This stationary system has the potential to be integrated with an MRI system. Photons being detected with a larger incident angle would be more blurred out (red point spread function) compared to those with a smaller incident angle (blue point spread function). 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.
For MPH SPECT reconstruction, the system response matrix can be calculated based on Monte Carlo simulation or analytical techniques, and can be combined with an experimental characterization (71-73). Photon cross sections, attenuation coefficients, and energy absorption coefficients from 10 keV to 100 GeV 1969 National Bureau of Standards (U.S.) Rep. NSRDS-NBS 29. During this process, determination of the incident angle of gamma-photons on the detector is crucial. Temporal shuttering of apertures to enhance axial and angular sampling in a multi-pinhole SPECT system for brain imaging. The thickness of the pinhole plate is 1 cm and each pinhole has a knife edge at the half depth of the pinhole plate. A comparison of FDG-PET and blood flow SPECT in the diagnosis of neurodegenerative dementias: A systematic review. Angular sampling of the base configuration was enhanced by adding the temporal shuttering of two additional apertures per detector positioned laterally to either side of the central aperture. King et al. In: Proceedings of IEEE NSS-MIC, 2015. Hwang AB, Iwata K, Hasegawa BH, editors. To facilitate early diagnosis for potential treatment, the development of high-resolution brain SPECT is in demand. Distortions manifest outside this region, especially towards the edge of the object in the axial direction (Figure 7). Single photon emission computed tomography (SPECT) is an important imaging modality for various applications in nuclear medicine. Proposed small organ MPH collimator [courtesy of Bae et al. Two groups of five detectors are tilted and positioned on each side of the nine detectors in the main row. Bhusal N, Dey J, Xu J, Kalluri K, Konik A, Mukherjee JM, Pretorius PH. Right: sample pinhole aperture from Discovery NM 530c (courtesy of Taipei General Veterans Hospital). This effect causes blurring in the final reconstructed image and is called the DOI or parallax effect. The multiplexing effect can be reduced by several strategies, including baffle (61), the aforementioned dual stage collimation, loftholes, and rectangular pinholes. Monte Carlo simulations of a digital mouse phantom with different numbers of pinholes. The detected gamma rays are transformed into electronic signals to form 2D projection images from which the 3D map of the radiotracer distribution in the body is reconstructed. 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. (97). designed and evaluated an organ specific small FOV MPH collimator (84). The ring is formed by 9 large FOV cameras using 595 mm 472 mm NaI (Tl) scintillation crystals. FJB reports personal fees and non-financial support from MILabs, grants from Dutch Foundation for Scientific Research (NWO), during the conduct of the study. [5]. Careers. Wang B, van Roosmalen J, Kreuger R, Huizenga J, Beekman FJ, Goorden MC. Besides the increased sensitivity from a greater number of pinholes when the pinholes are focused to cover a common volume, MPH collimators can obtain multiple projections at a single detector position, which can improve the angular and axial sampling compared to the single pinhole collimator (34-36). (80) designed and simulated a full-ring multi-lofthole brain SPECT based on the modification of an existing PET detector ring made of 24 LaBr3 sub-detectors (LaPET, Figure 13). The proposed design consists of two detector rings with 35 cm in diameter and is inserted into a 3T MRI system with 59 cm bore size. The hole diameter is 3 mm and the aperture-to-detector distance is set to 70 mm. Smith et al. Lyon, France: IEEE Nuclear Science Symposium, Medical Imaging Conference Record, 2016. pinhole (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). The system is based on simultaneous acquisitions of multiple projections from multiple detectors where each one is coupled with an individual pinhole (Figure 22). Measurement of absolute myocardial blood flow in humans using dynamic cardiac SPECT and 99mTc-tetrofosmin: Method and validation. 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. Hubbell JH. for detecting breast tumors (11) that was then further developed and characterized by Wang et al. Highlights lecture EANM 2015: the search for nuclear medicines superheroes. 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). PMC legacy view A pinhole gamma camera with optical depth-of-interaction elimination. Semi-stationary acquisition mode with 1-step detector rotation for both detectors showed reduced artifacts compared to the fully stationary acquisition. (A) Transparent plates compress the breast and a VOI is selected using optical cameras. Vaissier PE, Goorden MC, Vastenhouw B, van der Have F, Ramakers RM, Beekman FJ. 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. Before Conversely, collimators with smaller holes provide better spatial resolution with lower sensitivity. 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. Simulation study on a stationary data acquisition SPECT system with multi-pinhole collimators attached to a triple-head gamma camera system. The system design parameters are: 19.3 cm radius of rotation (ROR), 0.75 cm aperture diameter, 31.5 cm system radius, 65.4 acceptance angle and 21 cm FOV. DiFilippo et al. Pinhole-to-ROI distance ranges from 15 to 22 cm as the detector moves around the patient. (B) After the scan volume selection, the collimator plates and gamma detectors move into scanning position (arrows). Monte Carlo calculations in nuclear medicine: Applications in diagnostic imaging, second edition. Dashed lines inside the detector and the pinhole plate show their central plane, respectively. Van Patten R, Greif T, Britton K, Tremont G. Single-photon emission computed tomography (SPECT) perfusion and neuropsychological performance in mild cognitive impairment. demonstrated that for 123I DaTscan imaging, total scatter, multiple scatters, and penetration events for the low energy high resolution (LEHR) parallel-hole collimators were 2.5, 7.6 and 14 times more than that of an MPH collimator within the 15% photopeak window and with a 2-cm thick tungsten aperture plate (37). Left: (A) pod geometry. 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. Various dedicated clinical cardiac, brain, thyroid, and breast MPH SPECT systems are then presented in the following sections. Lyon, France: IEEE Nuclear Science Symposium Conference Record, 2001. Design and simulation of a high-resolution stationary SPECT system for small animals. Developing an accurate mathematical model of the sensitivity and resolution profile of the keel-edge collimator is challenging. Tornai et al. [. in 1993 (77) and developed by Klein et al. The proposed method addresses data sufficiency and a larger volume-of-interest can be covered which includes the occipital lobe for the calculation of striatal binding ratio. 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). European Patent Application EP2073039. The yellow star represents the origin of the gamma ray. Binding of [99mTc]TRODAT-1 to dopamine transporters in patients with Parkinsons disease and in healthy volunteers. Each pinhole is coupled to a 7.6 cm wide circular detector with an active area of 7 cm in diameter. U-SPECT systems (50,51) employ dual stage collimation to effectively achieve non-multiplexing, i.e., non-overlapping projections (Figure 4). Right: non-multiplexed projection data of the phantom with cardiac and liver uptakes [courtesy of Funk et al. The use of multi-pinhole (MPH) collimators can provide superior resolution-sensitivity trade-off when imaging small field-of-view compared to conventional parallel-hole and fan-beam collimators. [12] (57). The gamma camera used in the simulation employs a NaI(Tl) scintillation crystal with 3.5 mm intrinsic spatial resolution. Proposed design of the integrated SPECT/MRI instrument (courtesy of Busca et al. For the cases where many bed positions are needed, the acquisition time could be reduced dramatically by helical trajectories. 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). Nguyen MP, Goorden MC, Kamphuis C, Beekman FJ. It has a C-shaped gantry, which accommodates multiple cadmium zinc telluride (CZT) detectors (Figure 12). (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). The system is being constructed at the University of Arizona. Huang WS, Lin SZ, Lin JC, Wey SP, Ting G, Liu RS. The smallest rod that can be resolved of a Derenzo resolution phantom with rod dimeter equals to rod distance is 2.5 mm and 3.5 mm, with a peak sensitivity of 415 cps/MBq and 896 cps/MBq (compared to 182 cps/MBq for a conventional dual-head camera) for the ultrahigh resolution (UHR) collimator and high resolution (HR) collimator respectively. sconces The pixel size of the CZT detectors is 2.46 mm. Projections from the pinhole collimator may suffer more from the DOI effect compared to other collimators when the incident angles are large. A sample 9-pinhole collimator (MPGP) mounted on a clinical SPECT scanner. 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. Xia D, Moore SC, Park MA, Cervo M, Metzler SD. Left ventricle counts were used to evaluate the system sensitivity and then compared to a state-of-the-art scanner (89). This algorithm estimates both the values of all image voxels, and the de-multiplexed projection data from each of the pinholes. A novel approach to multipinhole SPECT for myocardial perfusion imaging. A user interface that employs three optical cameras is used to select the scan region to maximize the focus capabilities (83). In (D), there is 100% usage with ~38% multiplexing and truncation. Quantification of the multiplexing effects in multi-pinhole small animal SPECT: a simulation study. Note that for G-SPECT, FASTSPECT and many other MPH SPECT systems, fast SPECT (sub-second) acquisitions are inherently feasible. In: Matsuda H, Asada T, Tokumaru A. (33) used seven pinholes to obtain simultaneous projections of an emission source onto seven independent regions of an Anger scintillation camera. The system spatial resolution for the MPH was set to 4.7 mm at the focal point of the apertures, which is comparable to that of a clinical PET system. Furenlid LR, Wilson DW, Chen YC, Kim H, Pietraski PJ, Crawford MJ, Barrett HH. Momsen NC, Richards G, King MA, Zeraatkar N, Furenlid LR. Rowe RK, Aarsvold JN, Barrett HH, Chen JC, Klein WP, Moore BA, Pang IW, Patton DD, White TA. Dashed lines indicate the pinhole axes, which converge on a line 40 mm from the collimator. showed that the axial spatial resolution and sensitivity of single pinhole SPECT system can be improved by using three-pinhole collimators (34). Furthermore, Korevaar et al. Funk et al. The system consists of 7 pods, i.e., one central pod and six peripheral pods, and each pod has a cluster of seven pinholes which target the same FOV. Left: LaPET scanner with a collimator insert. In the standard general-purpose mode (MPGP), the collimator is used for cerebral blood flow imaging, while in the high-resolution mode (MPHR), the collimator is used for DaT imaging. This trade-off needs to be considered for different applications and gamma-ray energy to determine the optimal collimator design for a certain application. Tomas MB, Pugliese PV, Tronco GG, Love C, Palestro CJ, Nichols KJ. The normalized mean square error (NMSE) was calculated for the reconstructed images versus the original source distribution. Since then MPH collimation was investigated and applied more and more often for clinical applications. Van Audenhaege K, Van Holen R, Vanhove C, Vandenberghe S. Collimator design for a multipinhole brain SPECT insert for MRI. van der Have F, Vastenhouw B, Ramaker RM, Branderhorst W, Krah JO, Ji C, Staelens SG, Beekman FJ. They found that increasing the channel height resulted in a higher spatial resolution but also a rapid decrease in sensitivity for off-axis sources. Shrestha U, Sciammarella M, Alhassen F, Yeghiazarians Y, Ellin J, Verdin E, Boyle A, Seo Y, Botvinick EH, Gullberg GT. The main advantage of the rectangular FOV compared to a circular FOV is that the projections can be packed more efficiently. Anaheim, CA, USA: 2012 IEEE NSS-MIC (M21-43), 2012. The system sensitivity was found to be 6.1 times higher than that of a single pinhole collimator. 1Biomedical Imaging Laboratory, Department of Electrical and Computer Engineering, Faculty of Science and Technology, University of Macau, Macau, China; 2Department of Biomedical Engineering, Faculty of Engineering, Near East University, Nicosia/TRNC, Mersin-10, Turkey; 3DESAM Institute, Near East University, Nicosia/TRNC, Mersin-10, Turkey; 4Department of Imaging, Dana Farber Cancer Institute, Boston, MA, USA; 5Department of Radiology, University of Massachusetts Medical School, Worcester, MA, USA; 6Section of Biomedical Imaging, Department of Radiation Science and Technology, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands; 7MILabs B.V, Heidelberglaan 100, 3584 CX, Utrecht, The Netherlands; 8Department of Translational Neuroscience, Brain Center Rudolf Magnus, University Medical Center Utrecht, The Netherlands; 9Center for Cognitive and Brain Sciences, Institute of Collaborative Innovation, University of Macau, Macau, China. (55)]. Slomka PJ, Patton JA, Berman DS, Germano G. Advances in technical aspects of myocardial perfusion SPECT imaging. Mahmood ST, Erlandsson K, Cullum I, Hutton BF. (95)]. Characterization of a multi-pinhole molecular breast tomosynthesis scanner. The DOI effect can be negligible for gamma rays interacting with the detector at a right angle. Besides the very successful application in small animal imaging, there has been a resurgence of the use of MPH collimators for clinical cardiac and brain studies, as well as other small field-of-view applications. (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. Mok GSP, Tsui BMW, Wang Y, Du Y, Segars WP, Frey EC. government site. They also calculated the pinhole acceptance angle to keep the number of pinholes constant, and optimized sensitivity at several target system resolutions. The aperture size of this 12-pinhole design (Figure 18) is 4.65 mm, while the imaging distance is 18.6 cm and aperture-to-detector distance is 15.8 cm. Lyon, France: IEEE NSS/MIC Conf. Conference Record (Cat. Another advantage of MPH collimators is the large reduction in collimator penetration versus parallel-, cone- or fan-beam collimators. Projections of an XCAT phantom representing a female patient in supine position were simulated. Wang Y. The new PMC design is here! Si et al. The detector configuration is based on the original design proposed by Dey (96) and further improved by Kalluri et al. The choice of aperture depends on the photon energy for the specific application. MPH collimators are tilted to cover the FOV. (63) developed spiral trajectories of the animal bed to improve temporal resolution and reduce image reconstruction time. 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). (85)]. (85). In addition, GSPM serves as an unpaid editorial board member of Quantitative Imaging in Medicine and Surgery. 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). Mok et al. where d is the physical hole diameter, is the incident angle, l is the imaging distance, is the attenuation coefficient of the aperture material, and is the acceptance angle of the pinhole (Figure 2). This stationary system has the potential to be integrated with an MRI system. Photons being detected with a larger incident angle would be more blurred out (red point spread function) compared to those with a smaller incident angle (blue point spread function). 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.
This stationary system has the potential to be integrated with an MRI system. Photons being detected with a larger incident angle would be more blurred out (red point spread function) compared to those with a smaller incident angle (blue point spread function). 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.