Introduction: Image quality and accuracy of in vivo activity quantification in SPECT are affected by Collimator penetration and scatter components, especially in high energy imaging. These phenomena highly depend on the Collimator characteristic and photon energy. The presence of penetrated and scattered photons from Collimator in SPECT images degrades spatial resolution, contrast and image quality. Knowledge of penetration and scatter distribution is essential for optimization of Collimator design and development of reconstruction algorithms. The aim of this study to survey the Collimator performance of the newly developed HiReSPECT dual head gamma camera with pixelated array CsI (Na).Methods: We modeled the HiReSPECT, by using SIMIND Monte Carlo simulation code. The contribution of geometric, scatter and penetration components were quantitatively calculated for the different energy sources. Then we compared these results with simulation results of another small animal SPECT with compact pixelated array CsI (Tl) detector.Results: The simulated System spatial resolution and energy resolution of the HiReSPECT at 140keV respectively are 1.9mm and 29.72 keV (21.23%) FWHM at 2.5cm distance from detector surface also Geometric, penetration, and scatter at 140keV for the HiReSPECT Collimator are 96.42%, 2.22%, 1.30%, respectively. Similarly, geometric, penetration, and scatter at 159keV and 245keV for this system Collimator are (95.24%, 3.08%, 1.68%) and (87.21%, 8.10%, 4.69%), respectively.Conclusion: The results verified that the magnitude of these components depend on Collimator geometric structure and photons energy. The measured performances indicated that the HiReSPECT scanner is well suited for preclinical molecular imaging research and provide high resolution for small animal imaging.

Objective(s): The purpose of this study was to examine the optimal reconstruction parameters for brain dopamine transporter SPECT images obtained with a fan beam Collimator and compare the results with those obtained by using Parallel-Hole Collimators.Methods: Data acquisition was performed using two SPECT/CT devices, namely a Symbia T6 and an Infinia Hawkeye 4 (device A and B) equipped with fan-beam (camera A-1 and B-1), low- and medium-energy general-purpose (camera A-2 and B-2), and low-energy high-resolution (camera A-3 and B-3) Collimators. The SPECT images were reconstructed using filtered back projection (FBP) with Chang’s attenuation correction. However, the scatter correction was not performed. A pool phantom and a three-dimensional (3D) brain phantom were filled with 123I solution to examine the reconstruction parameters. The optimal attenuation coefficient was based on the visual assessment of the profile curve, coefficient of variation (CV) [%], and summed difference from the reference activity of the pool phantom. The optimal Butterworth filter for the 3D-brain phantom was also determined based on a visual assessment. The anthropomorphic striatal phantom was filled with 123I solution at striatum-to-background radioactivity ratios of 8, 6, 4, and 3. The specific binding ratio (SBR) of the striatum (calculated by the CT method) was used to compare the results with those of the Parallel-Hole Collimators.Results: The optimal attenuation coefficients were 0.09, 0.11, 0.05, 0.05, 0.11, and, 0.10 cm-1 for cameras A-1, A-2, A-3, B-1, B-2, and B-3, respectively. The cutoff frequencies of the Butterworth filter were 0.32, 0.40, and 0.36 cycles/cm for camera A, and 0.46, 0.44, and 0.44 cycles/cm for camera B, respectively. The recovery rates of the SBRmean with camera A were 51.2%, 49.4%, and 45.6%, respectively. The difference was not statistically significant. The recovery rates of the SBR with camera B were 59.2%, 50.7%, and 50.8%, respectively. Camera B-1 showed significantly high SBR values. Conclusion: As the findings indicated, the optimal reconstruction parameters differed according to the devices and Collimators. The fan beam Collimator was found to provide promising results with each device.

Performance of Parallel-Hole Collimators may be evaluated by determining their response to a point radioactive source which for instance, the amount of Collimator resolution is calculated by measuring the full width at half maximum (FWHM) of point spread function (PSF). The conventional method in calculating the response of the Collimator to a point source by using Monte Carlo simulations is to map the signal values in each detector cell to the center of cell on the x or y axis. In this paper, a new computing algorithm has been proposed which optimally maps the signal values on these axes. The responses of LEUHR, LEHR, LEGP and LEHS Collimators are simulated based on the conventional method and the optimized computing one by the MCNP5 code. The results have been indicated that the response based on the optimized method has a higher accuracy compared to that of the conventional one. The average relative differences between the amounts of resolution based on the optimized method and experimental data have been found to be considerably fewer than those of the conventional one. Therefore, one may obtain Parallel Hole Collimators’ response with a higher accuracy by using the optimized computing method.

In Single Photon Emission Computed Tomography (SPECT), Collimator selection, optimization, and also geometric calibration have a major impact on the acquired image quality and also on an accurate detectability and diagnosis. The Collimator optimization phenomena consider some parameters such as field of view, resolution, sensitivity, resolution at depth, septal thickness and penetration for a specific application task. While the Parallel Hole Collimator is usually used in SPECT and planar imaging but due to the limited solid angle covered by the Collimator, the system sensitivity and resolution were highly reduced. Meanwhile, other types of Collimators such as pin-Hole, multi-pin-Hole, slant and slit-slat Collimators were introduced with a trade-off between sensitivity and resolution. This article reviews improvements on Collimators also by considering the geometry and geometric calibration methods for improving the image quality in single photon emission computed tomography.

Introduction: The Adaptive Quality Control Phantom (AQCP) is the computer-controlled phantom which positions and moves a radioactive source in the Field of View (FOV) of an imaging nuclear medicine device on a definite path to produce any spatial distribution of gamma rays to perform the QC Tests such as the Collimator Hole Angulation (CHA) and the Center OF Rotation (COR) of Single Photon Emission Computer Tomography (SPECT).Methods: The Collimator Hole angulation for three Collimators were measured with the method by using a point source and computer-controlled cylindrical positioning. In this method the displacement of the image of a point source examined as the AQCP move point source vertically away from the Collimator face. A new method for center of rotation assessment by AQCP is introduced and the results of this proposed method as compared with the routine QC test (IAEA-TECDOC-602 method) and their differences are discussed in detail.Results: The results of the high-accuracy measurement method of CHA show that the measurement accuracy for absolute angulation errors is better than ±0.024°. The Root Mean Square (RMS) of CHA for LEHR, LEHS and LEUHR Collimators were measured to be 0.290°, 0.292° and 0.208° respectively. In addition, it has been proved and established that the precise measurement of the distance of the point source movement vertically away from the Collimator face has had a great effect on the CHA measurement. It is to be added in this connection that the measured RMS of CHA for LEHR Collimator with the distance variation from the Collimator's surface+/-1 mm has been varied+/-0.04 degree.Conclusion: Based on such comparison between the two afore-described methods, it proofs the mechanical problems of detector rotation should be considered as the main cause of the difference between the two methods under consideration. We defined and measured a new parameter called Dynamic Mechanical Error (DME) for applying the gantry motion correction.

While the conventional Parallel-Hole Collimators are widely used in myocardial perfusion imaging (MPI) with SPECT, they are suboptimal in balancing the existing sensitivity-resolution compromise. Therefore, multi-pinHole collimation has been proposed to address the problem. In the present study, a channel multi-pinHole collimated SPECT scanner is modeled and then simulated using the GATE Monte Carlo simulation. The multi-pinHole Collimator comprises eight apertures. The material, diameter, and height of the apertures were assumed to be varying. A comparison with conventional single-pinHole was also conducted. The results show that increasing the Hole diameter leads to degraded spatial resolution for the multi-pinHole Collimator. Compared to the single-pinHole, the multi-pinHole Collimators suffer from projection overlapping and thus deteriorated spatial resolution. The findings confirm that the channel multi-pinHole Collimators outperform the single-pinHole apertures by providing much higher sensitivity at the expense of slightly lower spatial resolution and therefore would be the Collimator of choice for MPI with SPECT.

Introduction: Converging Collimator has special application in nuclear medicine. Converging Collimator are used primarily with cameras having large-area detectors to permit full utilization of the available detector area for imaging of small organs such as thyroid. Because of inherent magnification of converging Collimator, it can provide higher image quality of small objects. Accurate spatial resolution and efficiency Measurement of this Collimator, therefore, can have significant role in design and development of these Collimators. The aim of this research is accurate modeling of converging Collimator for surveying of spatial resolution and efficiency as a function of axial distance from Collimator face by Monte Carlo code.Methods: A simplified model of converging Collimator based on an actual model was simulated by MCNP Monte Carlo code. The spatial resolution was measured in 2cm, 5cm, 8cm and 10 cm from Collimator face. The efficiency was also measured in 1cm, 2cm, 3cm, 4cm and 5cm from Collimator face.Results: From the results, the spatial resolution of the system (MTF=0.1) increased from 2.15 cycle/cm at axial distance of 2 cm to 1.05 cycle/cm at axial distance of 10 cm. (1.75 and 1.4 cycle/cm at axial distances 5 and 8 cm, respectively). The efficiency of the system at mentioned axial distances increased from 8.9 E-5 to 7.97 E-4. In addition, the results of this simulation have acceptable accordance with prior analytic results in this field that can validate simulated system.Conclusion: From results of simulation one can deduce that spatial resolution of this Collimator will decrease with increase in axial distance from Collimator face. Because of magnification effect, rate of spatial resolution reduction in axial distance is lesser than Parallel Hole Collimator. Thus, this feature of converging Collimator provides better image quality in nuclear images at expense of decreased field size. The efficiency of these Collimators has a direct proportion with axial distance from Collimator face and improved with increasing distance. Thus, a design of a Collimator that provides both high spatial resolution and acceptable efficiency has noticeable importance.

Introduction: In an ideal Parallel-Hole Collimator, thickness of septal material should be sufficient to stop more than 95% of incident photons. However, some photons pass the septa without interaction or experience scattering before they reach the detector. In this study, we determined different contribution of Collimator responses consist of geometrical response, septal penetration (SP) and scattering (SC) for low, medium and high energy Collimators.Methods: A point source of activity with common energies in diagnostic nuclear medicine and three different Collimators were simulated using SIMIND Monte Carlo code.Results: For Low Energy High Resolution (LEHR) Collimator, SP was increased from 7% in 140 keV to 30% in 167keV and more than 75% in energies higher than 296keV. SC also was increased from 4% in 98keV to more than 15% in energies higher than 167keV and reached to its maximum (26%) in 296keV. For Medium Energy All Purpose (MEAP) Collimator, SP was suddenly increased from 6% in 186keV to 28% for 296keV and more than 50% for higher energies. SC was also increased from 4% in energies below 186keV to 15% in 296keV and about 30% for higher energies. For High Energy (HE) Collimator, SP was about 20% for 364keV photons. SC was 15% for 364keV photons and only 65% of photons were geometrically collimated.Conclusion: Our results showed that even by using nominally suitable Collimators, there are considerable SC and SP that influence the quantitative accuracy of planar and SPECT images. The magnitude of geometrical response, SC and SP depend on Collimator geometric structure and photons energy.