D. Townsend's research while affiliated with The University of Tennessee Medical Center at Knoxville and other places
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Publications (52)
Current systems for positron emission tomography (PET) generally cover a small solid angle which implies low sensitivity and therefore patient studies are relatively lengthy with acquisition comprising multiple bed positions. For cylindrical geometry, the axial field-of-view (FOV) may be increased by incorporating additional rings of block detector...
The solid angle of current cylindrical PET systems and hence the overall sensitivity can be increased by incorporating additional rings of block detectors. However, for a given scintillator volume of LSO, we may optimize the number of detectors and thus the number of rings of blocks in terms of point source and absolute sensitivity (NEMA NU-2 2001)...
Four generations of PET scanners have emerged since the first clinical PET system. In this paper we predict the achievable performance of a fifth generation PET scanner, defined as a fully 3D system with no septa, an axial FOV approaching 30 cm with a spatial resolution mainly dictated by the positron physics. The predictions are based on the HIREZ...
In positron emission tomography (PET), the concept of noise equivalent count rate (NEC) is a measure of image quality. It has been shown that the local signal-to-noise ratio in the images reflects the global signal-to-noise ratio, which, in turn, can be related to the NEC. Factors that affect the NEC include the scanner geometry and scintillator ma...
Since the ECAT 2, the first commercial positron emission tomograph developed by EG&G ORTEC, four generations of scanners can be identified. The first such scanners were based on sodium iodide (NaI(Tl)) scintillators, although as early as 1978 the transition to bismuth germanate (BGO) detectors had begun. By 1981, second-generation PET scanners with...
Application of the Fourier space deconvolution algorithm to three-dimensional (3D) reconstruction problems necessitates the computation of a frequency space filter; which requires taking the 3D Fourier transform of the system response function. In this paper, it is shown that for system response functions of the specific form d( theta , phi )/r2, w...
We have compared the performance of a PET scanner comprising two rotating arrays of detectors with that of the more conventional stationary-ring design. The same total number of detectors was used in each, and neither scanner had septa. For brain imaging, we find that the noise-equivalent count rate is greater for the rotating arrays by a factor of...
We report a patient who underwent surgical resection of two lung nodules that proved to be recurrent plasma cell granuloma, also known as inflammatory pseudotumor. Prior to surgery, positron emission tomography (PET) was performed with 18F-labeled fluoro-2-deoxy-D-glucose (18FDG) and rubidium-82 (82Rb). The 18FDG PET scan revealed that the nodules...
The distribution of specific radiolabeled biological compounds in tumor tissues can be imaged by positron emission tomography (PET). The substance used is fluorodeoxyglucose, labeled with the positron emitter fluorine-18. This substance is partly trapped in tumor cells with increased glucose metabolism. This noninvasive imaging technique allows to...
Different filters may be applied for accurate reconstruction of a three-dimensional (3-D) image from two-dimensional (2-D) parallel projections with the use of filtered backprojection. The set of such valid filters is characterized in Fourier space by a general filter equation. We demonstrate that all the solutions to this filter equation may be fo...
A positron emission tomography (PET) scanner with a reduced number of detectors per ring subtending two opposing arcs of 60 degrees and mounted on a circular support was developed. Projection data at all angles are acquired by rotating the detector assembly. The scanner has no septa, and data from the equivalent of 16 full rings of detectors are co...
A novel 3-D reconstruction algorithm for volume imaging in positron emission tomography (PET) is presented. This algorithm obviates the need to forward-project the data which have not been measured due to the finite length of the scanner. This results in a significant improvement in the reconstruction speed with respect to the algorithm of N.J. Pel...
A method of acquiring wide angle PET data has been described, the practical reasons for this development have been outlined. The ensuing problems associated with this have been addressed, and techniques are being developed to correct for them. The results generated from the preliminary studies suggest that the wide angle data acquisition is an acce...
The authors have assessed the response function both experimentally and theoretically for two commercial tomographs: CTI 931/08-12 and CTI 953B with and without interplane septa. Monte Carlo simulations were undertaken using the GEANT package from CERN. Spatial resolution (tomographic and axial) was calculated for line sources at various positions...
First Page of the Article
A PET camera consisting of two pairs of parallel area detectors has been installed at the cyclotron unit of VUB. The detectors are High Density Avalanche Chambers (HIDAC) wire-chambers with a stack of 4 or 6 lead gamma-electron converters, the sensitive area being 30 by 30 cm. The detectors are mounted on a commercial gantry allowing a 180 degree r...
We describe a detector based on the imaging of avalanches in gases initiated by ionization electrons produced by beta-particles entering an amplifying gap limited by two parallel electrodes. The avalanches are made visible by the addition of an efficient light-emitting vapour to noble gases such as argon or xenon. Imaging of the avalanches with an...
Conventional multislice positron cameras reconstruct a
three-dimensional distribution of a positron-emitting radioscope as a
set of two-dimensional transverse sections. Consequently, annihilation
photons which cross two or more planes are eliminated from the data.
Such an approach makes efficient use of the emitted photon flux. A
method is proposed...
An important feature of multi ring positron tomographs is the inter plane septa, the purpose of which is to reduce random and scattered coincidences. In general, such septa also eliminate the coincidence lines of response between pairs of detectors more than one ring apart. The operation of a camera without septa must result in an increase not only...
Production of useful Fluorine-18 quantities from the 18O(p,n)18F nuclear reaction is reported using a 590 MeV proton beam. The cross-section for this reaction is relatively low at these energies, and thus the fluorine yield is also low. In order to maximize the production yield, a target was constructed designed especially for the beam characterist...
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 pr...
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...
Positron Emission Tomography (PET) is a quantitative imaging modality that enables human physiology and metabolism to be measured in vivo for a number of important clinical applications (Phelps et al., 1986). The necessary measurements are obtained from the set of reconstructed tomographic images resulting from a PET scan. The important stages in t...
An important goal of positron emission tomography (PET) is the measurement of regional tissue concentrations of positron-emitting radionuclides. Such measurements are obtained from local count densities in PET images which have been corrected for background due to random coincidences and scattered photons. Photons which scatter and are undetected g...
Three dimensional medical images are usually obtained by stacking several parallel slices, each slice being reconstructed separately, using any classical 2 dimensional reconstruction algorithm. This method allows an efficient implementation of the reconstruction, and can be used whenever the measured projection data can be factorized into independe...
A prototype positron camera has been constructed consisting of two high density avalanche chamber (HIDAC) detectors operated in coincidence with a resolving time (2 tau) of 40 nsec. The detectors are multiwire chambers, with specially constructed lead converters added to improve the photon detection efficiency at 511 keV. The current HIDAC detector...
The sensitivity and specificity of single photon emission tomography with 57Co-labelled bleomycin (57Co-BLM) for the detection of cancer was determined from a prospective study involving a large group of patients selected to investigate roentgenographic abnormalities. Eighty-four of the 104 patients studied had malignant disease, of whom 76 had a p...
The role of positron emission tomography (PET) in medical research, particularly in neurology [1] and cardiology [2], is now well-established, whereas its application in routine clinical diagnosis is less obvious. In recent years, major technological achievements include the availability of both low-priced, compact medical cyclotrons and ring-type...
The sensitivity and specificity of scanning with 57Co-labelled bleomycin for the diagnosis of lung cancer were determined from a prospective study involving a large group of patients with an abnormal chest roentgenogram. A semi-quantitative analysis of the scintigram was obtained by defining an index in terms of the excess isotope uptake within the...
Patients displaying an abnormal chest X-ray, in some cases, cause a difficult diagnostic problem. A differential diagnosis between benign and malignant lesions is important to determine the choice of treatment i.e. whether or not to perform a thoracotomy. In a prospective study, we have examined the role of 57Co-bleomycin scanning for prethoracotom...
Patients displaying an abnormal chest X-ray, in some cases, cause a difficult diagnostic problem. A differential diagnosis between benign and malignant lesions is important to determine the choice of treatment i.e. whether or not to perform a thoracotomy. In a prospective study, we have examined the role of 57Co-bleomycin scanning for prethoracotom...
Only limited progress has been achieved in the treatment of ovarian cancer, the most common fatal gynaecological malignancy. Peritoneal dialysis with drugs known to be effective in ovarian cancer and large intraperitoneal fluid volumes (Belly Bath) have been used. The two critical determinants for a successful intraperitoneal chemotherapy programme...
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 activiti...
A high-density avalanche chamber (HIDAC) positron camera was used for tomographic imaging of the human thyroid in vivo. Images were made 7 and 24 h after the oral administration of the positron-emitting radionuclide, sodium iodide 124I (with activities varying between 0.3 and 1 mCi), to patients scheduled for either partial thyroidectomy or radioio...
Discusses two approaches towards improving the sensitivity and enlarging the useful field of view for a rotating positron camera by removing the constraint on phi . Weighted backprojection appears superior in that the camera response is more uniform and the images are less noisy than for the post-reconstruction scaling method. Fourier deconvolution...
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 vol...
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 ope...
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. U...
One approach to the three-dimensional, tomographic reconstruction of data from a planar dual-detector stationary positron camera necessitates frequency-space filtering of the image obtained from back-projection. It is therefore useful to have a closed-form expression for the appropriate filter, but the derivation is complicated by the fact that the...
A proportional chamber positron camera based on the principle of the high-density drift space has been constructed for medical imaging. Each of the two chambers has a 1 cm thick converter, 20 × 20 cm2 in size, with a photon detection efficiency of 8.5% at 0.5 MeV and a time resolution of 100 ns. With a new mode of operation, using neon gas, less th...
A major problem with the reconstruction of three-dimensional object distributions from focused tomographic images using Fourier transforms is the amplification of statistical noise in certain frequency components. This paper describes the use of a generalised matrix inversion technique to limit noise amplification to a level related to the spatial...
A positron camera consisting of two high density proportional chambers is described. It provides a spatial resolution of 2.4 mm FWHM, a maximum data rate of 3000 c.p.s. and a sensitivity of 25 c.p.s. per ¿Ci. Results of its application to angular correlation studies of condensed matter and to phantom and in vivo medical imaging are presented. A Fo...
Citations
... 20 Moreover, various publications reported using Monte Carlo simulations that using a LAFOV PET would boost the sensitivity. [21][22][23][24][25][26] Furthermore, some studies evaluated the spatial resolution and lesion detectability using Monte Carlo simulations. Schmall et al. used the EGS4 Monte Carlo code to investigate the depth of interaction (DOI) of 2 m AFOV PET using two and three layers of crystals and reported that the DOI information could enhance the spatial resolution from 5.7 to 5 mm. ...
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... In 1975, the CERN physicist David Townsend in collaboration with the University of Geneva and the Geneva Cantonal Hospital made important contributions to the reconstruction of PET images and to the development of 3D PET (4)(5)(6). ...
... It is also interesting to compare the phase unwrapping conditions of Theorem 9.2 with Orlov's condition that the continuous sampling orbit intersects any great circle on the unit sphere. Orlov's condition is the necessary and sufficient condition for the existence of a unique solution by the method of filtered back propagation (FBP) for 3D projection tomography under the Born approximation (thus no wrapped phases) [16]. Notably, among the three phase unwrapping schemes above, only scheme (ii) satisfies Orlov's condition. ...
... In 1975, the CERN physicist David Townsend in collaboration with the University of Geneva and the Geneva Cantonal Hospital made important contributions to the reconstruction of PET images and to the development of 3D PET (4)(5)(6). ...
... Positron emission tomography (PET) is a nuclear medical method which has been increasingly used in the assessment and definition of thoracic diseases using advanced computerized camera systems in combination with several radiopharmaceuticals [1]. The most commonly used radio-pharmaceutical is 18 F fluoro-2-deoxyglucose (FDG) in PET scanning. ...
... Les projections devront alors être filtrées au moyen du filtre dit de Colsher, similaire au filtre rampe 2D mais présentant en sus une dépendance vis-à-vis de la composante angulaire de la fréquence. Citons encore dans ce contexte les travaux de Stearns et al [SCH94] relatifs au filtrage associé à la rétro-projection filtrée 3D, ainsi que ceux de Defrise et al [DTC91] proposant un algorithme alternatif de rétro-projection filtrée, FAVOR, dans lequel le filtre de Colsher est remplacé par un autre filtre exact. ...
... Many detector modelling applications have been developed in the PET field including the pioneering work of Derenzo [184] who simulated arrays of detectors of different materials and sizes to study the effect of the inter-crystal septa and later on to optimize the optical coupling between BGO crystals and PMTs by taking into account the reflection and scattering along the detection system [185]. The search for an appropriate crystal for this imaging modality has been conducted in a comparative study of several crystals including BGO, CsF and NaI(Tl) [186], BaF 2 used in time-of-flight PET [187], liquid Xenon [188], LuYAP [189] and more recently GLuGAG and LFS-3 [190]. ...
... Over the last two decades there have been a number of attempts to harness multi-wire proportional chamber (MWPC) technology for use medical imaging, in particular, Positron Emission Tomography (PET). Among these, the HIDAC system [1] and the MUP-PET system [2] have been the most well-known. Within the Institute of Cancer Research/ Royal Marsden NHS Trust Hospital, the MUP-PET system has shown that clinically useful PET imaging can be achieved using this technology [3] . ...
... The consistency of the calculated values with measurements of u and D/μ in various other gas mixtures gives confidence in the method. [30], (rights) [31] study for two extremes, cold CO 2 and hot Ar [29]. Gases are denoted as cold, if ε stays close to the thermal energy (3/2)kT in the fields under consideration. ...
Reference: Gaseous Detectors
... The search for a novel technology able to detect and reconstruct events in scintillation detectors has become more and more important for dark matter and neutrino studies. An idea of detecting the light, optical and directional readout approach, proposed many years ago [10], has received renewed attention in recent years, where the challenges are the needs of high spatial resolution over large volumes, limited signal strength and non-negligible noise level [11]. The charge coupled devices (CCD) have been widely used in the past as high granularity light sensors and an upgrade of classical emulsion radiograph, such as GEM-based TPC with a 2-D CCD readout for directional dark matter experiments [12][13][14][15][16], thermal neutron imaging [17], single photon counting X-ray CCD camera spectrometer [7], photonic graph states [18], transparency measurement [19], a kilogram-scale Skipper CCD to detect coherent elastic neutrino nucleus scattering [20][21][22], and classical emulsion radiograph replaced by digital detector imaging especially in medicine applications [23]. ...
