High-resolution Parallel-hole Collimator Research Articles

Reduction in variability of dopamine transporter measures using SPECT and ultra-high-resolution fan beam collimators: comparison with parallel-hole collimators in healthy controls for a clinical reference database

PurposeThe purpose of this study was to create 123I-FP-CIT reference values for ultra-high-resolution fan beam collimators (UHR-FB) from a sample of subjects without dopaminergic degeneration and to compare them to a normal database -PPMI database- of a commercial software (DaTQUANT) obtained using high-resolution parallel-hole collimators (HR-PH).MethodsA striatal phantom study was performed to compare UHR-FB with HR-PH and to obtain a correction factor between collimators. Normal 123I-FP-CIT studies from 177 subjects acquired using UHR-FB were retrospectively selected on the basis of visual and semi-quantitative analysis as well as of the neurological follow-up (range of 2–9 years). SPECT images were reconstructed using the same parameters of DaTQUANT normal database and SBR values were obtained for striatal structures. Correction factor was applied to the UHR-FB database to test differences against DaTQUANT database.ResultsCorrection factor obtained from the phantom study was 0.84. Uncorrected SBR values of the local database were significantly higher than PPMI database values, but no significant differences were found using corrected values. Coefficients of variations of SBR values were significantly lower in a local database than PPMI database (15% vs 20%). Significant effects of age on SBR were observed in both databases with a reduction rate for a decade of 6% in the PPMI database and 4.5% in the local database. In the latter, women had slightly higher SBR values and a steeper decline with advancing age compared to men, whereas no significant gender differences were found in the PPMI database.ConclusionThe SBR values obtained using UHR-FB have an age-related distribution comparable to that of healthy subjects but with lower variability. The reduction rate per decade was similar between the two databases but the gender effect was found only in the local database, probably related to the better performance of UHR-FB.

Evaluation of Interstitium by Lymphatic Uptake Method in Chronic Bilateral Lower Extremity Edema.

Symmetrical bilateral lower extremity edema (BLEE) needs to be treated effectively. Finding the cause of this condition increases the success of treatment. Fluid increase in the interstitial space (FIIS) is always present as a cause or a result. Subcutaneously administered nanocolloid is transported by uptake by lymphatic pre-collectors, and this uptake takes place in the interstitium. We aimed to evaluate the interstitium with labeled nanocolloid and contribute to the differential diagnosis in cases with BLEE. Our retrospective study included 74 female patients who underwent lymphoscintigraphy for bilateral lower extremity edema. Technetium 99m (Tc-99m) albumin colloid (nanocolloid), a marked colloidal suspension, was applied subcutaneously to two different areas on the dorsum of both feet with a 26 gauge needle The dose volume administered intradermally is approximately 0.2-0.3 ml, and each injector has 22-25MBq of activity. Siemens E-Cam dual-headed SPECT gamma camera was used for imaging. Dynamic and scanning images were taken with a high-resolution parallel hole collimator. Ankle images were re-evaluated by two nuclear medicine specialists, independent of physical examination and scintigraphy findings. 74 female patients with bilateral lower extremity edema were divided into two groups based on physical examination and lymphoscintigraphy findings. There were 40 and 34 patients in Groups I and II, respectively. In the physical examination, patients in Group I were evaluated as lymphedema, and patients in Group II were evaluated as lipedema. The main lymphatic channel (MLC) was not observed in any of the patients in Group I in the early images, and the MLC was observed at a low level in the late imaging in 12 patients. The sensitivity of the presence of distal collateral flows (DCF) in the presence of significant MLC in early imaging in demonstrating increased fluid in the interstitial space (FIIS) was calculated as 80%, specificity as 80%, PPV 80%, and NPV 84%. While MLC is present in early images, concomitant DCF occurs in cases of lipoedema. The transport of increased lymph fluid production in this group of patients can be covered by the existing MLC. Although MLC is evident, the presence of significant DCF supports the presence of lipedema. It can be used as an important parameter in the diagnosis in early cases where physical examination findings are not evident.

Evaluation of different CT maps for attenuation correction and segmentation in static 99m Tc-MAA SPECT/CT for 90 Y radioembolization treatment planning: A simulation study.

Conventional 99m Tc-macroaggregated albumin (99m Tc-MAA) planar scintigraphy overestimates lung shunt fraction (LSF) compared to SPECT/CT. However, the respiratory motion artifact due to the temporal mismatch between static SPECT and helical CT (HCT) may compromise the SPECT quantitation accuracy by incorrect attenuation correction (AC) and volume-of-interest (VOI) segmentation. This study aims to evaluate AC and VOI segmentation effects systematically and to propose a CT map for LSF and tumor-to-normal liver ratio (TNR) estimation in static 99m Tc-MAA SPECT/CT. The 4D XCAT phantom was used to simulate a phantom population of 120 phantoms, modeling 10 different anatomical variations, nine TNRs (2-13.2), nine tumor sizes (2-6.7cm diameter), eight tumor locations, three axial motion amplitudes of 1, 1.5, and 2 (cm), and four LSFs of 5%, 10%, 15%, and 20%. An analytical projector for low-energy high-resolution parallel-hole collimator was used to simulate 60 noisy projections over 360°, modeling attenuation and geometric collimator-detector response (GCDR). AC and VOI mismatch effects were investigated independently and together, using cine average CT (CACT), HCT at end-inspiration (HCT-IN), mid-respiration (HCT-MID), and end-expiration (HCT-EX) respectively as attenuation and segmentation maps. SPECT images without motion, AC, and VOI errors were also generated as reference. LSF and TNR errors were measured as compared to the ground truth. HCT-MID has slightly better performance for AC effect compared with other CT maps in LSF and TNR estimation, while HCT-EX and HCT-MID perform better for VOI effect. For a respiratory motion amplitude of 1.5cm and a LSF of 5%, the LSF errors are 19.56±4.58%, -6.79±1.74%, 77.29±14.74%, and 111.25±18.29% corresponding to HCT-MID, HCT-EX, HCT-IN, and CACT in static SPECT. The TNR errors are -12.38±6.42%, -20.55±11.25%, -20.89±9.98%, and -22.89±14.38% respectively. HCT-MID has the best performance for LSF estimation for LSF>10% and TNR estimation, followed by HCT-EX, HCT-IN, and CACT. The HCT-MID is recommended for AC and segmentation to alleviate respiratory artifacts and improve quantitation accuracy in 90 Y radioembolization treatment planning. HCT-EX would also be a recommended choice if HCT-MID is not available.

A Numerical Study of Different Types of Collimators for a High-Resolution Preclinical CdTe Pixelated Semiconductor SPECT System

In single-photon-emission computed tomography (SPECT) with a pixelated semiconductor detector (PSD), not only pinhole collimators but also parallel-hole collimators are often used in preclinical nuclear-medicine imaging systems. The purpose of this study was to evaluate and compare pinhole and parallel-hole collimators in a PSD. For that purpose, we paired a PID 350 (Ajat Oy Ltd., Finland) CdTe PSD with each of the four collimators most frequently used in preclinical nuclear medicine: (1) a pinhole collimator, and (2) low-energy high-resolution (LEHR), (3) low-energy general-purpose (LEGP), and (4) low-energy high-sensitivity (LEHS) parallel-hole collimators. The sensitivity and spatial resolution of each collimator was evaluated using a point source and a hot-rod phantom. The highest sensitivity was achieved using LEHS, followed by LEGP, LEHR, and pinhole. Also, at a source-to-collimator distance of 2 cm, the spatial resolution was 1.63, 2.05, 2.79, and 3.45 mm using pinhole, LEHR, LEGP, and LEHS, respectively. The reconstructed hot-rod phantom images showed that the pinhole collimator and the LEHR parallel-hole collimator give a fine spatial resolution for preclinical SPECT with PSD. In conclusion, we successfully compared different types of collimators for a preclinical pixelated semiconductor SPECT system.

Multipinhole collimator with 20 apertures for a brain SPECT application.

Several new technologies for single photon emission computed tomography (SPECT) instrumentation with parallel-hole collimation have been proposed to improve detector sensitivity and signal collection efficiency. Benefits from improved signal efficiency include shorter acquisition times and lower dose requirements. In this paper, the authors show a possibility of over an order of magnitude enhancement in photon detection efficiency (from 7.6 × 10(-5) to 1.6 × 10(-3)) for dopamine transporter (DaT) imaging of the striatum over the conventional SPECT parallel-hole collimators by use of custom-designed 20 multipinhole (20-MPH) collimators with apertures of 0.75 cm diameter. Quantifying specific binding ratio (SBR) of (123)I-ioflupane or (123)I-iometopane's signal at the striatal region is a common brain imaging method to confirm the diagnosis of the Parkinson's disease. The authors performed imaging of a striatal phantom filled with aqueous solution of I-123 and compared camera recovery ratios of SBR acquired between low-energy high-resolution (LEHR) parallel-hole collimators and 20-MPH collimators. With only two-thirds of total acquisition time (20 min against 30 min), a comparable camera recovery ratio of SBR was achieved using 20-MPH collimators in comparison to that from the LEHR collimator study. Their systematic analyses showed that the 20-MPH collimator could be a promising alternative for the DaT SPECT imaging for brain over the traditional LEHR collimator, which could give both shorter scan time and improved diagnostic accuracy.

The effect of high-resolution parallel-hole collimator materials with a pixelated semiconductor SPECT system at equivalent sensitivities: Monte Carlo simulation studies

In nuclear medicine, the use of a pixelated semiconductor detector with cadmium telluride (CdTe) or cadmium zinc telluride (CdZnTe) is of growing interest for new devices. Especially, the spatial resolution can be improved by using a pixelated parallel-hole collimator with equal holes and pixel sizes based on the above-mentioned detector. High-absorption and high-stopping-power pixelated parallel-hole collimator materials are often chosen because of their good spatial resolution. Capturing more gamma rays, however, may result in decreased sensitivity with the same collimator geometric designs. Therefore, a trade-off between spatial resolution and sensitivity is very important in nuclear medicine imaging. The purpose of this study was to compare spatial resolutions using a pixelated semiconductor single photon emission computed tomography (SPECT) system with lead, tungsten, gold, and depleted uranium pixelated parallel-hole collimators at equal sensitivity. We performed a simulation study of the PID 350 (Ajat Oy Ltd., Finland) CdTe pixelated semiconductor detector (pixel size: 0.35 × 0.35 mm2) by using a Geant4 Application for Tomographic Emission (GATE) simulation. Spatial resolutions were measured with different collimator materials at equivalent sensitivities. Additionally, hot-rod phantom images were acquired for each source-to-collimator distance by using a GATE simulation. At equivalent sensitivities, measured averages of the full width at half maximum (FWHM) using lead, tungsten, and gold were 4.32, 2.93, and 2.23% higher than that of depleted uranium, respectively. Furthermore, for the full width at tenth maximum (FWTM), measured averages when using lead, tungsten, and gold were 6.29, 4.10, and 2.65% higher than that of depleted uranium, respectively. Although, the spatial resolution showed little differences among the different pixelated parallel-hole collimator materials, lower absorption and stopping power materials such as lead and tungsten had relatively better characteristics at specific sensitivities.

Design and development of a high resolution animal SPECT scanner dedicated for rat and mouse imaging

A dedicated small-animal SPECT system, HiReSPECT, was designed and developed to provide a high resolution molecular imaging modality in response to growing research demands. HiReSPECT is a dual-head system mounted on a rotating gantry. The detection system is based on pixelated CsI(Na) scintillator crystals coupled to two Hamamatsu H8500 Position Sensitive Photomultiplier Tubes in each head. Also, a high resolution parallel-hole collimator is applied to every head. The dimensions of each head are 50mm×100mm, enabling sufficient transaxial and axial fields-of-view (TFOV and AFOV), respectively, for coverage of the entire mouse in single-bed position imaging. However, a 50mm TFOV is not sufficient for transaxial coverage of rats. To address this, each head can be rotated by 90 degrees in order to align the larger dimension of the heads with the short body axis, allowing tomographic data acquisition for rats. An innovative non-linear recursive filter was used for signal processing/detection. Resolution recovery was also embedded in the modified Maximum-Likelihood Expectation Maximization (MLEM) image reconstruction code to compensate for Collimator-Detector Response (CDR). Moreover, an innovative interpolation algorithm was developed to speed up the reconstruction code. The planar spatial resolution at the head surface and the image spatial resolutions were 1.7mm and 1.2–1.6mm, respectively. The measurements followed by post-processing showed that the observed count rate at 20% count loss is about 42kcps. The system sensitivity at the collimator surface for heads 1 and 2 were 1.32cps/µCi and 1.25cps/µCi, respectively. The corresponding values were 1.18cps/µCi and 1.02cps/µCi at 8cm distance from the collimator surfaces. In addition, whole-body scans of mice demonstrated appropriate imaging capability of the HiReSPECT.

Clinical Utility of Radiation Medicine 99mTc-Methylene Diphosphanate Bone Scintigraphy in the Early Diagnosis of Rheumatoid Arthritis.

The value of 99mTc-Methylene diphosphanate (99mTc-MDP) bone scan in predicting development of bony destruction, swelling, new bone erosions and skeletal deformities in small joints and bones was studied by visual evaluation of bone scans. 99m Tc-MDP was injected intravenously. 3 hours after the 99mTc-MDP injection, they have been underwent spot views of entire skeletons with planar scintigraphy in the anterior and posterior positions. All patients were examined under the Electronics Corporation of India Limited (ECIL) single head gamma camera imaging machine, equipped with a low-energy high-resolution parallel-hole collimator. In 9 patients with newly diagnosed rheumatoid arthritis a total of 60 patients of 99mTc-MDP bone scan were examined clinically, scintigraphically, and radiographically. The follow up period was 2 years. Seven patients found increased radiopharmaceutical increased in small joints. Onset of the rheumatoid disease was found in three out of seven patients. 2/9 patients, the joints which were eroded scintigraphically, was active at all the checkups. Erosions were detected earlier in foot joints than in finger joints. New erosions were especially prone to appear in joints with persisting and high scintigraphic activity. On the contrary, inactive joints by radionuclide scanning never eroded. Scintigraphic and clinical activity and radiographic erosion correlated significantly with each other. The sensitivity and specificity of visual scintigraphic assessment and the relative pixel activity method proved to be superior to the region of interest methods and clinical evaluation for prediction of bony erosions in patients of rheumatoid arthritis.

Design and performance evaluation of a 20-aperture multipinhole collimator for myocardial perfusion imaging applications

Single photon emission computed tomography (SPECT) myocardial perfusion imaging remains a critical tool in the diagnosis of coronary artery disease. However, after more than three decades of use, photon detection efficiency remains poor and unchanged. This is due to the continued reliance on parallel-hole collimators first introduced in 1964. These collimators possess poor geometric efficiency. Here we present the performance evaluation results of a newly designed multipinhole collimator with 20 pinhole apertures (PH20) for commercial SPECT systems. Computer simulations and numerical observer studies were used to assess the noise, bias and diagnostic imaging performance of a PH20 collimator in comparison with those of a low energy high resolution (LEHR) parallel-hole collimator. Ray-driven projector/backprojector pairs were used to model SPECT imaging acquisitions, including simulation of noiseless projection data and performing MLEM/OSEM image reconstructions. Poisson noise was added to noiseless projections for realistic projection data. Noise and bias performance were investigated for five mathematical cardiac and torso (MCAT) phantom anatomies imaged at two gantry orbit positions (19.5 and 25.0 cm). PH20 and LEHR images were reconstructed with 300 MLEM iterations and 30 OSEM iterations (ten subsets), respectively. Diagnostic imaging performance was assessed by a receiver operating characteristic (ROC) analysis performed on a single MCAT phantom; however, in this case PH20 images were reconstructed with 75 pixel-based OSEM iterations (four subsets). Four PH20 projection views from two positions of a dual-head camera acquisition and 60 LEHR projections were simulated for all studies. At uniformly-imposed resolution of 12.5 mm, significant improvements in SNR and diagnostic sensitivity (represented by the area under the ROC curve, or AUC) were realized when PH20 collimators are substituted for LEHR parallel-hole collimators. SNR improves by factors of 1.94–2.34 for the five patient anatomies and two orbital positions studied. For the ROC analysis the PH20 AUC is larger than the LEHR AUC with a p-value of 0.0067. Bias performance, however, decreases with the use of PH20 collimators. Systematic analyses showed PH20 collimators present improved diagnostic imaging performance over LEHR collimators, requiring only collimator exchange on existing SPECT cameras for their use.

A Monte Carlo simulation study of the feasibility of a high resolution parallel-hole collimator with a CdTe pixelated semiconductor SPECT system

It is recommended that a pixelated parallel-hole collimator in which the hole and pixel sizes are equal be used to improve the sensitivity and spatial resolution when using a small pixel size and a single-photon emission computed tomography (SPECT) system with pixelated semiconductor detector materials (e.g., CdTe and CZT). However, some significant problems arise in the manufacturing of a pixelated parallel-hole collimator. Therefore, we sought to simulate a pixelated semiconductor SPECT system with various collimator geometric designs. The purpose of this study was to compare the quality of images generated with a pixelated semiconductor SPECT system simulated with pixelated parallel-hole collimators of various geometric designs. The sensitivity and spatial resolution of the various collimator geometric designs with varying septal heights and hole sizes were measured. Moreover, to evaluate the overall performance of the imaging system, a hot-rod phantom was designed using a Monte Carlo simulation. According to the results, the average sensitivity using a 15 mm septal height was 1.80, 2.87, and 4.16 times higher than that obtained with septal heights of 20, 25, and 30 mm, respectively. Also, the average spatial resolution using the 30 mm septal height was 44.33, 22.08, and 9.26% better than that attained with 15, 20, and 25 mm septal heights, respectively. When the results acquired with 0.3 and 0.6 mm hole sizes were compared, the average sensitivity with the 0.6 mm hole size was 3.97 times higher than that obtained with the 0.3 mm hole size, and the average spatial resolution with the 0.3 mm hole size was 45.76% better than that with the 0.6 mm hole size. We have presented the pixelated parallel-hole collimators of various collimator geometric designs and evaluations. Our results showed that the effect of various collimator geometric designs can be investigated by Monte Carlo simulation so as to evaluate the feasibility of a high resolution parallel-hole collimator with a CdTe pixelated semiconductor SPECT system.

Optimization of the angle between detector modules in a dual-head cardiac SPECT

In recent years, dedicated cardiac single photon emission computed tomography (SPECT) systems have been undergoing a profound change in design with multiple detectors and various angles between the modules to improve the sensitivity and the resolution by reducing the distance between the heart and the detector. The performance of a dual-head cardiac SPECT for small-animal imaging was characterized as a function of the angle between two detector heads by using GATE simulations, and simulation data were validated with experimental results. Each detector head consists of 50 × 50 × 6 mm3 NaI(Tl) optically coupled to a Hamamatsu H8500 position sensitive photomultiplier (PSPMT) and a low-energy high-resolution parallel-hole collimator (LEHR, septal thickness: 0.2 mm, diameter: 1.9 mm). The distance between the collimator surface and the center of rotation was set as 20, 20, 20, 25, or 31.5 mm for 70°, 80°, 90°, 100°, or 110°, respectively, based on a 40-mm field of view (FOV). A point source and a rat cardiac phantom of Tc-99m in scattering media were simulated. Projection data were acquired for 180 angular views in steps of 2° and were reconstructed by using a filtered back-projection algorithm. Results demonstrated that the angle between the detector heads did not make a big difference in the image quality when scattering media were not presented, but the dual heads in the 80° geometry provided the best spatial resolution in the cardiac phantom study. The peak-to-valley ratio between the myocardial wall and the cavity was measured as 1.87, 11.01, 3.28, 3.40, or 2.46 for 70°, 80°, 90°, 100°, or 110°, respectively. Experiments were performed with a dual-head SPECT in the 80° geometry, and the results agreed well with these from the simulations. In this study, the impact of the angle between dual detector heads on the imaging performance was evaluated, and the optimal angle was derived for a dedicated cardiac SPECT.

Comparison of Pinhole and High-Resolution Parallel-Hole Imaging for Nodular Thyroid Disease

Pinhole has been the main standard collimator to be used for thyroid imaging. There has been a gradually increasing trend to replace pinhole with the use of high-resolution low-energy parallel-hole collimator with zoom in thyroid imaging. The objective of this study is to compare parallel-hole collimator acquisition of thyroid gland with that obtained by pinhole collimator to find the effect on the diagnostic information in nodular thyroid disease. A total of 29 patients, 24 women and 5 men, aged 18 to 70 years who were routinely referred for thyroid imaging for the assessment of nodular disease were studied. Each patient was injected with 185 MBq (5 mCi) of Tc-99m sodium pertechnetate intravenously. After 20 minutes, acquisition using pinhole followed by parallel-hole collimators was obtained. For pinhole acquisition, a 3-mm insert was used, and 3 images were obtained in the anterior and anterior oblique projections. For parallel-hole acquisition, anterior view was obtained for 250 K. The collimator was placed as close as possible to the patient. The image quality, number, and definition of nodules were evaluated by 2 independent, qualified nuclear medicine physicians. Differences were resolved by consensus. There were 14 patients who had nodular patterns and 15 had no apparent nodules. There were 40 nodules of different sizes detected by pinhole imaging. Only 10 (25%) of these nodules were observed on parallel-hole images. Pinhole imaging must be used for thyroid imaging particularly in patients suspected of having nodular disease.

Improved Delineation of Parathyroid Lesions in Patients with Chronic Renal Failure Using Magnified Pinhole Imaging

(99m)Tc-sestamibi dual-phase scintigraphy is currently established for parathyroid localization. However, the imaging technique is not standardized, and the role of the pinhole collimator, especially, is not fully recognized in the imaging protocol. The aim of this study was to check whether the use of a pinhole collimator in parathyroid scintigraphy would enhance lesion detectability and delineation more than does a parallel-hole collimator or SPECT in patients with secondary hyperparathyroidism due to chronic renal failure with a mixed pattern of abnormalities. Thirty-five patients referred for a parathyroid scan were included. Imaging was performed at 10 min and 2 h after injection of 925 MBq (25 mCi) of (99m)Tc-sestamibi using both a pinhole collimator and a high-resolution parallel-hole collimator fitted to a scintillation camera. SPECT was also performed at 1.5 h after injection. The images were reviewed by 2 experienced nuclear medicine physicians, and the results were analyzed. In addition, the contrast of visualized lesions was evaluated. Twenty-three patients (65.7%) had abnormal scan findings. The McNemar test revealed better detection of parathyroid lesions using pinhole imaging than with planar parallel-hole imaging and SPECT (P < 0.001 and P < 0.03, respectively). Both observers showed good agreement in evaluating different imaging techniques (κ = 0.76). Observers were in favor of pinhole imaging because SPECT suffered from noise. Lesion contrast was significantly higher in pinhole imaging than in parallel-hole imaging and SPECT (P < 0.05), with a 16% and 11% improvement in contrast, respectively. Pinhole imaging better delineates and detects lesions in parathyroid scintigraphy than does parallel-hole imaging and SPECT. Pinhole imaging increases confidence in image interpretation because of high lesion contrast and better magnification and resolution. The use of this technique is therefore recommended as part of the routine imaging protocol for (99m)Tc-sestamibi parathyroid scintigraphy.

Performance evaluation of a multi-pinhole collimator with vertical septa

The authors have previously reported a simulation study on a novel multi-pinhole (MP) collimator that is able to provide improved angular sampling and an enlarged imaging field of view (FOV) when compared to a low-energy high-resolution parallel-hole (LEHR) collimator using a detector of equivalent size. The aim of this study was to develop a miniature single photon emission computerized tomography (SPECT) to verify the performance of the proposed MP collimator with lead vertical septa. A detector with a 70 mm×70 mm active area that consisted of a 6 mm-thick NaI(Tl) crystal coupled to a 127 mm-diameter position-sensitive photomultiplier tube (PSPMT) was used. A 7×7 pinhole collimator with a 2 mm-diameter pinhole and a focal length of 40 mm was fabricated to evaluate the performance as compared to a typical LEHR collimator. Additionally, a detector having a 50 mm×50 mm active area with 5×5 pinhole and LEHR collimators was investigated to evaluate the enlarged imaging FOV. Planar spatial resolution, sensitivity, and resolution for hot- and cold-rod phantom images were acquired. Images were reconstructed using a dedicated maximum likelihood expectation maximization (MLEM) algorithm with an unmatched projector/backprojector pair. The spatial resolution and sensitivity obtained with both collimators were 4.7 mm FWHM and 0.25 cps/μCi at a distance of 60 mm, respectively. Although the detector size was smaller than the phantom, the MP collimator allowed for imaging of the entire phantom while the image obtained with LEHR collimator suffered from a truncation artifact. The reconstructed images, using 60 and 30 projections with both 7×7 pinhole and LEHR collimators, yielded an image of similar quality to that, which was constructed using 120 projections. However, the images reconstructed with 10 projections using a 7×7 pinhole collimator showed better quality than those that used an LEHR collimator. The reconstructed images that used the MP collimator provided high-quality images with an enlarged imaging FOV, even when insufficient angular sampling data were used, which would be of use in the development of a stationary SPECT.

A SPECT Scanner for Rodent Imaging Based on Small-Area Gamma Cameras

We developed a cost-effective SPECT scanner prototype (rSPECT) for in vivo imaging of rodents based on small-area gamma cameras. Each detector consists of a position-sensitive photomultiplier tube (PS-PMT) coupled to a 30 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\, \times \,$</tex></formula> 30 NaI(Tl) scintillator array and electronics attached to the PS-PMT sockets for adapting the detector signals to an in-house developed data acquisition system. The detector components are enclosed in a lead-shielded case with a receptacle to insert the collimators. System performance was assessed using <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{99{\rm m}}{\rm Tc}$</tex></formula> for a high-resolution parallel-hole collimator, and for a 0.75-mm pinhole collimator with a 60 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}$</tex> </formula> aperture angle and a 42-mm collimator length. The energy resolution is about 10.7% of the photopeak energy. The overall system sensitivity is about <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$3~{\rm cps}/\mu {\rm Ci/detector}$</tex></formula> and planar spatial resolution ranges from 2.4 mm at 1 cm source-to-collimator distance to 4.1 mm at 4.5 cm with parallel-hole collimators. With pinhole collimators planar spatial resolution ranges from 1.2 mm at 1 cm source-to-collimator distance to 2.4 mm at 4.5 cm; sensitivity at these distances ranges from 2.8 to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$0.5~{\rm cps}/\mu {\rm Ci/detector}$</tex></formula> . Tomographic hot-rod phantom images are presented together with images of bone, myocardium and brain of living rodents to demonstrate the feasibility of preclinical small-animal studies with the rSPECT.

Development of an ultra-high resolution SPECT system with a CdTe semiconductor detector

The aim of this work was to evaluate an ultra-high spatial resolution SPECT system with a semiconductor detector and a high-resolution parallel-hole collimator or a pinhole collimator for small animal imaging. We evaluated an ultra-high spatial resolution SPECT system with a high-resolution parallel-hole collimator attached to a cadmium telluride (CdTe) semiconductor detector for small animal imaging. The sizes of an active area and a pixel in the semiconductor detector were 44 x 44 and 0.5 x 0.5 mm(2), respectively. In the high-resolution parallel-hole collimator the size of a hole was 0.4 x 0.4 mm(2), the thickness of a septum 0.1 mm, and the hole-length 30 mm. We also used a high-resolution pinhole collimator with a hole size of 0.3 or 0.5 mmvarphi. The physical performance of this SPECT system was evaluated with some experiments with phantoms filled with (99m)Tc-pertechnatate solution. In addition ideal performance and limitations of the system were evaluated with Monte Carlo simulations under the same geometrical conditions as in the experiments. In the evaluation for small animal imaging, we used mice that were administered with (99m)Tc-MDP. We also conducted an ultra-high resolution X-ray CT of the mice to verify the accumulated location of (99m)Tc-MDP using the bone CT images of the mice. The results of the phantom experiments showed that we could resolve 1 mmvarphi hot-channels and 1.6 mmvarphi cold-rods with the high-resolution parallel-hole collimator and pinhole collimators. We could image 0.3 mmvarphi hot-channels with the high-resolution pinhole collimators. The results of the simulations showed that the resolution limit in the pinhole imaging was about 0.6 mm FWHM. And the results of experiments with mice showed that we could reconstruct high-resolution images of (99m)Tc-MDP. Furthermore, the distribution of (99m)Tc-MDP in a mouse was found to correspond closely to the location of the bones of the mouse in reconstructions made with the ultra-high resolution X-ray CT system. Our results demonstrated that the ultra-high spatial resolution SPECT system was feasible for small animal imaging allowing a relatively long data acquisition time.

Imaging performance comparison between a scintillator based and a CdTe semiconductor based photon counting compact gamma camera

The authors report on the performance of two small field of view, compact gamma cameras working in single photon counting in planar imaging tests at 122 and 140 keV. The first camera is based on a LaBr3: Ce scintillator continuous crystal (49 x 49 x 5 mm3) assembled with a flat panel multianode photomultiplier tube with parallel readout. The second one belongs to the class of semiconductor hybrid pixel detectors, specifically, a CdTe pixel detector (14 x 14 x 1 mm3) with 256 x 256 square pixels and a pitch of 55 microm, read out by a CMOS single photon counting integrated circuit of the Medipix2 series. The scintillation camera was operated with selectable energy window while the CdTe camera was operated with a single low-energy detection threshold of about 20 keV, i.e., without energy discrimination. The detectors were coupled to pinhole or parallel-hole high-resolution collimators. The evaluation of their overall performance in basic imaging tasks is presented through measurements of their detection efficiency, intrinsic spatial resolution, noise, image SNR, and contrast recovery. The scintillation and CdTe cameras showed, respectively, detection efficiencies at 122 keV of 83% and 45%, intrinsic spatial resolutions of 0.9 mm and 75 microm, and total background noises of 40.5 and 1.6 cps. Imaging tests with high-resolution parallel-hole and pinhole collimators are also reported.

Design for a high-resolution small-animal SPECT system using pixellated Si(Li) detectors for in vivo /sup 125/I imaging

We propose a design for a high-resolution SPECT system for in vivo /sup 125/I imaging in small animal using pixelated lithium-drifted silicon (Si(Li)) detectors. The detectors have high detection efficiency (>90%), good energy resolution (<15% FWHM), and good intrinsic spatial resolution (/spl sim/1 mm FWHM). The SPECT system has a dual head detector geometry with the distance between the detectors ranging 30-50 mm to allow for the shortest imaging distance between the mouse and the detectors. The detectors, each with an active area of 64 mm/spl times/40 mm (64/spl times/40 array of 1 mm/sup 2/ pixels and a 6 mm thick Si(Li) detector), are mounted on a rotating gantry with an axial field-of-view of 64 mm. Using a high-resolution parallel-hole collimator, the expected spatial resolution is 1.6 mm FWHM at an imaging distance of 20 mm, and sensitivity is 6.7 cps//spl mu/Ci. /sup 125/I is a readily available radioisotope with a long half-life of 59.4 days and it is commonly used to label biological compounds in molecular biology. Conventional gamma cameras are not optimized to detect the low emission energies (27 to 35 keV) of /sup 125/I. However, Si(Li) detector provides an ideal solution for detecting the low-energy emissions of /sup 125/I. In addition, a SPECT system based on Si(Li) detector can potentially be less expensive than other detector technology because of its ease of operation and the availability of many resources for processing silicon. This will increase the availability of small-animal SPECT systems in biomedical research, thereby providing an important tool to facilitate the research in mouse biology.

Quantitative analysis for assessing regional function of liver by using 99mTc-GSA SPECT.

In the present study, we developed quantitative index for evaluating regional liver function using 99mTc diethylenetriamine-pentaacetic acid galactosyl human serum albumin (GSA). A three head SPECT equipped with a low energy high resolution parallel hole collimator was used. Used pre-filter was Butterworth and axial images were reconstructed by a ramp filter without attenuation correction. Correlation between SPECT counts and net concentration of activity of radioisotopes was evaluated in basic consideration using LKS and Nine-Ball phantoms. SPECT Counts = 0.6 x RI concentration. There was a simple correlation among GSA receptor amounts (Cr), injected GSA amounts (S), free GSA amounts (Cf), and intra hepatic receptor ratio ((Cr ratio)). Cr = S - Cf. (Cr ratio) = Cr/S, 0 < (Cr ratio) < 1. Injected GSA amounts can be calculated from injected net RI counts. Free GSA amounts can be evaluated from counts of the heart. GSA receptor amounts can be assumed by performing SPECT three times in series. Regional GSA receptor amounts can be evaluated from the ratio between the region's counts and whole counts. In clinical SPECT images, we could evaluate the regional GSA receptor amounts before and after chemolipiodolization. In conclusion, our method is a simple quantitative index of analyzing regional GSA receptor amounts.

Performance evaluation of a hand-held, semiconductor (CdZnTe)-based gamma camera.

We have designed and developed a small field of view gamma camera, the eZ SCOPE, based on use of a CdZnTe semiconductor. This device utilises proprietary signal processing technology and an interface to a computer-based imaging system. The purpose of this study was to evaluate the performance of the eZ scope in comparison with currently employed gamma camera technology. The detector is a single wafer of 5-mm-thick CdZnTe that is divided into a 16x16 array (256 pixels). The sensitive area of the detector is a square of dimension 3.2 cm. Two parallel-hole collimators are provided with the system and have a matching (256 hole) pattern to the CdZnTe detector array: a low-energy, high-resolution parallel-hole (LEHR) collimator fabricated of lead and a low-energy, high-sensitivity parallel-hole (LEHS) collimator fabricated of tungsten. Performance measurements and the data analysis were done according to the procedures of the NEMA standard. We also studied the long-term stability of the system with continuous use and variations in ambient temperature. Results were as follows. INTRINSIC ENERGY RESOLUTION: 8.6% FWHM at 141 keV.LINEARITY: There was excellent linearity between the observed photopeaks and the known gamma ray energies for the given isotopes. INTRINSIC SYSTEM UNIFORMITY: For the central field of view, the integral uniformity and the differential uniformity were, respectively, 1.6% and 1.3% with the LEHR collimator and 1.9% and 1.2% with the LEHS collimator. SYSTEM SPATIAL RESOLUTION: The FWHM measurements made at the surface of the collimator were 2.2 mm (LEHR) and 2.9 mm (LEHS).CONTRAST TEST: The average S/N ratios (i.e. counts in the irradiated pixel divided by counts in the surrounding pixels) for the inner ring pixels (8)/outer ring pixels (16) using the LEHS collimator and LEHR collimator were 3.2%/0.2% and 3.7%/0.3%, respectively. COUNT RATE CHARACTERISTICS: We could not determine the maximum count rate and the 20% loss count rate from these data because the plateau was not reached while using the solutions measured. SYSTEM SENSITIVITY: The average acquisitions were 11,052 cpm/MBq (LEHR) and 28,590 cpm/MBq (LEHS). TEMPERATURE DEPENDENCE: The system displayed minimum corresponding shift in cps with temperature changes in the measured temperature range. We designed and developed a semiconductor-based gamma camera using CdZnTe. The basic performance of this camera compares favourably with the existing gamma camera technology that is deployed in the medical field today. The most significant differences include the spatial resolution, sensitivity, high count rate characteristics and energy resolution. We believe that this device will be of value for a number of clinical applications including sentinel node detection and radiopharmaceutical-guided surgery.