High-density Avalanche Chambers Research Articles

The Bristol HIDAC 2D-ACAR Spectrometer

We describe the Bristol spectrometer for positron annihilation Fermi surface studies utilising high-density avalanche chambers (HIDACs) as position sensitive detectors. Measurements on α-SiO2 show, through the momentum distribution of para-positronium, the substantial improvement in resolution compared to Anger cameras. Measurements of the Fermi surface of V are used to determine the resolution. The new spectrometer is found to have an efficiency of 12.5 ± 0.6 % and a (coincidence) contribution to the position resolution of 0.96 ± 0.1 mm.

Combining variational and model-based techniques to register PET and MR images in hand osteoarthritis

Co-registration of clinical images acquired using different imaging modalities and equipment is finding increasing use in patient studies. Here we present a method for registering high-resolution positron emission tomography (PET) data of the hand acquired using high-density avalanche chambers with magnetic resonance (MR) images of the finger obtained using a ‘microscopy coil’. This allows the identification of the anatomical location of the PET radiotracer and thereby locates areas of active bone metabolism/‘turnover’. Image fusion involving data acquired from the hand is demanding because rigid-body transformations cannot be employed to accurately register the images. The non-rigid registration technique that has been implemented in this study uses a variational approach to maximize the mutual information between images acquired using these different imaging modalities. A piecewise model of the fingers is employed to ensure that the methodology is robust and that it generates an accurate registration. Evaluation of the accuracy of the technique is tested using both synthetic data and PET and MR images acquired from patients with osteoarthritis. The method outperforms some established non-rigid registration techniques and results in a mean registration error that is less than approximately 1.5 mm in the vicinity of the finger joints.

Performance characteristics of a small animal PET camera for molecular imaging

The performance of a novel type of animal PET camera, the quad High-Density Avalanche Chamber (HIDAC) was assessed for a non-rotating 16-module system. Spatial resolution was 1.0 mm, and invariant within a standard deviation ⩽5%. Absolute sensitivity was 0.95%, and the scatter-background corrected sensitivity was 0.75%. The count rate capability was linear at typical activities used in animal imaging, with a 20% loss at 11.5 MBq. The camera demonstrates small regions of radiotracer uptake with excellent detail in the mouse.

The effect of β + energy on performance of a small animal PET camera

The effective spatial resolution of a positron emission tomography (PET) scanner is determined in part by the initial energy of the positron, which is a function of the radionuclide. For F-18 ( E max=0.633 MeV) the mean positron range in water is small (0.6 mm). However, many other useful positron-emitting nuclides have higher energies, for example Ga-68 ( E max=1.899 MeV, mean range 2.9 mm) has one of the highest. The performance of a non-rotating, 16 module high density avalanche chamber (quad-HIDAC) small animal PET scanner was measured using both F-18 and Ga-68 to represent the extremes of high and low positron energy. The count rate performance—scatter fraction and noise-equivalent count rate (NEC)—were measured for both isotopes. Data were also collected for a spatial resolution phantom with rectangular arrays of holes of diameter 2.0, 1.5, 1.0 and 0.5 mm with the centres separated by 4.0, 3.0, 2.0 and 1.0 mm respectively. The NEC, measured for both 70 and 200 cm 3 cylindrical phantoms, was approximately linear up to 30 MBq, but shows a rapid drop-off above this value. The spatial resolution phantom showed that 1 mm objects are just resolved with F-18, but none of the targets are resolved for Ga-68. In conclusion, spatial resolution is dominated by the choice of isotope down to 1 mm, with sensitivity and count-rate data being largely independent of positron range.

From 3-D positron emission tomography to 3-D positron emission tomography/computed tomography: what did we learn?

The recent introduction of combined positron emission tomography (PET)/computed tomography (CT) scanners is having a far-reaching effect on the field of medical imaging by bringing functional imaging to the forefront in radiology, oncology and other specialties. The PET/CT scanner is an evolution in technology combining two well-developed imaging modalities: anatomical imaging with CT and functional imaging with PET. The first prototype PET/CT scanner was a consequence of a succession of steps that, in chronological order, included the development of the High Density Avalanche Chamber (HIDAC) PET camera, 3-D PET methodology and the rotating partial-ring tomograph (PRT). The successful completion of each step was a prerequisite to progress to the next phase, and the lessons learned could then be applied to subsequent initiatives. This review will map the milestones from 3-D PET to 3-D PET/CT and assess the role each step played in the development of PET instrumentation over the past two decades.

Performance evaluation of the 16-module quad-HIDAC small animal PET camera

The quad-HIDAC small animal PET camera is a quadratic array of high-density avalanche chambers; the camera described in this publication consists of 16 modules. We present the system response using point and line sources and a mouse phantom. The quad-HIDAC camera exhibits a count rate stability of better than 1% and linearity of response to coincidences up to 2.2 × 105 cps at 16 MBq activity. Corrected for deadtime and random coincidences, the efficiency for the line source is 0.011, of which unscattered coincidences yield 0.009. The scatter fraction originating from the detectors is 0.22. Absorption within the mouse phantom was 20% and the scatter fraction increased to 0.29. Resolution is uniform within the entire field-of-view, which is 28 cm axially and 17 cm radially. Reconstruction of a point source yields a resolution of 1.1 mm FWHM for all three components. The performance of the camera demonstrates its excellent suitability for the functional imaging of small animals.

Feasibility of imaging photodynamic injury to tumours by high-resolution positron emission tomography.

One early effect of the treatment of tumours by the new modality photodynamic therapy (PDT) is a reduction in tumour glucose levels. We have employed the widely used positron-emitting glucose analogue flurorine-18 fluoro-2-deoxy-D-glucose ([18F]-FDG), to determine whether, in principle, PDT-induced injury might be delineated non-invasively and quantitatively by positron emission tomography (PET). The scanner was of the high-density avalanche-chamber (HIDAC) type with a resolution of 2.6 mm. Subcutaneous T50/80 mouse mammary tumours, sensitised by haematoporphyrin ester, were illuminated by graded doses of interstitial 630 nm light. Thirty hours later, any remaining viable tumour was detected (a) by region-of-interest analysis of the PET images and (b) by gamma counting the excised tumour. PET measurements of % uptake of [18F]-FDG into tumour correlated closely with ex vivo gamma counting (slope=0.976, r2=0. 995), validating the in situ method. Uptake into untreated, control tumours was 3.8%+/-1.1% of the injected activity. Uptake of [18F]-FDG into treated tumours decreased by 0.7% for every 100 mm3 reduction in remaining viable histological volume. Outcome was further compared with that measured by (a) T2-weighted proton imaging on a 4.7-T magnetic resonance imaging (MRI) system and (b) histological analysis of subsequently sectioned tumours. PET using [18F]-FDG described the absolute volume of surviving tumour histological mass to the same degree as high-resolution MRI. The conclusion of these initial studies is that PET with [18F]-FDG, although non-specific, quantitatively described at early times the extent of tumour destruction by PDT.

32. Assessment of a high-density avalanche chamber (HIDAC) PET camera for imaging head and neck tumours with 18FDG in humans

Hastings, D. L.1; Jeavons, A. P.4; Waller, M. L.1; Collins, C. D.2; Chandler, R. A.4; Dettmar, C. A.R.4; Hand, J. C.1; Johnson, R. J.2; Slevin, N. J.3 Author Information

High-density avalanche chambers for positron emission tomography

A positron tomograph for radiopharmaceutical and medical research is under construction. In its final stage it will cover six high-density avalanche chambers (HIDAC) in a hexagonal arrangement. Each detector with a sensitive area of 50 × 28 cm 2 will consist of a stack of four pairs of multihole photon-to-electron converters with a multiwire proportional counter (MWPC) in between. An experimental investigation of detector properties as time and spatial resolutions as well as detector efficiency in dependence to converter structure, electric field strength and counting gas mixture preceded the final design of these detectors. Results of these studies are outlined. Furthermore, longitudinal tomograms taken with a stationary test camera are presented.

PET with the HIDAC camera?

In 1982 the first prototype high density avalanche chamber (HIDAC) positron camera became operational in the Division of Nuclear Medicine of Geneva University Hospital. The camera consisted of dual 20 cm × 20 cm HIDAC detectors mounted on a rotating gantry. In 1984, these detectors were replaced by 30 cm × 30 cm detectors with improved performance and reliability. Since then, the larger detectors have undergone clinical evaluation. This article discusses certain aspects of the evaluation program and the conclusions that can be drawn from the results. The potential of the HIDAC camera for quantitative positron emission tomography (PET) is critically examined, and its performance compared with a state-of-the-art, commercial ring camera. Guidelines for the design of a future HIDAC camera are suggested.

Clinical applications with the HIDAC positron camera

A high density avalanche chamber (HIDAC) positron camera has been used for positron emission tomographic (PET) imaging in three different human studies, including patients presenting with: (I) thyroid diseases (124 cases); (II) clinically suspected malignant tumours of the pharynx or larynx (ENT) region (23 cases); and (III) clinically suspected primary malignant and metastatic tumours of the liver (9 cases, 19 PET scans). The positron emitting radiopharmaceuticals used for the three studies were Na 124I (4.2 d half-life) for the thyroid, 55Co-bleomycin (17.5 h half-life) for the ENT-region and 68Ga-colloid (68 min half-life) for the liver. Tomographic imaging was performed: (I) 24 h after oral Na 124I administration to the thyroid patients, (II) 18 h after intraveneous administration of 55Co-bleomycin to the ENT patients and (III) 20 min following the intraveneous injection of 68Ga-colloid to the liver tumour patients. Three different imaging protocols were used with the HIDAC positron camera to perform appropriate tomographic imaging in each patient study. Promising results were obtained in all three studies, particularly in tomographic thyroid imaging, where a significant clinical contribution is made possible for diagnosis and therapy planning by the PET technique. In the other two PET studies encouraging results were obtained for the detection and precise localisation of malignant tumour disease including an estimate of the functional liver volume based on the reticulo-endothelial-system (RES) of the liver, obtained in vivo, and the three-dimensional display of liver PET data using shaded graphics techniques. The clinical significance of the overall results obtained in both the ENT and the liver PET study, however, is still uncertain and the respective role of PET as a new imaging modality in these applications is not yet clearly established. To appreciate the clinical impact made by PET in liver and ENT malignant tumour staging needs further investigation, and more detailed data on a larger number of clinical and experimental PET scans will be necessary for definitive evaluation. Nevertheless, the HIDAC positron camera may be used for clinical PET imaging in well-defined patient cases, particularly in situations where both high spatial resolution is desired in the reconstructed image of the examined pathological condition and at the same time “static” PET imaging may be adequate, as is the case in thyroid-, ENT- and liver tomographic imaging using the HIDAC positron camera.

Positron camera with high‐density avalanche chambers

AbstractThe results of an extensive investigation of the properties of high‐density avalanche chambers (HIDAC) are presented. This study has been performed in order to optimize the layout of HIDAC dectetors, since they are intended to be applied as position sensitive detectors for annihilation radiation in a positron emission tomograph being under construction.

Tomographic imaging of the human thyroid with a positron camera before and after partial thyroidectomy.

A high-density avalanche chamber positron camera was used for tomographic imaging of the human thyroid before and after partial thyroidectomy. Images were made between 6 and 24 h after oral administration of the positron-emitting radionuclide, Na-124I with activities varying between 0.1 and 0.3 mCi before the surgical intervention and with activities between 0.03 and 0.05 mCi following partial thyroidectomy. The results of thyroid imaging performed on 50 patients and their surgical relevance are discussed; as an illustration, one typical case is presented. As a consequence of the high spatial resolution of the camera (2.5 mm full width at half maximum), the functional volume of the thyroid may be estimated from the transaxial tomographic sections before and following partial thyroidectomy, correct to about 10%. The thyroid surface, defined by the contours from each transaxial section, may be displayed using three-dimensional shaded-graphics techniques. This new imaging technique makes possible a fully three-dimensional description of the thyroid in vivo and contributes significantly to the surgical follow-up.

Volume measurement in vivo using positron tomography

The high density avalanche chamber (HIDAC) positron camera has been used for tomographic imaging of the human thyroid in vivo. Images are made seven and twenty-four hours after oral administration to the patient of the positron-emitting radionuclide124I. As a consequence of the high spatial resolution of the camera (2.5 mm fwhm), the functional volume of the thyroid may be estimated from the tomographic images to within about 12%. This paper discusses some of the studies performed to ensure reconstructed images free from artifacts and distortions, and, as illustration of the technique, two typical patient cases are presented.

The High-Density Avalanche Chamber for Positron Emission Tomography

The development of wire chambers for positron emission tomography continues at CERN. In its present form, the basic detector is called a HIgh Density Avalanche Chamber (HIDAC). Owing to the Penning effect, electron avalanche multiplication is obtained in the gamma-ray converter: coincidence time resolution is reduced to 20 ns and stable chamber operation is achieved with a safe, non-polymerizing gas mixture. Spatial resolution remains at 2-3 mm FWHM. A rotating camera consisting of two 20 × 20 cm chambers has now been under evaluation at Geneva Hospital for one year. Multilayer printed-circuit techniques are now used to construct chambers with multiple converters, thus raising detection efficiency from 7.5 to 20%. Read-out electronics and back-projecting memory are being developed to handle the high data rate from these chambers. A four-chamber positron camera designed to achieve 100,000 coincidences s-1 is nearing completion.

Image Reconstruction for a Rotating Positron Tomograph

A high-resolution positron tomograph consisting of two high-density avalanche chambers mounted on a rotating gantry has been installed in the Nuclear Medicine Department of the Cantonal Hospital in Geneva. Positron annihilation data are collected from six detector positions and back-projected in real time to form a single three-dimensional image. Up to 16 transverse or longitudinal sections may be imaged simultaneously. The derivation of the appropriate deconvolution filter is described in this paper, and the first images taken in the transverse mode are presented. It is shown that quantitative information can be obtained from such images.

A note on the interaction between surface waves and wind profiles : Miles John W., 1965. J. Fluid Mech., 22 (4): 823–827.

High resolution is a common demand of many imaging technologies currently used for small animals. Computed tomography, magnetic resonance imaging, and ultrasound imaging are highly developed imaging techniques providing submillimeter spatial resolutions. Along with single-photon emission computed tomography, positron emission tomography (PET) is the most sensitive molecular imaging modality for in vivo imaging. This chapter introduces the basics of high-resolution small animal PET with a strong focus on multiwire proportional chamber PET. The four-detector high-density avalanche chamber PET will be highlighted as a high-resolution PET system for small animals and applications will be given in cardiology, oncology, and neurology.