Detector Collimation Research Articles

Imaging of Arthroplasties: Improved Image Quality and Lesion Detection With Iterative Metal Artifact Reduction, a New CT Metal Artifact Reduction Technique.

The purpose of this study was to compare iterative metal artifact reduction (iMAR), a new single-energy metal artifact reduction technique, with filtered back projection (FBP) in terms of attenuation values, qualitative image quality, and streak artifacts near shoulder and hip arthroplasties and observer ability with these techniques to detect pathologic lesions near an arthroplasty in a phantom model. Preoperative and postoperative CT scans of 40 shoulder and 21 hip arthroplasties were reviewed. All postoperative scans were obtained using the same technique (140 kVp, 300 quality reference mAs, 128 × 0.6 mm detector collimation) on one of three CT scanners and reconstructed with FBP and iMAR. The attenuation differences in bones and soft tissues between preoperative and postoperative scans at the same location were compared; image quality and streak artifact for both reconstructions were qualitatively graded by two blinded readers. Observer ability and confidence to detect lesions near an arthroplasty in a phantom model were graded. For both readers, iMAR had more accurate attenuation values (p < 0.001), qualitatively better image quality (p < 0.001), and less streak artifact (p < 0.001) in all locations near arthroplasties compared with FBP. Both readers detected more lesions (p ≤ 0.04) with higher confidence (p ≤ 0.01) with iMAR than with FBP in the phantom model. The iMAR technique provided more accurate attenuation values, better image quality, and less streak artifact near hip and shoulder arthroplasties than FBP; iMAR also increased observer ability and confidence to detect pathologic lesions near arthroplasties in a phantom model.

Design and assessment of a novel SPECT system for desktop open-gantry imaging of small animals: A simulation study.

Given increasing efforts in biomedical research utilizing molecular imaging methods, development of dedicated high-performance small-animal SPECT systems has been growing rapidly in the last decade. In the present work, we propose and assess an alternative concept for SPECT imaging enabling desktop open-gantry imaging of small animals. The system, PERSPECT, consists of an imaging desk, with a set of tilted detector and pinhole collimator placed beneath it. The object to be imaged is simply placed on the desk. Monte Carlo (MC) and analytical simulations were utilized to accurately model and evaluate the proposed concept and design. Furthermore, a dedicated image reconstruction algorithm, finite-aperture-based circular projections (FABCP), was developed and validated for the system, enabling more accurate modeling of the system and higher quality reconstructed images. Image quality was quantified as a function of different tilt angles in the acquisition and number of iterations in the reconstruction algorithm. Furthermore, more complex phantoms including Derenzo, Defrise, and mouse whole body were simulated and studied. The sensitivity of the PERSPECT was 207 cps/MBq. It was quantitatively demonstrated that for a tilt angle of 30°, comparable image qualities were obtained in terms of normalized squared error, contrast, uniformity, noise, and spatial resolution measurements, the latter at ∼0.6 mm. Furthermore, quantitative analyses demonstrated that 3 iterations of FABCP image reconstruction (16 subsets/iteration) led to optimally reconstructed images. The PERSPECT, using a novel imaging protocol, can achieve comparable image quality performance in comparison with a conventional pinhole SPECT with the same configuration. The dedicated FABCP algorithm, which was developed for reconstruction of data from the PERSPECT system, can produce high quality images for small-animal imaging via accurate modeling of the system as incorporated in the forward- and back-projection steps. Meanwhile, the developed MC model and the analytical simulator of the system can be applied for further studies on development and evaluation of the system.

Prediction of Beef Fat Content Simultaneously under Static and Motion Conditions Using near Infrared Spectroscopy

Fat content is one of the most important quality indicators for minced beef products. In this study, a multipoint near infrared (NIR) spectrophotometer system, based on a Fabry–Perot interferometer, combined with a four-point photodiode array detector and flexible collimator–probe arrangement, was used for real-time analysis of beef fat content. The system was employed to predict fat content of mixed minced beef samples concurrently under two different conditions: (a) static and slow motion and (b) static and fast motion. Additionally, a separate measurement was conducted to further test the independency of a collimator–probe arrangement by scanning two samples with different fat percentages concurrently under static and motion conditions. Partial least squares regression was employed, obtaining coefficients of determination in calibration ( R2c) of 0.95, confirming a good fit for the three models. The fat contents of samples in the independent set were predicted with reasonable accuracy: r2 in the range 0.82–0.92 and standard error of prediction in the range 3.05–3.98%. Moreover, the spectral features observed for the probe independency test clearly illustrated the flexibility and independency of the collimator–probe arrangement. This study showed that the multipoint NIR spectroscopy system can predict beef fat content concurrently under static and motion conditions and illustrates its potential use as an in-line monitoring tool at various junctions in a meat processing plant.

A Cardiac SPECT System with Multiple Collimated Detectors Rotating in an Elliptical Orbit

A Cardiac SPECT System with Multiple Collimated Detectors Rotating in an Elliptical Orbit The cardiac SPECT is a good study because of the large clinical demand and the need for improved image quality. SPECT imaging usually suffers from poor spatial resolution and high statistical noise due to patient radiation safety concerns. Based on an emission imaging device shaped as an arc in the form of a part of an ellipse with multiple collimated detector columns, a new cardiac SPECT system in an elliptical orbit (EO-SPECT) is proposed to improve the geometric efficiency and the spatial resolution.

Note: Detector collimators for the nanoscale ordered materials diffractometer instrument at the Spallation Neutron Source.

Five neutron collimator designs were constructed and tested at the nanoscale ordered materials diffractometer (NOMAD) instrument. Collimators were made from High Density PolyEthylene (HDPE) or 5% borated HDPE. In all cases, collimators improved the signal to background ratio and reduced detection of secondary scattering. In the Q-range 10-20 Å(-1), signal to background ratio improved by factors of approximately 1.6 and 2.0 for 50 and 100 mm deep collimators, respectively. In the Q-range 40-50 Å(-1), the improvement factors were 1.8 and 2.7. Secondary scattering as measured at Q ∼ 9.5 Å(-1) was significantly decreased when the collimators were installed.

Experimental and simulated study of detector collimation for a portable 3″ × 3″ NaI(Tl) detector system for in-situ measurements

The effect of detector collimator and scatterer thickness on multiple Compton backscattered gamma photons is studied. Gamma photons from a 137Cs source of 5.8 mCi, is allowed to fall on Carbon, Aluminium, Iron and Copper targets and the scattered photons are detected by a properly shielded 76 mm × 76 mm NaI(Tl) scintillation detector located at 90° to the incident beam. To extract the contribution of multiple scattered photons from the measured spectra, single scattered distribution is remodelled analytically. The thickness at which the multiple scattered photons saturate is determined for different detector collimator apertures and scatterer thicknesses. The variation of saturation thickness, Signal-to-Noise (S/N) ratio, Multiple Scattering Fraction (MSF) for different materials and collimator sizes are studied and compared with the available literature. Monte Carlo simulated calculations using MCNP code supports the present experimental work.

Collimator Design for a Brain SPECT/MRI Insert

This project’s goal is to design a SPECT insert for a clinical MRI system for simultaneous brain SPECT/MR imaging, with a high-sensitivity collimator and high-resolution detectors. We have compared eight collimator designs, four multi-pinhole and four multi-slit slit-slat configurations. The collimation was designed for a system with rings of 25 $5\times 5~\hbox{cm}$ detectors. We introduce the concept of 1/2-pinhole and 1/2-slit, which are transaxially shared between two adjacent detectors. Analytical geometric efficiency was calculated for an activity distribution corresponding to a human brain and a range of intrinsic detector resolutions ${\rm R}_i$ and target resolutions ${\rm R}_t$ at the centre of the FOV. Noise-free data were simulated with and without depth-of-interaction (DOI) information, 0.8 mm ${\rm R}_i$ and 10 mm ${\rm R}_t$ FWHM, and reconstructed for uniform, Defrise, Derenzo, and Zubal brain phantoms. Comparing the multi-pinhole and multi-slit slit-slat collimators, the former gives better reconstructed uniformity and transaxial resolution, while the latter gives better axial resolution. Although the $2 \times 2$ -pinhole and 2-slit designs give the highest sensitivities, they result in a sub-optimal utilisation of the detector FOV. The best options are therefore the $ 5+ 2 1/2$ -pinhole and the $1 + 2 1/2$ -slit systems, with sensitivities of $1.8 \times {10^{ - 4}}$ and $3.2 \times {10^{ - 4}}$ , respectively. Noiseless brain phantom reconstructions with the multi-pinhole collimator are slightly superior as compared to slit-slat, in terms of symmetry and accuracy of the activity distribution, but the same is not true when noise is included. DOI information reduces artefacts and improves uniformity in geometric phantoms. Further evaluation is needed with prototype collimators.

Suspected Pulmonary Thromboembolism and Deep Venous Thrombosis: A Comprehensive 64-slice Multidetector Computed Tomography Diagnosis in Gynecologic Patients.

Suspected Pulmonary Thromboembolism and Deep Venous Thrombosis: A Comprehensive 64-slice Multidetector Computed Tomography Diagnosis in Gynecologic Patients.

Optimising the neutron environment of Radiation Portal Monitors: A computational study

Efficient and reliable detection of radiological or nuclear threats is a crucial part of national and international efforts to prevent terrorist activities. Radiation Portal Monitors (RPMs), which are deployed worldwide, are intended to interdict smuggled fissile material by detecting emissions of neutrons and gamma rays. However, considering the range and variety of threat sources, vehicular and shielding scenarios, and that only a small signature is present, it is important that the design of the RPMs allows these signatures to be accurately differentiated from the environmental background. Using Monte-Carlo neutron-transport simulations of a model 3He detector system we have conducted a parameter study to identify the optimum combination of detector shielding, moderation, and collimation that maximises the sensitivity of neutron-sensitive RPMs. These structures, which could be simply and cost-effectively added to existing RPMs, can improve the detector response by more than a factor of two relative to an unmodified, bare design. Furthermore, optimisation of the air gap surrounding the helium tubes also improves detector efficiency.

Design, optimization and performance of source and detector collimators for gamma-ray scanning of a lab-scale distillation column

When using source and detector collimators for gamma ray column scanning, it is important to obtain an acceptable density profile quality. This paper consists of two main works. The first is devoted to describing the designs used to optimize the source and detector collimators for a lab-scale distillation column, and the second is devoted to investigating the effect of designed collimators on the quality of the density profiles obtained using the gamma scanning technique. Simulations using the MCNP4C Monte Carlo code were performed to model the collimators and obtain the density profiles. The source and detector collimator designs were developed for a cylindrical volume source with the energy of 0.662MeV and 1in.×1in. NaI, respectively. The pinhole and panoramic collimator designs and the pinhole and quartic collimator designs were considered for the source and the detector, respectively. The source container, with an opening angle of 60°, has the capability of substituting the collimator for high resolution, general and high sensitivity purposes. The pinhole collimator parameters for the source that were obtained were generally quite coarse and were 1.2cm in diameter and 4cm in length. Additionally, the detector pinhole collimator thickness and length obtained were 4cm and 5cm, respectively. Using the semi-quartic collimator for the detector, the weight of required lead was reduced by over 33% compared with the pinhole collimator.The simulation results of the column scanning in abnormal operation condition have been validated by experimental measurement results. The obtained results from scans demonstrated that the optimized panoramic source collimator and semi-quartic detector collimator in this study could help us to obtain an acceptable density profile quality in total count approach.

Improved dosimetry for targeted radionuclide therapy using nonrigid registration on sequential SPECT images.

Voxel-level and patient-specific 3D dosimetry for targeted radionuclide therapy (TRT) typically involves serial nuclear medicine scans. Misalignment of the images can result in reduced dosimetric accuracy. Since the scans are typically performed over a period of several days, there will be patient movement between scans and possible nonrigid organ deformation. This work aims to implement and evaluate the use of nonrigid image registration on a series of quantitative SPECT (QSPECT) images for TRT dosimetry. A population of 4D extended cardiac torso phantoms, comprised of three In-111 Zevalin biokinetics models and three anatomical variations, was generated based on the patient data. The authors simulated QSPECT acquisitions at five time points. At each time point, individual organ and whole-body deformation between scans were modeled by translating/rotating organs and the body up to 5°/voxels, keeping ≤5% difference in organ volume. An analytical projector was used to generate realistic noisy projections for a medium energy general purpose collimator. Projections were reconstructed using OS-EM algorithm with geometric collimator detector response, attenuation, and scatter corrections. The QSPECT images were registered using organ-based nonrigid image registration method. The cumulative activity in each voxel was obtained by integrating the activity over time. Dose distribution images were obtained by convolving the cumulative activity images with a Y-90 dose kernel. Dose volume histograms (DVHs) for organs-of-interest were analyzed. After nonrigid registration, the mean differences in organ doses compared to the case without misalignment were improved from (-15.50 ± 5.59)% to (-2.12 ± 1.05)% and (-7.28 ± 2.30)% to (-0.23 ± 0.71)% for the spleen and liver, respectively. For all organs, the cumulative DVHs showed improvement after nonrigid registration and the normalized absolute error of differential DVHs ranged from 6.79% to 22.70% for liver and 26.00% to 39.70% for spleen with different segmentation methods. These results demonstrated that nonrigid registration of sequential QSPECT images is feasible for TRT and improves the accuracy of 3D dosimetry.

3D elemental sensitive imaging by full-field XFCT.

X-ray fluorescence computed tomography (XFCT) is a stimulated emission tomography modality that maps the three-dimensional (3D) distribution of elements. Generally, XFCT is done by scanning a pencil-beam across the sample. This paper presents a feasibility study of full-field XFCT (FF-XFCT) for 3D elemental imaging. The FF-XFCT consists of a pinhole collimator and X-ray imaging detector with no energy resolution. A prototype imaging system was set up at the Shanghai Synchrotron Radiation Facility (SSRF) for imaging the phantom. The first FF-XFCT experimental results are presented. The cadmium (Cd) and iodine (I) distributions were reconstructed. The results demonstrate FF-XFCT is fit for 3D elemental imaging and the sensitivity of FF-XFCT is higher than a conventional CT system.

GATE simulation of a LYSO-based SPECT imager: Validation and detector optimization

This paper presents a small animal SPECT system that is based on cerium doped lutetium–yttrium oxyorthosilicate (LYSO) scintillation crystal, position sensitive photomultiplier tubes (PSPMTs) and parallel hole collimator. Spatial resolution test and animal experiment were performed to demonstrate the imaging performance of the detector. Preliminary results indicated a spatial resolution of 2.5mm at FWHM that cannot meet our design requirement. Therefore, we simulated this gamma camera using GATE (GEANT 4 Application for Tomographic Emission) aiming to make detector spatial resolution less than 2mm. First, the GATE simulation process was validated through comparison between simulated and experimental data. This also indicates the accuracy and effectiveness of GATE simulation for LYSO-based gamma camera. Then the different detector sampling methods (crystal size with 1.5, and 1mm) and collimator design (collimator height with 30, 34.8, 38, and 43mm) were studied to figure out an optimized parameter set. Detector sensitivity changes were also focused on with different parameters set that generated different spatial resolution results. Tradeoff curves of spatial resolution and sensitivity were plotted to determine the optimal collimator height with different sampling methods. Simulation results show that scintillation crystal size of 1mm and collimator height of 38mm, which can generate a spatial resolution of ~1.8mm and sensitivity of ~0.065cps/kBq, can be an ideal configuration for our SPECT imager design.

Optimization of a measurement facility for radioactive waste free release by Monte Carlo simulation

A novel free release measurement facility (FRMF) was developed within the joint research project “Metrology for Radioactive Waste Management” of the European Metrology Research Programme. Before and during FRMF design and construction, Monte Carlo calculations with MCNPX and PENELOPE codes were used to optimize the thickness of the shielding, the dimensions of the container, and the shape of detector collimators. Validation of the numerical models of the FRMF detectors and the results of the optimization are discussed in the paper.

Early-stage cervical carcinoma: The role of multidetector CT in correlation with histopathological findings

The objective of this retrospective study was to assess the diagnostic performance of multidetector CT (MDCT) in staging patients with surgical-pathological proven early-stage cervical carcinoma. A total of 22 women were referred for preoperative staging by MDCT, on a 16-row CT scanner. The protocol included scanning of the abdomen during the portal phase using a detector collimation of 16 × 0.75 mm and a pitch of 1.2. The evaluated parameters were: tumour detection, tumour maximal diameter, tumour extension to the uterine body and/or the vagina, parametrial invasion and presence of pelvic lymph node metastases. CT stage was assigned for each cervical carcinoma. The surgical–pathological stage was assigned on the basis of the operative findings and the histology report. The overall accuracy of MDCT in detecting and staging primary cervical carcinoma was 86% and 86%, respectively. Our results showed good diagnostic performance of MDCT in the detection and local staging of early-stage cervical carcinoma.

Role of 16-multidetector CT angiography in assessment of arterial and venous pulmonary anomalies in pediatrics

PurposeTo study the role of multidetector CT angiography in diagnosis, and follow up of venous and arterial pulmonary anomalies in pediatrics. Subjects and methodsRetrospective study was conducted upon 53 consecutive pediatric patients (24 F and 29 M, aged 4days to 5years; mean age 11.78months). CT examinations were done using 16-section CT scanner with a detector collimation of 16×0.75mm, pitch of 0.6, and gantry rotation time of 0.5s. Anatomic coverage extended from above the thoracic inlet to below the level of the L2 vertebra to include the origin of celiac trunk. Timed injection method was used. Post processing Image reconstruction was done in 3D volume rendering and maximum intensity projection (MIP). ResultsThe arterial pulmonary anomalies were more common than pulmonary venous anomalies, combined arterial and venous anomalies were seen in five cases and two cases had more than one type of pulmonary artery anomalies. The commonest pulmonary artery anomaly was atresia, followed by stenosis then hypoplasia. The commonest venous pulmonary anomaly was supracardiac total anomalous pulmonary venous return. ConclusionWe concluded that 16-MDCT is an accurate method for the diagnosis of congenital anomalies involving both pulmonary arteries and veins and also for preoperative planning and post operative evaluation.

A New Method Based on Position Sensitive Detectors to Measure Four-Degree-of-Freedom Geometric Errors of Linear Guide Rails

A novel method adopting position sensitive detector (PSD) and laser collimation technique to measure four-degree-of-freedom of linear guide rails is presented in this paper. The yaw and pitch errors can be obtained based on the relationship between output coordinates of horizontal PSD and angle of the mirror. Meanwhile, the horizontal and vertical straightness errors can be calculated by the relationship between output coordinates of vertical PSD and position of sampling points. Besides, BP neural network algorithm is used to correct the nonlinearity between actual and ideal output of PSD. The method is analysed theoretically in detail. The experimental results show that the four-degree-of-freedom of linear guide rails can be measured with high accuracy.

SU-E-CAMPUS-J-06: Development of a Tumor Blood Flow Measurement System for Proton Therapy Patients

Purpose: To develop a tumor blood flow rate measurement system utilizing positron emission after proton therapy for potential evaluation of the efficacy of radiotherapy, concurrent chemotherapy and/or antiangiogenesis therapy of proton therapy patients. Method: Daily proton treatment generates positron emission nuclei, i.e., 15O, 13N and 11C inside the treated volume of patients. In‐room measurement of activities of 15O as a function of time right after proton treatment can directly measure tumor blood flow rate due to the biological washout characteristics. A pair of NaI2 detectors and coincidence detection electronics were obtained. The NaI2 detectors were mounted on a modified C‐arm for good axial alignment and flexible isocentric rotation. The detector energy spectrum was calibrated using 60Co, 137Cs and 22Na sources. The energy window was set for 511 keV peaks. Current system is not optimized for collimation and shielding. The system performance was evaluated using 18F‐FDG. Proton irradiated water and/or ice were also measured for positron emission activity and the acquired data were analyzed. Detector shielding and collimation is under construction. IRB approval for proton patient blood flow rate measurement was obtained for evaluation of their tumor blood flow rates and changes over treatment course. Results: The C‐arm based detector platform demonstrated precise alignment and great flexibility for different treatment sites. The 18F‐FDG decay measurement using the system showed the measured half life is within 16s of the theoretical value. Activity measurement of proton irradiated water and ice showed about 10s half life difference between the measured and theoretical value. This was potentially due to the activation inside the water/ice container and lack of detector collimation and shielding. Conclusions: A non‐invasive in‐room tumor blood flow rate measurement system for proton therapy patients is under development. The preliminary data is reported. American Cancer Society Chris DiMarco Institutional Research Grant

Improved dose–volume histogram estimates for radiopharmaceutical therapy by optimizing quantitative SPECT reconstruction parameters

In radiopharmaceutical therapy, an understanding of the dose distribution in normal and target tissues is important for optimizing treatment. Three-dimensional (3D) dosimetry takes into account patient anatomy and the nonuniform uptake of radiopharmaceuticals in tissues. Dose–volume histograms (DVHs) provide a useful summary representation of the 3D dose distribution and have been widely used for external beam treatment planning. Reliable 3D dosimetry requires an accurate 3D radioactivity distribution as the input. However, activity distribution estimates from SPECT are corrupted by noise and partial volume effects (PVEs). In this work, we systematically investigated OS-EM based quantitative SPECT (QSPECT) image reconstruction in terms of its effect on DVHs estimates. A modified 3D NURBS-based Cardiac-Torso (NCAT) phantom that incorporated a non-uniform kidney model and clinically realistic organ activities and biokinetics was used. Projections were generated using a Monte Carlo (MC) simulation; noise effects were studied using 50 noise realizations with clinical count levels. Activity images were reconstructed using QSPECT with compensation for attenuation, scatter and collimator–detector response (CDR). Dose rate distributions were estimated by convolution of the activity image with a voxel S kernel. Cumulative DVHs were calculated from the phantom and QSPECT images and compared both qualitatively and quantitatively. We found that noise, PVEs, and ringing artifacts due to CDR compensation all degraded histogram estimates. Low-pass filtering and early termination of the iterative process were needed to reduce the effects of noise and ringing artifacts on DVHs, but resulted in increased degradations due to PVEs. Large objects with few features, such as the liver, had more accurate histogram estimates and required fewer iterations and more smoothing for optimal results. Smaller objects with fine details, such as the kidneys, required more iterations and less smoothing at early time points post-radiopharmaceutical administration but more smoothing and fewer iterations at later time points when the total organ activity was lower. The results of this study demonstrate the importance of using optimal reconstruction and regularization parameters. Optimal results were obtained with different parameters at each time point, but using a single set of parameters for all time points produced near-optimal dose–volume histograms.

New Hardware Solutions for Cardiac SPECT Imaging

Over the past decade, there has been intense interest in the modernization of scanners for cardiac SPECT imaging, with major changes in the design and functionality of hardware and software. This article aims at concisely reviewing recent developments in the field of detector materials, collimators, scanner configuration, and data acquisition strategies, as well as the new software reconstruction techniques typically associated with the new hardware. Since the new equipment and techniques can be employed either to reduce study acquisition time or to decrease radiation dose to the patient, the trade-off between these 2 desirable outcomes is also explored.