on the system with a shutter mechanism that controls the projection overlapping and also provides complete angular sampling without the need for rotational acquisition. The adverse effect of multiplexing can also be corrected during iterative image reconstruction (62). SPECT/CT in tumor imaging: technical aspects and clinical applications. [5]. (8) designed a 14-pinhole cardiac collimator based on a target resolution of 1 cm, FOV of 20 cm and H-mode rotational acquisition for a clinical SPECT scanner by maximizing the sensitivity. The smallest diameter collimator contains 54 pinholes with a bore diameter of 398 mm. They found that at least five pinholes are required to adequately reconstruct the point sources, and FWHMs of the MPH collimators are smaller than that of the parallel-hole collimator, i.e., ~911 mm (depending on the number of the pinholes) versus 12 mm. Another aperture design that uses square- or rectangular-pinholes with a square or rectangular FOV was proposed by Metzler et al.
Bocher M, Blevis IM, Tsukerman L, Shrem Y, Kovalski G, Volokh L. A fast cardiac gamma camera with dynamic SPECT capabilities: design, system validation and future potential. Effect of overlapping projections on reconstruction image quality in multipinhole SPECT. These two iterative steps are repeated until the multiplexing artifacts are considered to be eliminated or adequately reduced. Hubbell JH. For imaging smaller objects than the detector (e.g., organs or tumors), the trade-off between spatial resolution and sensitivity compared to a conventional parallel-hole collimator can be improved upon with the use of converging collimators for organ-specific SPECT applications (31). Investigation of imaging properties for submillimeter rectangular pinholes. In (D), there is 100% usage with ~38% multiplexing and truncation. The pinholes were located as shown in Figure 19 and all of them were tilted towards the CFOV. The ring is formed by 9 large FOV cameras using 595 mm 472 mm NaI (Tl) scintillation crystals. Focused pinhole gamma detection device. For the brain phantom, the image quality improves as the number of the pinholes increases and at least eight pinholes are required to generate images without significant artifacts. Bhusal et al. (C) Comparison of resolution of G-SPECT-I equipped with a 38 cm collimator with a dual head Siemens Symbia system at equal scan time and equal dose based on physical experiments (with permission of MILabs B.V. Utrecht, The Netherlands). Aperture-to-detector distance was set to 12 cm. Lyon, France: IEEE Nuclear Science Symposium and Medical Imaging Conference Record, 2018. (7) proposed the placement of an MPH collimator on one head of a SPECT system and a fan-beam collimator on the other head (Figure 15). They evaluated 3 to 12 knife-edge pinholes for each camera with no multiplexing (Figure 24). (A) G-SPECT-I system with three optical cameras and a user interface for volume-of-interest (VOI) selection; (B) multi-pinhole collimator of G-SPECT-I system. Single photon emission computed tomography (SPECT) is an important imaging modality for various applications in nuclear medicine. As shown in Figure 8, a low number of pinholes in a regular arrangement combined with multiplexing may result in ghost artifacts, i.e., for 4-pinhole in this case. Technical considerations such as pinhole aperture design, effect of multiplexing, sampling and depth of interaction (DOI) are firstly presented in the next section. Beekman FJ, inventor; MILabs BV, assignee. [2]. Since then MPH collimation was investigated and applied more and more often for clinical applications.
Cardiovascular disease is the greatest cause of mortality and morbidity in the world and SPECT is one of the most established imaging methods to assess myocardial perfusion. Compared to simple analytical reconstruction methods such as filtered back-projection, statistical reconstruction methods can incorporate the random nature of photon detection and allow compensation of various image quality degradation effects in the acquisition process via accurate system matrix modelling (70). Projections of an XCAT phantom representing a female patient in supine position were simulated. Monte Carlo simulations of a digital mouse phantom with different numbers of pinholes. (B) Photograph of one of the many identical platinumiridium inserts. 52nd Annual Meeting of the Society of Nuclear Medicine, 2005.
Moore SC, Cervo M, Metzler SD, Udias JM, Herraiz JL. Klein WP, Barrett H, Pang IW, Patton DD, Rogulski MM, Sain J, Smith W. FASTSPECT: electrical and mechanical design of a high-resolution dynamic SPECT imager. Jaszczak RJ, Li J, Wang H, Zalutsky MR, Coleman RE. The results showed that the proposed system has a spatial resolution of 10.0 mm and a sensitivity of 0.081%, while they were 20.1 mm and 0.084%, 15.0 mm and 0.049%, 15.2 mm and 0.011% for the D-SPECT, GE Discovery NM 530c and conventional dual head GE Infinia, respectively. On the other hand, sensitivity, which is also spatially variant, is the ratio of the detected photons to the emitted photons and can be expressed as detected percentage or as cps/MBq (SI unit of radioactivity). Both designs have a better performance than the LEHR collimator, which has a resolution of 12 mm and sensitivity of 0.010%. Left: experimental setup of the 9-pinhole MPI SPECT system with a torso phantom. Lead shielding was used inside the collimator to prevent multiplexing of the pinhole projections. Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). During this process, determination of the incident angle of gamma-photons on the detector is crucial. Developing an accurate mathematical model of the sensitivity and resolution profile of the keel-edge collimator is challenging. This algorithm estimates both the values of all image voxels, and the de-multiplexed projection data from each of the pinholes. (87)]. In this way the incident angle of the detected gamma-rays is determined. Shown are the 2 cm thick aperture plate with a single aperture per detector and the 23 hexagonal detectors (courtesy of Dr. Kesava S. Kalluri). In their designs, the patient lies prone on a specially designed bed with the scanner underneath. [1] (43). A sample 9-pinhole collimator (MPGP) mounted on a clinical SPECT scanner. Xia D, Moore SC, Park MA, Cervo M, Metzler SD. Experimental evaluation of a multi-pinhole collimator for a small organ by using a small-field-of-view gamma camera. (10) designed and evaluated two MPH collimators for brain SPECT to image cerebral blood flow and striatum (Figure 17) based on a GE Inifinia Hawkeye scanner. FOIA Monte Carlo calculations in nuclear medicine: Applications in diagnostic imaging, second edition. They assessed the feasibility of maneuvering the SPECT collimator system around the patient in position for radiation therapy, allowing an unrestricted therapy procedure. The SNR (defined by mean/standard deviation) of MPH collimators was found to be much worse compared to that of the parallel-hole collimator, i.e., 10 versus 60. Deprez K, Pato LR, Vandenberghe S, Van Holen R. Characterization of a SPECT pinhole collimator for optimal detector usage (the lofthole). The ROR is set to 167 mm to provide a FOV of 20 cm to accommodate the patients head, without touching the patients shoulder. Korevaar MA, Heemskerk JW, Beekman FJ. Nguyen MP, Goorden MC, Kamphuis C, Beekman FJ. The pinhole diameter was defined as 3 mm, with a collimator plate thickness of 10 mm. Measurement of absolute myocardial blood flow in humans using dynamic cardiac SPECT and 99mTc-tetrofosmin: Method and validation. The knife-edge pinholes have an acceptance angle of 42 and a diameter of 2.7 mm. Shrestha U, Sciammarella M, Alhassen F, Yeghiazarians Y, Ellin J, Verdin E, Boyle A, Seo Y, Botvinick EH, Gullberg GT. Lyon, France: 2000 IEEE Nuclear Science Symposium. Busca et al. The MPH collimator provides high resolution and sensitivity for imaging the striatal region and the fan beam collimator provides lower resolution but complete sampling of the brain. Spatial resolution was found to be 1.0 cm at 12.7 cm from the pinhole plate and the system sensitivity was found to be 750 cps/MBq at 11.5 cm from the pinhole plate (76). Wang Y. (64) proposed an MPH SPECT system for MPI to increase the sensitivity by 5-fold while maintaining the same image quality compared to a conventional rotational SPECT system with a low-energy general-purpose (LEGP) parallel hole collimator. PMC legacy view For example, the heart or the brain can be imaged much more efficiently by fan beam, cone beam or focused pinhole collimators, which can result in better trade-off in spatial resolution and sensitivity (32). Phys Med Biol 2009;54:N267-72.
In: Proceedings of IEEE NSS-MIC, 2015. Molecular breast imaging using a fully tomographic stationary clinical cardiac SPECT scanner: a phantom study. In: Matsuda H, Asada T, Tokumaru A. The preliminary prototype design of AdaptiSPECT-C together with a cropped XCAT phantom positioned inside. The first one is a two-sphere phantom comprised of two spherical sources with a diameter of 5 mm, one located at the CFOV and the other located 20 mm offset from the CFOV. (85). The diameter of each rod is 5 mm. The system is based on simultaneous acquisitions of multiple projections from multiple detectors where each one is coupled with an individual pinhole (Figure 22). Several strategies have been attempted to further improve the detection efficiency in MPH SPECT (30). Furthermore, Korevaar et al. Effects of pinhole material and aperture size on lesion contrast and SNR breast SPECT. Accomplishing this for SPECT/MRI is still being researched for clinical brain imaging (98-100).
DC-SPECT was proposed and evaluated by Uzun Ozsahin et al. An adaptation to this method that also allows a circular pinhole aperture but provides rectangular projections to avoid multiplexing is the use of a lofthole proposed by Deprez et al. A new method of multiplanar emission tomography using a seven pinhole collimator and an Anger scintillation camera. A summary of the characteristics for the different clinical MPH SPECT systems mentioned is listed in Table 1. (36) found that the MPH SPECT for small FOV imaging is able to achieve high detection efficiency without much deterioration in resolution, as MPH provided more angular sampling compared to conventional LEHR and single pinhole collimator. The Discovery NM 530c is a commercially available system dedicated for MPI, developed by GE Healthcare, Haifa, Israel (4). A planar cut through the central detector and two peripheral detectors from a seven-pinhole pod; (B) a planar cut through the central pod and one peripheral pod; (C) 3D rendering view of the 49-pinhole configuration. where Pmultiplexing and Pnon-zero represent the number of pixels with multiplexing in the projection and number of pixels with non-zero value in the projection, respectively. See: https://creativecommons.org/licenses/by-nc-nd/4.0/. The other authors have no conflicts of interest to declare. Van Audenhaege K, Vanhove C, Vandenberghe S, Van Holen R. The evaluation of data completeness and image quality in multiplexing multi-pinhole SPECT. U-SPECT systems (50,51) employ dual stage collimation to effectively achieve non-multiplexing, i.e., non-overlapping projections (Figure 4). Each pinhole has an aperture of 5.1 mm in diameter. Several research groups have shown that multiplexing may misplace the activity in the reconstruction (56-59). Specifications such as pinhole aperture size and number of pinholes open can be adjusted based on individual patients and applications (92). For (E), lofthole, dual stage collimation and rectangular pinhole, there is 100% usage with no multiplexing, while truncation may or may not be present depending on the magnification of the spherical phantom. Another advantage of MPH collimators is the large reduction in collimator penetration versus parallel-, cone- or fan-beam collimators. This design consists of three hexagonal detector rings: caudal ring with 9 detectors, middle ring with 9 detectors, and quasi-vertex ring with 5 detectors. (86). Projections from the pinhole collimator may suffer more from the DOI effect compared to other collimators when the incident angles are large. On the other hand, without changing magnification, more pinholes could be packed to further improve the detection efficiency at the same spatial resolution. VECTor: a preclinical imaging system for simultaneous submillimeter SPECT and PET. Left: LaPET scanner with a collimator insert. Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at http://dx.doi.org/10.21037/qims-19-1036). Dashed lines indicate the pinhole axes, which converge on a line 40 mm from the collimator. Sabet H, Backberg L, Uzun Ozsahin D, El Fakhri G. Novel laser processed CsI:Tl detector for SPECT. Record, 2017. Conversely, collimators with smaller holes provide better spatial resolution with lower sensitivity. This technique requires fewer acquisition steps compared to other stationary small animal SPECT systems with focusing MPH collimators, which need to shift the animal bed for 5 to 80 bed positions for a total body mouse scan depending on the collimator used. The 45 detector modules are arranged in 3 rows in the proposed dynamic MPH cardiac SPECT design [courtesy of Uzun Ozsahin et al. Physical and clinical evaluation of high-resolution thyroid pinhole tomography. Feng B, Chen M, Bai B, Smith AM, Austin DW, Mintzer RA, Osborne D, Gregor J. Their optimization results showed that the volumetric sensitivity (0.016%) was 2.5 times lower than the sensitivity of a dual-head system with LEHR collimator, while the spatial resolution was improved, with the ability to reconstruct 4 mm rods. Preliminary Investigation of Axial and Angular Sampling in Multi-Pinhole AdaptiSPECT-C with XCAT Phantoms. (33)]. (D) Perpendicular cross-section through collimator-detector set-up showing the pinhole geometry. Schematic sketch of NFRCDC, FOCDC, and FRCDC knife-edge pinhole designs [courtesy of Bal et al. This increasing demand has led to the development of several dedicated commercial MPH SPECT scanners for cardiac applications that are currently on the market, with various research prototypes developed or being investigated. (97). (81)]. Received 2020 Jul 8; Accepted 2020 Jul 30. Thus, the reconstruction procedure alternates between two different iterative processes, i.e., first, estimating separated projection data for each pinhole and second, using the separated projection estimates to reconstruct an image. Goorden MC, van der Have F, Kreuger R, Ramakers RM, Vastenhouw B, Burbach JP, Booij J, Molthoff CF, Beekman FJ. MPH collimators are tilted to cover the FOV. They found that increasing the channel height resulted in a higher spatial resolution but also a rapid decrease in sensitivity for off-axis sources. The peak sensitivity can reach 0.37% for the focusing mode with a restricted FOV of 27 mm. The increasing clinical need for dedicated diagnostic systems with improved performance for imaging specific organs, e.g., the heart and brain, has led to the development of single photon emission computed tomography (SPECT) systems with better resolution, sensitivity and throughput (1-12) than standard general-purpose SPECT systems. Since multiplexing allows the projection size to be larger than that of the non-multiplexing design, it could potentially allow a larger magnification factor to improve spatial resolution and increase the sensitivity if the larger magnification is obtained by bringing the pinholes closer to the source. Mok GSP, Tsui BMW, Wang Y, Du Y, Segars WP, Frey EC. SPECT/CT: an update on technological developments and clinical applications. The degree of multiplexing is more in this 5-pinhole case, yet the ghost artifacts are not observed, probably due to the added central projection providing more information for image reconstruction to avoid the null space problem. The reconstructed images showed that increased axial sampling by combined reconstruction of acquisitions from solely the base apertures and then solely the two axially spaced apertures for Defrise phantom resulted in an increase in the number of disks resolved from 6 to 13 (all).
A user interface that employs three optical cameras is used to select the scan region to maximize the focus capabilities (83). Gullberg GT, Zeng GL, Datz FL, Christian PE, Tung CH, Morgan HT. Evaluation of stationary and semi-stationary acquisitions in a dual-head multi-pinhole collimator for myocardial perfusion SPECT. Figure 6 illustrates the MPH multiplexing with a rectangular detector. The detectors are arranged in three rows perpendicular to the axial direction. Systematic review of the diagnostic utility of SPECT imaging in dementia. The ratio of utilized area to total area of detector is ~52% and ~79% for (A) single pinhole and (B) six-pinhole collimators with no multiplexing, respectively. Right: representation of robotic SPECT imaging for a patient in position for radiation therapy. Note that all the pinholes are tilted towards the CFOV. European Patent Application EP2073039. Ono M, Watanabe H, Kitada A, Matsumura K, Ihara M, Saji H. Highly selective tau-SPECT imaging probes for detection of neurofibrillary tangles in Alzheimer's disease. FRCDC has the least penetration owing to its smallest acceptance angle under the same FOV, making it the best for high energy applications. He is founder, shareholder, and part time CEO of MILabs B.V, a company that develops pinhole PET and SPECT systems like the U-SPECT and G-SPECT-I scanners that were addressed in the present paper. Huang et al. Design of a dual-resolution collimator for preclinical cardiac SPECT with a stationary triple-detector system. However, modelling the sensitivity and resolution of the tilted pinholes is challenging and conventional formulas cannot be applied because of the position-dependent penetration length and DOI of the tilted aperture (as detailed in later section).
All 54 pinholes distributed over three rings are focused on the complete data volume [CDV: the spherical object shown (A) in the FOV]. (33) used seven pinholes to obtain simultaneous projections of an emission source onto seven independent regions of an Anger scintillation camera. Quantitative Imaging in Medicine and Surgery, https://creativecommons.org/licenses/by-nc-nd/4.0/, https://srd.nist.gov/NSRDS/NSRDS-NBS29.pdf, Multi-pinhole cardiac SPECT (12-pinhole & 14-pinhole). Thus, clinical MPH SPECT systems are currently being developed for brain and cardiac imaging for the most part, which target relatively small or medium sized VOIs that are suitable for pinhole imaging. *, body collimator is under characterization. Chen et al. Advanced image reconstruction algorithms such as statistical reconstruction methods that incorporate corrections for various image degradation factors, e.g., attenuation, object scatter, patient motion, partial volume effect and collimator-detector response functions that include geometric response function, intrinsic response function, septal penetration, septal scatter function, as well as multiplexing and the DOI effect mentioned in the previous sections, are essential for pursuing absolute quantitation in MPH SPECT (69). Based on the same resolution with the LEHR collimator, the total sensitivity is 0.035%, which is 2.5 times better than LEHR collimator. Onboard functional and molecular imaging: A design investigation for robotic multipinhole SPECT. One of the first MPH collimators was developed in 1978 when Vogel et al. Performance analysis of a high-sensitivity multi-pinhole cardiac SPECT system with hemi-ellipsoid detectors. where n is the number of pinholes. Mozley PD, Schneider JS, Acton PD, Plssl K, Stern MB, Siderowf A, Leopold NA, Li PY, Alavi A, Kung HF. Wernick MN, Aarsvold JN. An MPH MBT system was proposed by van Roosmalen et al. A 49-pinhole SPECT system was designed and investigated by simulations for use as a computer-aided robotic system for head, breast, thorax, arms and legs imaging in radiation therapy (Figure 20) by Bowsher et al. Beekman FJ, van der Have F, Goorden MC, Vaissier PEB, van Roosmalen J, During H. G-SPECT-I: a full ring high sensitivity and ultra-fast clinical molecular imaging system with <3mm resolution. The compression process and scanner geometry for MBT. Besides superior spatial resolution, another advantage of G-SPECT-I is its fast scanning speed with sub-second time frames in the case of focused imaging. The potential for mixed multiplexed and non-multiplexed data to improve the reconstruction quality of a multi-slitslat collimator SPECT system. The pendant breast is compressed by transparent compression plates and imaged by two tungsten collimators with 10 mm thickness, each with 63 pinholes (Figure 21). Careers. Bae et al. The role of DAT-SPECT in movement disorders. The six peripheral pinholes are in a hexagonal pattern at a distance of 6.35 cm from the central pinhole, which is positioned at the center of the hexagon. Metzler SD, Moore SC, Park MA, Design of a new small-animal SPECT system based on rectangular pinhole aperture. To correct this geometric change, a virtual object plane parallel to the tilted aperture plane was set such that the geometric sensitivity and penetration path length in the conventional equation can be applied with respect to this virtual object plane. 8600 Rockville Pike The site is secure. An investigation of inconsistent projections and artefacts in multi-pinhole SPECT with axially aligned pinholes. Accessibility Some research groups are working on the elimination of the DOI effect for MPH SPECT. An official website of the United States government. GATE: a simulation toolkit for PET and SPECT. The pinhole acceptance angle is 32.5 and peripheral pods are tilted towards the central pod by 16.25. An Efficient Sensitivity Calculation of Tilted Apertures for Preclinical Multi-pinhole SPECT. For (C), there is ~93% usage with ~33% multiplexing and no truncation. Derivation of system matrix from simulation data for an animal SPECT with slit-slat collimator. vs. 2.97 cm1 at 364 keV (39). Proposed small organ MPH collimator [courtesy of Bae et al. However, obtaining an experimental and Monte Carlo based system response matrix is time consuming even when interpolations and variance reduction methods (74,75), e.g., force detection techniques, are applied. A collimator is made of high-atomic number and high-density materials such as tungsten and lead which highly absorb incident photons except those traveling through holes of known angulation. Clinical utility of dopamine transporter single photon emission CT (DaT-SPECT) with (123I) ioflupane in diagnosis of parkinsonian syndromes. Van Audenhaege et al. (B) After the scan volume selection, the collimator plates and gamma detectors move into scanning position (arrows). National Library of Medicine The performance of W and DU-238 was found to be similar, while pinholes with 23 mm aperture sizes had the best results in terms of signal-to-noise ratio (SNR). Evaluation of early-stage Parkinsons disease with 99mTc-TRODAT-1 imaging. Lead and tungsten pinhole inserts for I-131 SPECT tumor imaging: experimental measurements and photon transport simulations. Bal et al. Quantification of the multiplexing effects in multi-pinhole small animal SPECT: a simulation study. Bowsher J, Yan S, Roper J, Giles W, Yin FF. At the focal point of the apertures the spatial resolution and sensitivity of the system are 4.8 mm and 973.0 cps/MBq, respectively. GEANT4 application for tomographic emission (GATE) (90) simulations for the four scanners were performed to evaluate the systems in terms of sensitivity and spatial resolution by using a point source placed at the CFOV. Academic Press, 2004. A full-ring multi-lofthole collimator, which consists of a tungsten ring with loftholes, is mounted on the system with a shutter mechanism that controls the projection overlapping and also provides complete angular sampling without the need for rotational acquisition. The adverse effect of multiplexing can also be corrected during iterative image reconstruction (62). SPECT/CT in tumor imaging: technical aspects and clinical applications. [5]. (8) designed a 14-pinhole cardiac collimator based on a target resolution of 1 cm, FOV of 20 cm and H-mode rotational acquisition for a clinical SPECT scanner by maximizing the sensitivity. The smallest diameter collimator contains 54 pinholes with a bore diameter of 398 mm. They found that at least five pinholes are required to adequately reconstruct the point sources, and FWHMs of the MPH collimators are smaller than that of the parallel-hole collimator, i.e., ~911 mm (depending on the number of the pinholes) versus 12 mm. Another aperture design that uses square- or rectangular-pinholes with a square or rectangular FOV was proposed by Metzler et al.
Bocher M, Blevis IM, Tsukerman L, Shrem Y, Kovalski G, Volokh L. A fast cardiac gamma camera with dynamic SPECT capabilities: design, system validation and future potential. Effect of overlapping projections on reconstruction image quality in multipinhole SPECT. These two iterative steps are repeated until the multiplexing artifacts are considered to be eliminated or adequately reduced. Hubbell JH. For imaging smaller objects than the detector (e.g., organs or tumors), the trade-off between spatial resolution and sensitivity compared to a conventional parallel-hole collimator can be improved upon with the use of converging collimators for organ-specific SPECT applications (31). Investigation of imaging properties for submillimeter rectangular pinholes. In (D), there is 100% usage with ~38% multiplexing and truncation. The pinholes were located as shown in Figure 19 and all of them were tilted towards the CFOV. The ring is formed by 9 large FOV cameras using 595 mm 472 mm NaI (Tl) scintillation crystals. Focused pinhole gamma detection device. For the brain phantom, the image quality improves as the number of the pinholes increases and at least eight pinholes are required to generate images without significant artifacts. Bhusal et al. (C) Comparison of resolution of G-SPECT-I equipped with a 38 cm collimator with a dual head Siemens Symbia system at equal scan time and equal dose based on physical experiments (with permission of MILabs B.V. Utrecht, The Netherlands). Aperture-to-detector distance was set to 12 cm. Lyon, France: IEEE Nuclear Science Symposium and Medical Imaging Conference Record, 2018. (7) proposed the placement of an MPH collimator on one head of a SPECT system and a fan-beam collimator on the other head (Figure 15). They evaluated 3 to 12 knife-edge pinholes for each camera with no multiplexing (Figure 24). (A) G-SPECT-I system with three optical cameras and a user interface for volume-of-interest (VOI) selection; (B) multi-pinhole collimator of G-SPECT-I system. Single photon emission computed tomography (SPECT) is an important imaging modality for various applications in nuclear medicine. As shown in Figure 8, a low number of pinholes in a regular arrangement combined with multiplexing may result in ghost artifacts, i.e., for 4-pinhole in this case. Technical considerations such as pinhole aperture design, effect of multiplexing, sampling and depth of interaction (DOI) are firstly presented in the next section. Beekman FJ, inventor; MILabs BV, assignee. [2]. Since then MPH collimation was investigated and applied more and more often for clinical applications.
Cardiovascular disease is the greatest cause of mortality and morbidity in the world and SPECT is one of the most established imaging methods to assess myocardial perfusion. Compared to simple analytical reconstruction methods such as filtered back-projection, statistical reconstruction methods can incorporate the random nature of photon detection and allow compensation of various image quality degradation effects in the acquisition process via accurate system matrix modelling (70). Projections of an XCAT phantom representing a female patient in supine position were simulated. Monte Carlo simulations of a digital mouse phantom with different numbers of pinholes. (B) Photograph of one of the many identical platinumiridium inserts. 52nd Annual Meeting of the Society of Nuclear Medicine, 2005.
Moore SC, Cervo M, Metzler SD, Udias JM, Herraiz JL. Klein WP, Barrett H, Pang IW, Patton DD, Rogulski MM, Sain J, Smith W. FASTSPECT: electrical and mechanical design of a high-resolution dynamic SPECT imager. Jaszczak RJ, Li J, Wang H, Zalutsky MR, Coleman RE. The results showed that the proposed system has a spatial resolution of 10.0 mm and a sensitivity of 0.081%, while they were 20.1 mm and 0.084%, 15.0 mm and 0.049%, 15.2 mm and 0.011% for the D-SPECT, GE Discovery NM 530c and conventional dual head GE Infinia, respectively. On the other hand, sensitivity, which is also spatially variant, is the ratio of the detected photons to the emitted photons and can be expressed as detected percentage or as cps/MBq (SI unit of radioactivity). Both designs have a better performance than the LEHR collimator, which has a resolution of 12 mm and sensitivity of 0.010%. Left: experimental setup of the 9-pinhole MPI SPECT system with a torso phantom. Lead shielding was used inside the collimator to prevent multiplexing of the pinhole projections. Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). During this process, determination of the incident angle of gamma-photons on the detector is crucial. Developing an accurate mathematical model of the sensitivity and resolution profile of the keel-edge collimator is challenging. This algorithm estimates both the values of all image voxels, and the de-multiplexed projection data from each of the pinholes. (87)]. In this way the incident angle of the detected gamma-rays is determined. Shown are the 2 cm thick aperture plate with a single aperture per detector and the 23 hexagonal detectors (courtesy of Dr. Kesava S. Kalluri). In their designs, the patient lies prone on a specially designed bed with the scanner underneath. [1] (43). A sample 9-pinhole collimator (MPGP) mounted on a clinical SPECT scanner. Xia D, Moore SC, Park MA, Cervo M, Metzler SD. Experimental evaluation of a multi-pinhole collimator for a small organ by using a small-field-of-view gamma camera. (10) designed and evaluated two MPH collimators for brain SPECT to image cerebral blood flow and striatum (Figure 17) based on a GE Inifinia Hawkeye scanner. FOIA Monte Carlo calculations in nuclear medicine: Applications in diagnostic imaging, second edition. They assessed the feasibility of maneuvering the SPECT collimator system around the patient in position for radiation therapy, allowing an unrestricted therapy procedure. The SNR (defined by mean/standard deviation) of MPH collimators was found to be much worse compared to that of the parallel-hole collimator, i.e., 10 versus 60. Deprez K, Pato LR, Vandenberghe S, Van Holen R. Characterization of a SPECT pinhole collimator for optimal detector usage (the lofthole). The ROR is set to 167 mm to provide a FOV of 20 cm to accommodate the patients head, without touching the patients shoulder. Korevaar MA, Heemskerk JW, Beekman FJ. Nguyen MP, Goorden MC, Kamphuis C, Beekman FJ. The pinhole diameter was defined as 3 mm, with a collimator plate thickness of 10 mm. Measurement of absolute myocardial blood flow in humans using dynamic cardiac SPECT and 99mTc-tetrofosmin: Method and validation. The knife-edge pinholes have an acceptance angle of 42 and a diameter of 2.7 mm. Shrestha U, Sciammarella M, Alhassen F, Yeghiazarians Y, Ellin J, Verdin E, Boyle A, Seo Y, Botvinick EH, Gullberg GT. Lyon, France: 2000 IEEE Nuclear Science Symposium. Busca et al. The MPH collimator provides high resolution and sensitivity for imaging the striatal region and the fan beam collimator provides lower resolution but complete sampling of the brain. Spatial resolution was found to be 1.0 cm at 12.7 cm from the pinhole plate and the system sensitivity was found to be 750 cps/MBq at 11.5 cm from the pinhole plate (76). Wang Y. (64) proposed an MPH SPECT system for MPI to increase the sensitivity by 5-fold while maintaining the same image quality compared to a conventional rotational SPECT system with a low-energy general-purpose (LEGP) parallel hole collimator. PMC legacy view For example, the heart or the brain can be imaged much more efficiently by fan beam, cone beam or focused pinhole collimators, which can result in better trade-off in spatial resolution and sensitivity (32). Phys Med Biol 2009;54:N267-72.
In: Proceedings of IEEE NSS-MIC, 2015. Molecular breast imaging using a fully tomographic stationary clinical cardiac SPECT scanner: a phantom study. In: Matsuda H, Asada T, Tokumaru A. The preliminary prototype design of AdaptiSPECT-C together with a cropped XCAT phantom positioned inside. The first one is a two-sphere phantom comprised of two spherical sources with a diameter of 5 mm, one located at the CFOV and the other located 20 mm offset from the CFOV. (85). The diameter of each rod is 5 mm. The system is based on simultaneous acquisitions of multiple projections from multiple detectors where each one is coupled with an individual pinhole (Figure 22). Several strategies have been attempted to further improve the detection efficiency in MPH SPECT (30). Furthermore, Korevaar et al. Effects of pinhole material and aperture size on lesion contrast and SNR breast SPECT. Accomplishing this for SPECT/MRI is still being researched for clinical brain imaging (98-100).