Parallel-hole Collimator Research Articles

Optimization of Coded Aperture Radioscintigraphy for Sentinel Lymph Node Mapping

Radioscintigraphic imaging during sentinel lymph node (SLN) mapping could potentially improve localization; however, parallel-hole collimators have certain limitations. In this study, we explored the use of coded aperture (CA) collimators. Equations were derived for the six major dependent variables of CA collimators (i.e., masks) as a function of the ten major independent variables, and an optimized mask was fabricated. After validation, dual-modality CA and near-infrared (NIR) fluorescence SLN mapping were performed in pigs. Mask optimization required the judicious balance of competing dependent variables, resulting in sensitivity of 0.35%, XY resolution of 2.0 mm, and Z resolution of 4.2 mm at an 11.5-cm field of view. The findings in pigs suggested that NIR fluorescence imaging and CA radioscintigraphy could be complementary, but present difficult technical challenges. This study lays the foundation for using CA collimation for SLN mapping, and also exposes several problems that require further investigation.

Detectability of foci of radioiodine uptake in the thyroid bed and neck comparing pinhole with parallel-hole collimators

The objective of this study was to evaluate the detection of the foci of radioiodine (RAI) uptake in the thyroid bed and neck of patients with well-differentiated thyroid cancer using a pinhole collimator (PiHC) compared with either whole-body images (WBIs) or individual images obtained using a parallel-hole collimator (PaHC). A retrospective review was conducted of all RAI scans done at the Washington Hospital Center between June 2000 and December 2006 on patients who had (i) well-differentiated thyroid cancer, (ii) an RAI scan of the thyroid bed and neck before their first RAI ablation or treatment, (iii) individual spot images of the neck (II) taken using both PiHC and PaHC as part of this pretreatment scan, and (iv) WBIs taken using a PaHC. To test for significant differences between the numbers of foci detected by different methods, two sample t-tests for paired groups were used. Of the 325 patients meeting the above criteria, the mean age was 46 years (range = 15-83 years). The mean (range) number of foci identified on WBIs, IIs-PaHC, and IIs-PiHC images was 2.14 (0-8), 2.82 (0-11), and 3.32 (0-14), respectively. The total number of foci detected on WBIs, IIs-PaHC, and IIs-PiHC images was 694, 916, and 1079, respectively. The means (ranges; P values) of the differences in the number foci detected with II-PiHC versus II-PaHC and II-PiHC versus WBI-PaHC were 0.502 (-3 to 6; P < 0.001) and 1.185 (-2 to 8; P < 0.001), respectively. II-PiHCs showed additional foci of uptake relative to II-PaHCs and WBI-PaHCs in 10% (32) and 33% (108) of patients, respectively. II-PiHC showed more foci of RAI uptake in the thyroid bed and neck than either II-PaHC or WBI-PaHC. Pinhole imaging offers the potential to better identify cervical metastases, possibly modify the empiric prescribed activity of RAI, and/or provide a better baseline for future comparison.

Technetium-99m-hexamethylpropylene amine oxime lung scintigraphy findings in patients with Behçet's disease

Behçet's disease (BD) is a multisystem disorder that is characterized by vasculitis, and consists of a triad of recurrent ulcers of the oral and genital mucosa with relapsing uveitis. The prevalence of pulmonary involvement varies in the range of 1-10% in various studies, and its complications are severe and life threatening. To objectively assess the degree of pulmonary vascular endothelial damage in BD, the lung uptake, and the clearance rate of technetium-99m-hexamethylpropylene amine oxime (Tc-99m-HMPAO) were determined. Twenty-three nonsmoking patients with BD (10 female, 13 male) and 11 (six female, five male) healthy nonsmoking controls underwent Tc-99m-HMPAO lung scanning, pulmonary function tests (PFT), chest radiograph examination, contrast-enhanced spiral chest computed tomography scanning, and high-resolution computed tomography examinations. Immediately after the bolus injection of 740 MBq of Tc-99m-HMPAO posterior sequential images were obtained at 1-s intervals for 150 s and subsequent images were obtained at one frame per minute (min) over a 10-min period, using a double-headed gamma camera equipped with a low-energy all-purpose parallel hole collimator. Dynamic images were used to calculate the Tc-99m-HMPAO lung clearance rate (T1/2). Simultaneously, a static anterior image, including a large part of the liver, was obtained of 5-min duration at 10 min after the injection. Regular regions of interests were drawn over the midportion of the right lung and the highest activity area of the liver parenchyma was selected and lung/liver (L/Li) uptake ratios were calculated to represent the degree of pulmonary vascular endothelial damage. Chest radiograph, high-resolution computed tomography, and computed tomography findings in patients with BD were nonspecific for BD. There was also a statistically significant difference between patients with BD (30.26 ± 10.55 s) and normal controls (19.53 ± 6.24 s) on their T1/2 values (P = 0.0004). The results show that the L/Li ratios on the Tc-99m-HMPAO lung scan were significantly higher in patients with BD (0.60 ± 0.19) than those in normal controls (0.39 ± 0.07) (P = 0.0021). Using a cutoff value of 0.50, 15 of 23 (65%) patients with BD had increased L/Li ratios. No correlation was found between the mean T1/2 values of Tc-99m-HMPAO clearance and the PFT in patients with BD. The L/Li ratios were not correlated with PFT in patients with BD. The degree of pulmonary vascular endothelial damage was represented as increased L/Li ratios and decreased lung clearance rate measured on the Tc-99m-HMPAO lung scan in patients with BD. Our results indicated that determining the T1/2 values and the L/Li ratios on Tc-99m-HMPAO lung imaging should be an objective method to assess subclinical pulmonary damage even in the early stages of BD in the patients.

Optimization of a parallel hole collimator/CdZnTe gamma‐camera architecture for scintimammography

Small field-of-view CdZnTe (CZT) gamma cameras are increasingly studied for breast lesion detection to complement mammography or ultrasonographic findings. However, in classical collimation configurations, they remain limited by the trade-off between spatial resolution and sensitivity. The HiSens architecture was proposed to overcome these limitations. Using an accurate 3D localization of the interactions inside the detector, this architecture leads to a gain in sensitivity without loss in spatial resolution. In this article, the relevance of the HiSens architecture for planar scintimammography is studied. A detective quantum efficiency (DQE) computation method is developed and used to optimize the dimensioning of a parallel hole collimator dedicated to scintimammography. Based on the DQE curves, the impact of the collimator-to-detector distance is studied. Two algorithms are proposed to combine data acquired with different collimator-to-detector distances. It is shown that CZT detector virtual pixelization increases system sensitivity by 3.3 while preserving a standard LEHR spatial resolution. The introduction of a gap between the CZT detector and the collimator is useful to modulate the DQE curve shape. The combination of data acquired using different gaps in the image formation process leads to enhanced restoration of the frequency content of the images, resulting in image contrast and spatial resolution improvements. Acquisition duration or injected activity could be markedly reduced if the HiSens architecture with an appropriate collimator-detector gap were used.

Characterization of a rotating slat collimator system dedicated to small animal imaging

Some current investigations based on small animal models are dedicated to functional cerebral imaging. They represent a fundamental tool to understand the mechanisms involved in neurodegenerative diseases. In the radiopharmaceutical development approach, the main challenge is to measure the radioactivity distribution in the brain of a subject with good temporal and spatial resolutions. Classical SPECT systems mainly use parallel hole or pinhole collimators. In this paper we investigate the use of a rotating slat collimator system for small animal brain imaging. The proposed prototype consists of a 64-channel multi-anode photomultiplier tube (H8804, Hamamatsu Corp.) coupled to a YAP:Ce crystal highly segmented into 32 strips of 0.575 × 18.4 × 10 mm3. The parameters of the rotating slat collimator are optimized using GATE Monte Carlo simulations. The performance of the proposed prototype in terms of spatial resolution, detection efficiency and signal-to-noise ratio is compared to that obtained with a gamma camera equipped with a parallel hole collimator. Preliminary experimental results demonstrate that a spatial resolution of 1.54 mm can be achieved with a detection efficiency of 0.012% for a source located at 20 mm, corresponding to the position of the brain in the prototype field of view.

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.

Exprerimental Evaluation of a Dedicated Pinhole SPECT System for Small Animal Imaging and Scintimammography

Nuclear medicine (SPECT and PET) provides functional information, which is complementary to the structural. In cancer imaging radiopharmaceuticals allow visualization of cancer cells functionality, thus small cell population can be imaged. This allows early diagnosis, as well as fast assessment of response to therapy. Our system is a single head gamma camera based on an R3292 position sensitive photomultiplier tube (PSPMT), coupled to a 10cm in diameter CsI:Tl crystal. We have assessed two CsI:Tl crystals with pixel size of 2x2mm2 and 3x3mm2 respectively. Three collimators were tested: a) a hexagonal, 1.1mm in diameter, general purpose parallel hole collimator b) a 1mm pinhole and c) a 2mm pinhole. Systems were tested using capillary phantoms. All measurements were carried out in photon counting mode with gamma radiation produced by 99mTc. Using the 2x2mm2 crystal and the 1mm pinhole collimator - a resolution better than 1mm was achieved. This allows very detailed imaging of small animals. Using the 3x3mm2 and the 2mm pinhole collimator a resolution of 1.3mm was possible with suitable sensitivity for breast imaging. Those results indicate that this system is suitable for animal and breast studies. The next step will be clinical evaluation of the camera.

Exprerimental Evaluation of a Dedicated Pinhole SPECT System for Small Animal Imaging and Scintimammography

Nuclear medicine (SPECT and PET) provides functional information, which is complementary to the structural. In cancer imaging radiopharmaceuticals allow visualization of cancer cells functionality, thus small cell population can be imaged. This allows early diagnosis, as well as fast assessment of response to therapy. Our system is a single head gamma camera based on an R3292 position sensitive photomultiplier tube (PSPMT), coupled to a 10cm in diameter CsI:Tl crystal. We have assessed two CsI:Tl crystals with pixel size of 2x2mm 2 and 3x3mm 2 respectively. Three collimators were tested: a) a hexagonal, 1.1mm in diameter, general purpose parallel hole collimator b) a 1mm pinhole and c) a 2mm pinhole. Systems were tested using capillary phantoms. All measurements were carried out in photon counting mode with gamma radiation produced by 99m Tc. Using the 2x2mm 2 crystal and the 1mm pinhole collimator - a resolution better than 1mm was achieved. This allows very detailed imaging of small animals. Using the 3x3mm 2 and the 2mm pinhole collimator a resolution of 1.3mm was possible with suitable sensitivity for breast imaging. Those results indicate that this system is suitable for animal and breast studies. The next step will be clinical evaluation of the camera.

Simultaneous in vivo dynamic contrast-enhanced magnetic resonance and scintigraphic imaging

In this study, we investigated the in vivo application of an integrated small-animal magnetic resonance (MR) and gamma-ray imaging system that consists of a semiconductor-based radiation detector, a parallel-hole collimator, and a specialized radiofrequency coil. Gadodiamide and 99mTc sestimibi agents were injected simultaneously into a mouse, and simultaneous dynamic contrast-enhanced MR and scintigraphic images of the kidneys were acquired. The time curves of both the MR signal intensity and radioactivity indicate a rapid uptake of the agents followed by a more gradual excretion, consistent with the previously reported literature. Our results demonstrate the feasibility of measuring multiple biological processes at the same time using both MR contrast agents and radiotracers.

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.

Yttrium-90-labeled microsphere tracking during liver selective internal radiotherapy by bremsstrahlung pinhole SPECT: feasibility study and evaluation in an abdominal phantom

BackgroundThe purpose of the study is to evaluate whether a pinhole collimator is better adapted to bremsstrahlung single photon emission computed tomography [SPECT] than parallel-hole collimators and in the affirmative, to evaluate whether pinhole bremsstrahlung SPECT, including a simple model of the scatter inside the patient, could provide a fast dosimetry assessment in liver selective internal radiotherapy [SIRT].Materials and methodsBremsstrahlung SPECT of an abdominal-shaped phantom including one cold and five hot spheres was performed using two long-bore parallel-hole collimators: a medium-energy general-purpose [MEGP] and a high-energy general-purpose [HEGP], and also using a medium-energy pinhole [MEPH] collimator. In addition, ten helical MEPH SPECTs (acquisition time 3.6 min) of a realistic liver-SIRT phantom were also acquired.ResultsWithout scatter correction for SPECT, MEPH SPECT provided a significantly better contrast recovery coefficient [CRC] than MEGP and HEGP SPECTs. The CRCs obtained with MEPH SPECT were still improved with the scatter correction and became comparable to those obtained with positron-emission tomography [PET] for the 36-, 30- (cold), 28-, and 24-mm-diameter spheres: CRC = 1.09, 0.59, 0.91, and 0.69, respectively, for SPECT and CRC = 1.07, 0.56, 0.84, and 0.63, respectively, for PET. However, MEPH SPECT gave the best CRC for the 19-mm-diameter sphere: CRC = 0.56 for SPECT and CRC = 0.01 for PET. The 3.6-min helical MEPH SPECT provided accurate and reproducible activity estimation for the liver-SIRT phantom: relative deviation = 10 ± 1%.ConclusionBremsstrahlung SPECT using a pinhole collimator provided a better CRC than those obtained with parallel-hole collimators. The different designs and the better attenuating material used for the collimation (tungsten instead of lead) explain this result. Further, the addition of an analytical modeling of the scattering inside the phantom resulted in an almost fully recovered contrast. This fills the gap between the performance of90Y-PET and bremsstrahlung pinhole SPECT which is a more affordable technique and could even be used during the catheterization procedure in order to optimize the90Y activity to inject.

Performance study of a fan beam collimator designed for a multi-modality small animal imaging device

This paper describes the methodology to design and conduct the performances of a fan beam collimator. This fan beam collimator was designed to use with a multi-modality small animal imaging device and the performance of the collimator was studied for a 3D geometry. Analytical expressions were formulated to calculate the parameters for the collimator. A Monte Carlo model was developed to analyze the scattering and image noises for a 3D object. The results showed that the performance of the fan beam collimator was strongly dependent on the source distribution and position. The fan beam collimator showed increased counting efficiency in comparison to a parallel hole collimator. Inside attenuating medium, the increased attenuating effect outweighed the fan beam increased counting efficiency.

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.

Effect of acute cold exposure on lung perfusion and tracheal smooth muscle contraction in rabbit

Acute exposure to cold temperature can affect the respiratory system of those exposed to extreme weather and induces asthma in asthmatic patients. However, the effect on lung perfusion and the pulmonary circulation was not addressed in any previous study. The present study investigates the effects of acute cold exposure on tracheal smooth muscle and lung perfusion. New Zealand White rabbits were used in these experiments. For in vitro experiments, isolated tracheal segments were suspended in organ baths containing Krebs' solution for isometric tension recording. Tissue response to cooling from 37 to 4°C was examined. For in vivo experiments, the rabbits were kept in a cold room (4°C) for 1h. Lung perfusion scintigraphy was performed at the end of this period. Each rabbit was injected with 74MBq (2mCi) technetium-99m macroaggregated ((99m)Tc MAA). Perfusion studies were done by using Gamma camera equipped with a low-energy, high-resolution, parallel-hole collimator interfaced with a computer. Static images were acquired 5min after administration of the radiotracer. Cooling induced a rapid and reproducible contraction in the tracheal smooth muscle. Rabbits exposed to cold temperature had lesser lung perfusion than controls using radionuclide perfusion study. Our results highlight the response of tracheal muscle and pulmonary circulation to cold exposure. These results indicate that cooling induced contraction of the trachea and decreased pulmonary circulation and lung perfusion. This summation of acute cooling for tracheal smooth muscle and pulmonary circulation seems to be the reason for the severe cooling-induced contraction.

Solid-State SPECT technology: fast and furious

This traditionaldesign uses a thallium-doped sodium iodine crystalwhich scintillates in response to gamma photons, pro-ducing weak flash of light, coupled with a set ofphotomultiplier tubes which detect the fluorescent flash.A parallel-hole collimator filters the incident gammarays so that only those traveling approximately parallelto a specified direction are allowed through. This designof the conventional gamma camera suffers from severalmajor limitations, compromising its performance. Thephoton energy resolution is limited due to the physicalcharacteristics of the NaI crystal and photomultipliers,while the spatial resolution is reduced due to the geo-metric characteristics of the collimator and limitednumber of photomultipliers. The sensitivity of thecamera system is very low since the low-energy high-resolution collimator attenuates the overwhelmingmajority ([99.9%) of the incident photons. Thesetechnological limitations lead to relatively a largeamount of administered radiation doses, and/or pro-longed imaging time. Furthermore, the photomultipliertube technology results in a large, bulky camera head,requiring large laboratory space and dictating inconve-nient patient position.A major aim in nuclear cardiology to date has beento achieve reducing patient radiation exposure andimaging time, while improving image quality and thusdiagnostic precision. The use of dual-detector SPECTcameras resulted in 50% or greater reduction in imagingtime, and the use of iterative reconstruction algorithmswith resolution recovery provided additional reductionin acquisition time, without compromising resolution.

Poster - Thur Eve - 74: A Fan-Beam Collimator Design for Small Animal Scintigraphy

The objective of the study was to design and conduct a performance study of a fan‐beam collimator for a multi‐modality small‐animal imaging device, which was primarily responsible yielding high‐resolution images with high sensitivity ‐ a necessity for rapid dynamic studies. The device had of a high‐resolution gamma camera that included a 2×2 array of position sensitive photomultiplier tubes and a pixilated NaI(Tl) scintillator array. The collimator's holes were square‐shaped to match the layout of the scintillation detector, with a septal thickness equals t the separation between two consecutive pixel elements. The collimator septal length (l), focal length (f), and septal thickness (t) were calculated. A Monte Carlo model was used to calculate the scattering and noise photons for a homogeneous 3D attenuating medium. The detector pixels were defined as repeated structures of square shaped NaI(Tl) crystal blocks (0.6 cm thick). The outer layer of the detector blocks was surrounded by vacuum to stop external scattering. The collimator was defined as intersecting tungsten plates of thickness 0.02cm each. The angular dependency of the fan‐beam collimator was studied and a signal to noise index was calculated within the central field of view. The detection efficiency of the fan‐beam collimator increased significantly (about 10 2 times more) in comparison to the parallel hole collimator when a point source was placed close to the focal point. The angular effect on the fan‐beam performance showed a minor effect in comparison to that of attenuation effect. The use of the fan‐beam collimator significantly increased the detection efficiency for the gamma camera.

MO‐E‐204C‐02: Bedside SPECT Imaging with Pinhole Collimation

Purpose: The objective of this study is to evaluate the imaging performance of a mobile SPECT system with a pinhole collimator and compare the results with parallel hole collimators. The goal is to obtain both planar and tomographic performance measures with Tc‐99m and F‐18. This abstract presents the results using Tc‐99m. Method and Materials: The system utilizes a small field of view camera with pixilated NaI crystal and position‐sensitive photomultiplier tubes. The pinhole collimator is a tungsten knife edge with a hole diameter of 3mm, a focal length of 12.5cm, and an acceptance angle of 90 degrees. The parallel hole collimators have been previously described along with their imaging performance evaluation [1]. The following performance measures with the pinhole collimator were obtained and are presented here: count rate performance, energy resolution, flood field uniformity, system spatial resolution, system sensitivity. Results: The maximum count rate was calculated to be 1.58×105 cps corresponding to an activity of 161 μCi at 30cm. An energy spectrum from the flood acquisition demonstrated an energy resolution of 20% FWHM. Magnification corrected, system planar spatial resolution was 1.03 cm with a system sensitivity of 1.39 cps/μCi at a source to collimator distance of 10 cm. Conclusion: The imaging performance of a mobile SPECT system with a pinhole collimator has been presented. In comparison to parallel hole collimation, the pinhole collimator provides superior spatial resolution and sensitivity at distances less than 5cm. However, at further distances, pinhole sensitivity declines while parallel hole sensitivity remains relatively constant. Research sponsored by the United States Army Medical Research and Material Command under Award No. W81XWH‐04‐1‐0594

SU‐GG‐I‐180: Application of Molecular Imaging in the Monitoring of Angiogenesis of a Hindlimb Ischemia Model

Purpose: Avβ3 integrin expression is a characteristic feature of the angiogenic phenotype of endothelial cells. Targeted molecular imaging of integrins may be a further step forward in the evaluation of specific and early aspects of angiogenesis. The purpose of our study was to investigate the potential of molecular imaging with the aid of a dedicated high resolution γ camera in the rabbit hindlimb ischemia model. Method and Materials: A 99mTc labeled cyclic RGD peptide ([c RGDfk‐His]‐99mTc) was employed for angiogenesis imaging in the New Zealand white rabbits hindlimb ischemia model. Imaging of αvβ3 expression was performed in two animal groups. In group A imaging was employed 3 days and in group B 9 days post femoral artery occlusion (2 rabbits in each group). Each rabbit was injected intravenously with 200 μl of [c RGDfk‐His]‐99mTc (0.5 mCi). Consequently dynamic planar imaging was performed with a high resolution gamma camera with FOV 5×10 cm, equipped with a parallel hole collimator. Static 8 minute images at 80 minutes post injection of the radiotracer were acquired. Results: We have imaged 4 rabbits. An increase of 12.2% was observed in group A in relative radiotracer retention at the ischemic hindlimb compared to control. In group B this relative radiotracer retention was increased to 25.8%. The control limbs showed an increase in the radiotracer retention at day 9 but still much lower compared to ischemic limbs. Moreover, radiotracer accumulation was observed to a region distal to the original area of occlusion, where the newly formed proximal collaterals are located. Conclusion: Our study demonstrates that the phenomenon of angiogenesis proceeds and is maximized within on day 9 following induction of ischemia in a mammalian experimental model. Further studies are deemed necessary in order to establish this conclusion and provide quantitative results.

IMAGE OPTIMIZATION IN SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY BY HARDWARE MODIFICATIONS WITH MONTE CARLO SIMULATION

Introduction: In Single Photon Emission Computed Tomography (SPECT), the projection data used for image reconstruction are distorted by several factors, including attenuation and scattering of gamma rays, collimator structure, data acquisition method, organ motion, and washout of radiopharmaceuticals. All these make reconstruction of a quantitative SPECT image very difficult. Simulation of a SPECT system is a convenient method to assess the impact of these factors on the image quality. Materials and Methods: The SIMIND Monte Carlo program was employed to simulate a Siemens E.CAM SPECT system. Verification of the simulation was performed by comparing the performance parameters of the system. The verified system was used for SPECT simulations of homogenous and inhomogeneous voxelized phantoms in conjugation with hardware modifications. The resulting data were compared with those obtained from the simulated system without any modifications. Image quality was assessed by comparing the Structural SIMularity index (SSIM), contrast, and resolution of images. Results: The energy spectra acquired from both simulated and real SPECT systems demonstrated similar energy peak regions. The resulting full-widths-at-half-maximums were 13.92 keV for the simulation and 13.58 keV for experimental data, corresponding to energy resolutions of 9.95% and 9.61%, and with calculated sensitivities of 85.39 and 85.11 cps/MBq, respectively. Better performance parameters were obtained with a hardware-modified system constructed using a 0.944 cm thickness NaI(Tl) crystal covered by a layer of 0.24 cm aluminum, a slat of 4.5 cm Pyrex as a backscattering medium, and a parallel hole collimator of Pb-Sb alloy with 2.405 cm thickness. Conclusion: The modeling of a Siemens E.CAM SPECT system was performed with the SIMIND Monte Carlo code. Results obtained with the code are in good agreement with experimental results. The findings demonstrate that the proposed hardware modifications in the system appear to be suitable for further improvement of the performance parameters of the system, indicating that future investigations can be conducted on using the system for supplementary studies on image improvement in the field of nuclear medicine.

High-Resolution Versus High-Sensitivity SPECT Imaging With Geometric Blurring Compensation for Various Parallel-Hole Collimation Geometries

Recent studies have shown that trading efficiency for improved resolution may be a good choice for small lesion detection, but utilizing collimator with high efficiency may be more favorable for cardiac single photon emission computed tomography (SPECT). This paper investigates the tradeoffs of geometric-blurring compensation for high-resolution (HR) and high-sensitivity (HS) SPECT imaging with various parallel-hole collimators in terms of noise reduction and resolution recovery. Five types of collimators were investigated and compared with a general all purpose collimator using computer simulations. It is shown that less noisy SPECT images can be achieved with unchanged spatial resolution using large collimator holes with blurring compensation. The optimal collimator hole found in the computer simulation is the one with a hole acceptance angle in the range from 6.3 degrees to 9.4 degrees. Phantom experiments with two cardiac-insert phantoms show that the resolution of the image obtained using the HS collimator can be successfully recovered by blurring compensation, and the image is less noisy compared to the one obtained using the HR collimator.