Low-energy High-resolution Parallel-hole Collimators Research Articles

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.

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.

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.

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.

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.

Thyroid uptake and scintigraphy using 99mTc pertechnetate: standardization in normal individuals.

Thyroid uptake and scintigraphy using 99mTc-pertechnetate has proven to be more advantageous than with 131I-iodide, since the images have better quality, the procedure is faster and the patient is submitted to a lower radiation dose. The purpose of this study was to standardize a simple and fast methodology for performing thyroid uptake and scintigraphy and to determine the normal values for 99mTc- pertechnetate uptake. Prospective, non-randomized. Division of Nuclear Medicine, Department of Radiology, School of Medical Sciences, Campinas State University. The study consisted of 47 normal individuals, 30 women and 17 men, with ages ranging from 19 to 61 years (mean of 33 years). The laboratory assessment of thyroid function consisted of serum dosages of ultra-sensitive thyroxin and thyrotrophin. Twenty minutes after an intravenous injection of 10 mCi (370 MBq) of 99mTc-pertechnetate, the images were obtained on a computerized scintillation camera equipped with a low-energy high-resolution parallel hole collimator. All the individuals were euthyroid both on clinical and laboratory evaluation. The baseline thyroid 99mTc-pertechnetate uptake ranged from 0.4 to 1.7%. The uptake values obtained in these normal individuals showed that 95% presented a thyroid uptake that ranged from 0.4 to 1.5% of the injected dose. The assessment of thyroid structure and function using 99mTc-pertechnetate is a simple, fast and efficient method, which could easily become a part of the routine studies in nuclear medicine laboratories.