Characterisation of a high resolution small field of view portable gamma camera

A handheld, high-resolution small field of view (SFOV) pinhole gamma camera has been characterised using a new set of protocols adapted from standards previously developed for large field of view (LFOV) systems. Parameters investigated include intrinsic and extrinsic spatial resolution, spatial linearity, uniformity, sensitivity, count rate capability and energy resolution. Camera characteristics are compared to some clinical LFOV gamma cameras and also to other SFOV cameras in development.     

Investigation of an SFOV hybrid gamma camera for thyroid imaging

The Hybrid Compact Gamma Camera (HCGC) is a small field of view (SFOV) portable hybrid gamma-optical camera intended for small organ imaging at the patient bedside. In this study, a thyroid phantom was used to determine the suitability of the HCGC for clinical thyroid imaging through comparison with large field of view (LFOV) system performance.A direct comparison with LFOV contrast performance showed that the lower sensitivity of the HCGC had a detrimental effect on image quality. Despite this, the contrast of HCGC images exceeded those of the LFOV cameras for some image features particularly when a high-resolution pinhole collimator was used.A clinical simulation showed that thyroid morphology was visible in a 5 min integrated image acquisition with an expected dependency on the activity within the thyroid. The first clinical use of the HCGC for imaging thyroid uptake of ¹²³I is also presented.Measurements indicate that the HCGC has promising utility in thyroid imaging, particularly as its small size allows it to be brought into closer proximity with a patient. Future development of the energy response of the HCGC is expected to further improve image detectability.     

Intraoperative gamma cameras for radioguided surgery: Technical characteristics,performance parameters,and clinical applications

Several small gamma cameras (SGCs) intended for surgical use are now in development or currently being marketed. In this review, we discuss the characteristics, performance, and clinical use of SGCs which are hand-held and small enough to be easily managed by surgeons during their procedures. We expect that SGCs have the potential to be used more widely in radioguided surgery. As advancing molecular imaging technologies will broaden clinical indications, SGCs will likely be used and integrated with other imaging modalities into numerous types of radioguided surgery in the near future.     

CT dosimetry considerations in non typical conditions: The effect of scan field of view and table height selection

PurposeTo experimentally investigate the effect of the scan field of view (SFOV) selection and table height settings on the Computed Tomography Dose Index (CTDI) and the implications concerning patient effective and skin dose.MethodsAir-kerma length product (AKLP) measurements were carried out in a helical CT scanner using a pencil type dosimeter positioned in air and inside the holes of a head and a body phantom, using all available SFOV selections and different table height settings. Furthermore, using radiotherapy verification films placed on the CT table surface, the entrance surface air kerma (ESAK) profiles were derived with different SFOV and table height selections, both with and without a phantom on top of the films.ResultsThe AKLP is strongly dependent on the SFOV selection and the table height settings. Different SFOV selections correspond to the selection of different bowtie filters that shape the X-ray beam intensity, resulting in different ESAK values at the isocenter and at the other points within the scanning plane. With the off-center positioning the calculated CTDI values within the center and the periphery of the phantom change also, as a result of the different intensity and width of the X-ray beam to which are exposed to.ConclusionsThe existing protocols for calculating effective dose are limited to only two patient anatomy-SFOV combinations and cannot account for off-center positioning. Therefore, more work will be required to estimate the effective and skin dose for non-standard SFOV-patient anatomy combinations and off-center patient positioning.     

Principles of nuclear medicine imaging: planar, SPECT, PET, multi-modality, and autoradiography systems

The underlying principles of nuclear medicine imaging involve the use of unsealed sources of radioactivity in the form of radiopharmaceuticals. The ionizing radiations that accompany the decay of the administered radioactivity can be quantitatively detected, measured, and imaged in vivo with instruments such as gamma cameras. This paper reviews the design and operating principles, as well as the capabilities and limitations, of instruments used clinically and preclinically for in vivo radionuclide imaging. These include gamma cameras, single-photon emission computed tomography (SPECT) scanners, and positron emission tomography (PET) scanners. The technical basis of autoradiography is reviewed as well.     

99mTc thyroid imaging system using multiple imaging plates

A system for taking static thyroid ^99mTc images was devised by using multiple imaging plates (IPs) and a low-energy high resolution collimator. System spatial resolution of the IP systems and the gamma camera was determined by referring to standards set by the National Electrical Manufacturers Association. Sensitivity was represented by using lower detection limits (LDLs). The sensitivity and resolution of IP systems using 16 IP probes connecting two collimators and 9 IPs were determined by using a 20 ml thyroid phantom, and compared with the sensitivity of gamma cameras. The sensitivity of the IP systems increased in proportion to the number of IPs. The sensitivity and resolution of a probe using 6 IPs and a high resolution collimator were equivalent to or superior to the gamma camera for taking static thyroid ^99mTc images. IP systems can be applied clinically as mobile static nuclear imaging devices. The performance of IP systems should be thoroughly investigated for combinations of various collimators and the number of IPs in order to verify their efficacy for imaging all organs.     

Nouveautés en cardiologie nucléaire : une gamma caméra à semi-conducteurs dédiée à l’imagerie cardiaque

During the last few years, cardiac imaging made important breakthroughs thanks to the development of various techniques allowing the risk stratification of patients with coronary artery disease. The well-established single photon emission computed tomography (SPECT) as a myocardial imaging technique made an important progress with the recent improvement of high-speed volumic acquisition, using dedicated semi-conductor gamma camera. These cameras bring significant improvement to the image quality and the image acquisition time, which is now seven times lower. New type of artefacts is expected because of the geometry of detection, thus studies are still needed to assess the exact performance of this revolutionary technology.     

Traceable Calibration,Performance Metrics,and Uncertainty Estimates of Minirhizotron Digital Imagery for Fine-Root Measurements

Even though fine-root turnover is a highly studied topic, it is often poorly understood as a result of uncertainties inherent in its sampling, e.g., quantifying spatial and temporal variability. While many methods exist to quantify fine-root turnover, use of minirhizotrons has increased over the last two decades, making sensor errors another source of uncertainty. Currently, no standardized methodology exists to test and compare minirhizotron camera capability, imagery, and performance. This paper presents a reproducible, laboratory-based method by which minirhizotron cameras can be tested and validated in a traceable manner. The performance of camera characteristics was identified and test criteria were developed: we quantified the precision of camera location for successive images, estimated the trueness and precision of each camera''s ability to quantify root diameter and root color, and also assessed the influence of heat dissipation introduced by the minirhizotron cameras and electrical components. We report detailed and defensible metrology analyses that examine the performance of two commercially available minirhizotron cameras. These cameras performed differently with regard to the various test criteria and uncertainty analyses. We recommend a defensible metrology approach to quantify the performance of minirhizotron camera characteristics and determine sensor-related measurement uncertainties prior to field use. This approach is also extensible to other digital imagery technologies. In turn, these approaches facilitate a greater understanding of measurement uncertainties (signal-to-noise ratio) inherent in the camera performance and allow such uncertainties to be quantified and mitigated so that estimates of fine-root turnover can be more confidently quantified.     

Nouveaux traceurs TEMP : exemple des traceurs des protéoglycanes et de la mélanine

The majority of research program on new radiopharmaceutics turn to tracers used for positron emission tomography (PET). Only a few teams work on new non fluorine labeled tracers. However, the coming of SPECT/CT gamma cameras, the arrival of semi-conductors gamma cameras should boost the development of non-PET tracers. We exhibit in this article the experience acquired by our laboratory in the conception and design of two new non fluorine labelled compounds. The ^99mTc-NTP 15-5 which binds to proteoglycans could be used for the diagnosis and staging of osteoarthritis and chondrosarcoma. The iodobenzamides, specific to the melanin, are nowadays compared to ¹⁸F-fluorodeoxyglucose in a phase III clinical trial for the diagnosis and detection of melanoma metastasis. Our last development focus on BZA heteroaromatic analogues usable for melanoma treatment.     

Phantom evaluations of a dedicated dual-head scintimammography system

Results of aboratory evaluations are presented of the dual-head scintimammography system using two opposed and co-registered compact gamma heads. The system is intended for clinical studies imaging suspicious lesions in a compressed breast. The studies were performed using 5 cm and 6 cm compressed breast phantoms with lesion sizes from 6 to 10 mm and lesion to breast tissue activity ratios from 6 to 10. Two imagers with a field-of-view (FOV) of 15 cm×20 cm were placed on the opposite sides of the breast phartoms. In some studies anthropomorphic torso phantom was used to simulate realistic scatter gamma radiation field. Two types of parallel-hole lead collimators were employed. Combining the co-registered images from both detector heads resulted in an over two-fold increase in lesioin contrast in the central plane of the phantom and substantially increased detection sensitivity over the whole breast volume, especially of asymmetrically placed small lesions. The results confirm the important advantage of a co-registoed two-head scintimammography system over a single head system in lesion detection and localization.     

Lesion radioactivity concentration estimation using dual modality gamma ray/X-ray imaging

Although the use of dedicated gamma cameras in scintimammography permits closer access to the breast and improved spatial resolution relative to conventional gamma cameras, the task of quantifying the radiotracer concentration in the lesion relative to that in the surrounding breast tissue remains challenging because of the lesion-depth-dependent effects of attenuation and collimator blur. We are developing a dual modality scanner that combines digital x-ray mammography and a dedicated gamma camera on a common upright gantry. Here we present the results of a phantom study evaluating the use of the dual modality system for quantifying radioactivity in breast lesions. In addition to assessment of lesion activity, lesion volume estimates are necessary to quantify lesion radioactivity concentration. We have used multiple view x-ray imaging as a means of estimating lesion volume. Using phantom experiments, we have empirically derived a formula for correction of the measured z dimension of the lesion. The error obtained in quantification of lesion activity is approximately 10%. Lesion volume can be assessed with an accuracy comparable to that of lesion activity assessment using five x-ray views. These results suggest that the error in lesion concentration assessment is approximately 14%.     

Quality control for system count rate performance with scatter in gamma cameras

We aimed to analyze the optimal conditions to carry out the periodical statistical control tests of the gamma camera count rate performance. First we focused in reproducing the actual R₂₀ value of the gamma camera response. Second we studied the variability of this parameter in the statistical control test. We performed a reference measurement, which consisted of the determination of the complete curve relating observed and incident count rates, the counting model describing it and the reference R₂₀. This reference determined the conditions for the statistical control tests and the way to analyze the results obtained. Results from three different gamma cameras were studied. Each gamma camera showed a different behavior and required specific data analysis. The optimal conditions to perform the statistical control test were determined in each case. Our procedure provides the information necessary to correlate the average value of R₂₀ obtained in the quality control test with the reference one. The critical requirement to perform any statistical control test, that is to have a reduced variability of the control variable, can be fulfilled in this case only for relatively high activities.     

Predictive performance of random forest on the identification of mangrove species in arid environments

Machine learning methods are the most popular approaches for carrying out classification in remote sensing studies. Of the methods available, random forest (RF) is the one most often used due to its high predictive performance. The objective of this study was to assess the predictive performance of RF in identifying (classifying) mangrove species in an arid environment using two cameras: one conventional (visible part of the light, RGB), the other specialized (Green, Red, Near-infrared, GRN). The RGB and GRN bands were used with derived vegetation indexes (for each camera), the canopy height model (derived from photogrammetry), and distance to water (derived from raster analysis) to classify the study area in eight classes (including three mangrove species) using RF. Results suggest only slight differences in predictive performance (validation) between the products derived from the GRN and RGB cameras, the accuracy values ranged from 0.58 to 0.77 and from 0.53 to 0.72 for RGB and GRN, respectively. The most important variables were the distance to water and canopy height model for both cameras, followed by specific bands and vegetation indices. The study concludes that conventional cameras mounted in commercial drones can be used efficiently to identify mangrove species in arid environments when the classification model uses physical variables of the species (tree height) and the system (distance to water). Results of this study can be applied to describe spatial distributions by species in small or large patches of mangroves in arid environments, thus improving our ecological knowledge of this ecosystem.     

Coded aperture nuclear scintigraphy: a novel small animal imaging technique

We introduce and demonstrate the utility of coded aperture (CA) nuclear scintigraphy for imaging small animals. CA imaging uses multiple pinholes in a carefully designed mask pattern, mounted on a conventional gamma camera. System performance was assessed using point sources and phantoms, while several animal experiments were performed to test the usefulness of the imaging system in vivo, with commonly used radiopharmaceuticals. The sensitivity of the CA system for 99mTc was 4.2 x 10(3) cps/Bq (9400 cpm/microCi), compared to 4.4 x 10(4) cps/Bq (990 cpm/microCi) for a conventional collimator system. The system resolution was 1.7 mm, as compared to 4-6 mm for the conventional imaging system (using a high-sensitivity low-energy collimator). Animal imaging demonstrated artifact-free imaging with superior resolution and image quality compared to conventional collimator images in several mouse and rat models. We conclude that: (a) CA imaging is a useful nuclear imaging technique for small animal imaging. The advantage in signal-to-noise can be traded to achieve higher resolution, decreased dose or reduced imaging time. (b) CA imaging works best for images where activity is concentrated in small volumes; a low count outline may be better demonstrated using conventional collimator imaging. Thus, CA imaging should be viewed as a technique to complement rather than replace traditional nuclear imaging methods. (c) CA hardware and software can be readily adapted to existing gamma cameras, making their implementation a relatively inexpensive retrofit to most systems.     

Hot and cold contrasts in high-resolution Tc-99m planar scintigraphy: A survey of fifty-two camera heads using the PICKER thyroid phantom

This study was aimed at comparing the sensitivity and hot and cold contrasts obtained when imaging the PICKER thyroid phantom using gamma cameras fitted with either their ultra-high or high-resolution low-energy parallel hole collimator.Seventeen camera models from Elscint, General Electric, Siemens and Sopha Medical Vision were involved in the study for a total of 30 cameras and 52 camera heads. A single operator conducted the study in order to minimize the impact of human factors. The phantom contained about 74 MBq ^99mTc and was imaged at 10 cm from the collimator face with the energy window that are recommended by the camera manufacturer. A total of 1 million counts were accumulated.Hot and cold contrasts were in mean of about 0.05 higher when using an ultra-high-resolution than when using a high-resolution low-energy collimator. This higher contrast was obtained at the expense of a mean reduction in sensitivity of 30%. In particular, Elscint cameras demonstrated a 30% lower sensitivity whatever the collimator type. The Sopha Medical Vision DST and DSX cameras and the General Electric Magicam camera offered the lowest contrasts among the cameras with a high-resolution collimator. Although this was accompanied by a higher than the mean sensitivity for the DST and DSX, the Magicam demonstrated sensitivity roughly identical to the mean of all the cameras with a high-resolution collimator.     

Evaluation of Commercial Conjugates for Fluorescent Antibody Detection of Salmonellae

Fluorescent antibody (FA) reagents for Salmonella produced by Difco, Sylvana, and Clinical Sciences, Inc., were evaluated for physicochemical and performance characteristics. The Difco panvalent (A through 064) and the Difco polyvalent (A through S) were similar in physicochemical characteristics. They had less than 60% gamma globulin with 3% albumin and had fluorescein to protein (F/P) ratios of less than 10. The Sylvana conjugate had 81% gamma globulin with less than 1% albumin. Its F/P was 33.9. The Clinical Sciences reagent contained 75% unlabeled albumin as packaged in the Fluoro-kit. Analysis of the original conjugate showed 86.5% gamma globulin with only 0.5% albumin. The (F/P) was 32.8. The performance characteristics were determined by using a variety of Enterobacteriaceae and food and feed samples. All conjugates stained the homologous Salmonella strains. The majority of cross-reactions were limited primarily to the Arizona, Citrobacter, and Escherichia coli groups. The Difco panvalent was more reactive with heterologous organisms. It stained 89% of the Arizona compared with 42% stained by the Difco polyvalent (A through S) and 39% stained by the Sylvana and Clinical Sciences reagents. We found 90% agreement between FA and culture when the Difco polyvalent was used to examine food and feed samples and 94% agreement when the Clinical Sciences Fluoro-kit was used on another group of samples.     

Commissioning and performance testing of the first prototype of AlignRT InBore™ a Halcyon™ and Ethos™-dedicated surface guided radiation therapy platform

PurposeTo commission and assess the performance of AlignRT InBore™, a Halcyon™ and Ethos™-dedicated Surface Guided Radiation Therapy (SGRT) platform which combines ceiling-mounted cameras for patient setup and bore-mounted cameras for in-bore tracking.MethodsTo check the potential impact of InBore™ cameras on dose delivery, 16 SRS, H&N, breast and pelvis patients’ quality assurance (QA) treatment plans were measured with/without AlignRT InBore™ and using ArcCHECK® and SRS MapCHECK®. Impact on image quality was determined using Catphan® 540 phantom and considering all available MV and CBCT protocols (head, breast, chest and pelvis). The stability, accuracy and overall performance of AlignRT InBore™ was assessed using an MV Cube and anthropomorphic phantoms.ResultsComparison of 2D dose distributions with/without AlignRT InBore™ showed no impact on treatment delivery for all 16 QA checks (p-value > 0.25). 2D and CBCT images showed no artefacts or change in the contrast-to-noise ratio, resolution and noise values measured with Catphan® 540. Anti-collision sensors were unaffected by the bore-mounted cameras. Additionally, AlignRT InBore™ cameras allowed for motion detection with sub-0.5 mm accuracy and sub-0.4 mm stability with surface coverage of >50 × 60 × 35 cc. Accurate transition (sub-0.3 mm) from virtual to treatment isocentres was achieved. Finally, Halcyon™ rotations during CBCT and beam delivery resulted in limited camera vibrations with translation uncertainty <0.5 mm in left-right and anterior-posterior directions and <0.1 mm in head-feet direction.ConclusionAlignRT InBore™ provides SGRT setup and intrafraction monitoring capabilities with a performance comparable to standard SGRT solutions while having no adverse effect on Halcyon™.     

Les nouvelles gamma caméras en cardiologie nucléaire : D-Spect

Over the past few years, advances in nuclear medicine aimed at decreasing both the duration and dosimetry of exams, without decreasing image quality. In this setting, Spectrum Dynamics (D-Spect) is a new generation gamma camera dedicated to cardiac scintigraphy. Its technology includes solid-state detectors based on pixelated semiconductors, region-centric (cardiac area) scanning, high-sensitivity collimators and resolution recovery. An additional particularity is the patient position during scanning. Phantom studies showed an improvement of sensitivity compared to conventional cameras, at the price of a loss in geometric resolution, which is compensated by resolution recovery. Semiconductors detectors provide a better energy resolution than conventional detectors suited to double isotope acquisitions, and a high count rate allowing dynamic acquisitions. Only few clinical studies are available so far, they suggest performances similar to that of conventional cameras obtained with acquisitions duration reduced to few minutes. The next step is to establish a trade-off between acquisition duration and dosimetry reduction.     

Research note: Effect of bacillus cereus on performances of growing bulls

The effect of including Bacillus ceretis (BC) in a diet of growing bulls was examined. 64 German Holstein bulls (initial body weight: 187 kg) were allotted to one of two treatments (control and BC). The bulls were fed corn silage ad libitum and a restricted amount of concentrate (without BC or with 100 mg BC/kg). They were slaughtered with a final body weight averaging 555 kg. No significant treatment differences were detected for any feedlot performance or carcass characteristics measured. Bulls fed BC had a daily weight gain of 1472 g, control animals of 1425 g. Based on these findings, it may be concluded that under these conditions the inclusion of BC will not significantly improve performance of growing bulls.     

La caméra à semi-conducteur D-Spect : aspects techniques et applications cliniques

Clinical practice in nuclear medicine has largely changed in the last decade, particularly with the arrival of PET/CT and SPECT/CT. New semiconductor cameras could represent the next evolution in our nuclear medicine practice. Due to the resolution and sensitivity improvement, this technology authorizes fast speed acquisitions, high contrast and resolution images performed with low activity injection. The dedicated cardiology D-Spect camera (Spectrum Dynamics, Israel) is based on semiconductor technology and provides an original system for collimation and images reconstruction. We describe here our clinical experience in using the D-Spect with a preliminary study comparing D-DPECT and conventional gamma camera.