Positron Camera Research Articles

Two detector MWPC positron camera with honeycomb lead converters: Performance and developments

Two detector MWPC positron camera with honeycomb lead converters: Performance and developments

A comparison of three 3-D reconstruction methods for large-area positron cameras

A comparison of three 3-D reconstruction methods for large-area positron cameras

Reconstruction tomography by nuclear scattering radiography.

The development of X-ray CT scanning has led to interest in other methods of reconstructive tomography. CT scanning is essentially an anatomic method. With the help of a positron camera, gallium 68 allows us to study the blood-brain barrier, ammonia 13 blood flow. This work is based upon the first experience of nuclear scattering radiography. Three main points will be demonstrated: (1) it is a research project, (2) the energy is provided by a cyclotron, (3) the particles are protons and are counted in three planes by scintillation detectors. They react with nuclei.

A Computer Assisted Ringdector Positron Camera System for Reconstruction Tomography of the Brain

A ring detector positron camera system for brain metabolism studies is being constructed at the Institute of Physics, University of Stockholm, in collaboration with the Departments of Neuroradiology and clinical Neurophysiology, Karolinska Sjukhuset, Stockholm, Sweden. The instrument utilizes 95 NaI(Tl) detectors and will simultaneously record coincidences from 1900 detector combinations. Each detector is coupled in coincidence with forty detectors on the opposite side of the ring. In the conventional stationary mode of operation the experimental system resolution is 10.5 mm. A new sampling technique has been developed to reduce the system resolution. Based on this technique, an experimental system resolution of 7 mm has been obtained.

A ring detector positron camera system: its merits: clinical experience.

A ring detector positron camera system for CT of the brain is described. The system uses 95 NaI (Tl) detectors, arranged with cylindrical geometry, for the simultaneous detection of coincidences from 1,900 detector combinations. With a new sampling technique an experimental system resolution of 7 mm FWHM has been obtained. The sensitivity was found to be 5,300 c/s with a 100-keV energy threshold and using a 19.2-cm-diameter cylindrical phantom with a homogeneous specific activity of 1 muCi/cm3. A clinical study of blood-brain barrier damage using 68Ga-EDTA is reported.

Quantitative measurements of cerebral metabolism with the searle positron camera

Quantitative measurements of cerebral metabolism with the searle positron camera

Medical imaging with a high resolution proportional chamber positron camera

Medical imaging with a high resolution proportional chamber positron camera

Inhalation imaging with oxygen-15 labeled carbon dioxide for detection and quantitation of left-to-right shunts.

Quantitation of left-to-right shunts was determined noninvasively from the pulmonary clearance pattern of inhaled 15oxygen-labeled carbon dioxide (C15O2). After a single breath inhalation of C15O2, counts over the lungs were obtained from sequential 0.5 sec positron camera images. In 21 patients without left-to-right shunts, counts declined exponentially due to the washout of C15O2 by the pulmonary blood flow. In 22 patients with left-to-right shunts, this monoexponential pulmonary clearance pattern was interrupted by an abnormal upward deviation, indicating tracer recirculation through the shunt to the lungs. Following surgical shung closure in 10 patients, pulmonary C15O2 clearance patterns became normal in nine and showed a small residual left-to-right shunt in one. Shunt size was derived from the ratio of the height of the recirculation curve to the height of the initial inhalation peak. These values significantly correlated with shunt size as determined by oximetry (r = 0.83).

Localization of 113mIn- and 67Ga-Labeled Poly-methylene-Phosphonates in Myocardial Infarct

SummaryWe have investigated the usefulness of two new 67Ga-chelates, i. e. 67Ga-ethylene diamine tetramethylenephosphonate (67Ga-EDTMP) and 67Ga-diethylenetriamine pentamethylene phosphonate (67Ga-DTPMP), and of two 113mIn-chelates, i. e. 113mIn-EDTMP and 113mIn-DTPMP, for imaging myocardial infarct in rabbits. The agents were prepared by adding 113mIn3+ or 67GaCl4 – ion to 20–50 mg of EDTMP or DTPMP stock solution and neutralizing to pH of 7.4. Myocardial infarcts were introduced into 15 rabbits by ligation of the left anterior descending coronary artery. The rabbits were then injected with a mixture of 113mIn-EDTMP, 45Ca-EDTMP or 67Ga-EDTMP and corresponding DTPMP chelates. The radioactivity-mapping of the heart was made by removing the outer and inner layers of pale or hemorrhagic infarct. Beta and gamma radioactivity in the heart and other tissue samples were obtained. There was excellent correlation between the radioactivity distribution of the 45Ca- and 113mIn-chelates. The predominant concentration was in the bones, bladder, kidney and infarcted myocardium. For 113mIn-EDTMP, an average ratio of 30 :1 between infarcted and normal myocardium (IM/NM) was obtained at 24 hrs after ligation. This ratio peaked 48 hrs after ligation to 50:1. For 6 7Ga-EDTMP this ratio varied from (7–10): 1. The blood clearance 67Ga-EDTMP was slow. Gel filtration of serum containing 113mIn-EDTMP and 67Ga-EDTMP showed that 45% and 86% of the radioactivity were protein bound. We observed that protein binding of metal chelates is an important characteristic for localization in myocardial infarct. The two pairs of 113mIn-EDTMP and 201T1+ ion or 67Ga-EDTMP and 13NH4+ ion should be useful for multiple imaging of myocardial infarct with the gamma or positron camera, respectively.

Three-dimensional imaging in the positron camera using Fourier techniques

A mathematical algorithm for three-dimensional reconstructions in the positron camera is described. Fourier techniques have been adapted for use in analysing the data from cameras with limited detector configuration. Noise instabilities from random fluctuations in the data are discussed and treated. The technique is tested on a computer-generated phantom and the results are presented. Ways of incorporating the effects of Compton scattering and detector response into the algorithm are discussed. It is concluded that the method is feasible and practical for obtaining accurate reconstructions.

Experimental tests of proton beam localization.

The depth of penetration of heavy charged-particle therapy beams is sensitive to the density of tissues traversed. Maximum depth of dose contours will vary appreciably as the beam passes through bone, muscle, lung, and air or gas. Calculations suggest that beam activation of the short-lived positron-emitting isotope 15O in vivo will permit localization of proton therapy beams with resonable detected-event density and dose. Preliminary tests of this method indicate that the beam can be located at depth with a typical dose of 15 rad, using a large field-of-view positron camera on-ling. This technique is also applicable to other heavy charged-particle beams, negative pions, and heavy ions.

Three-Dimensional Radionuclide Tomography With Circular Ring Positron Camera

Transverse axial positron annihilation coincidence detection tomography with circular ring transaxial positron camera (CRTAPC) will be described. Some of the merits and charac-teristics of the circular ring geometry in comparison to others will be discussed, and performances of the CRTAPC will be presented.

Performance and Evaluation of the Circular Ring Transverse Axial Positron Camera (CRTAPC)

Transverse axial positron annihilation coincidence detection tomography with a stationary circular ring posi tron camera system is described. A prototype constructed with 64 NaI(T1) crystal system has the capability of recording 736 - 1312 simultaneous coincidence pairs and is able to perform certain dynamic function studies.

Technology Update on Fast Plastic Scintillators for Medical Applications

Plastic scintillators appear to have potential utility in three research areas related to nuclear medicine: (1) high count rate applications in general, (2) positron camera applications, and (3) positron source localization through measurement of relative arrival times of annihilation quanta at two co-linear detectors. These three areas of applicability depend on improvement in three specific areas of plastic scintillator technology: (a) development of plastics with very fast decay times, (b) development of plastics with greatly improved high energy photon detection efficiencies (high-Z loaded plastics), and (c) improvement of fast timing system capabilities. The three preceding areas of improvement are discussed.

A Gas-Filled Channel Converter for Fast Coincidence Cameras

The construction of a mosaic of very small proportional counters consisting of high-atomic-number cathodes with conventional thin axial wire anodes was previously proposed1 for improvement of the time resolution and data rate of multiwire positron cameras and similar devices which are useful in medical diagnosis. In this paper, we show that the physical construction and electrical connections of the mosaic described are simpler than anticipated, and that manufacturing prospects compare favorably with those for multiwire chambers. The performance data of prototypes will be reported in a forthcoming issue of this journal.

Efficiency optimization analysis for dynamic function studies with 3-D transaxial positron cameras

Efficiency optimization problems for circular ring transverse axial positron camera systems (CRTAPC) have been investigated. The analyses include source activity, camera dimension, collimator and phantom sizes. The results indicate possibilities for fast dynamic function studies in the time region of a few seconds for reasonably small phantom sizes having a uniform activity distribution.

High Efficiency Collimator-Converters for Neutral Particle Imaging with MWPC

A MWPC with external collimator converter system has been developed specifically for the detection of 0.511 MeV gammas in a positron camera. The design basis is applicable also to the imaging of other gammas and neutrons. The converter consists of honeycomb cells which provide an enhanced area of escape surface as well as restricting the range of conversion electrons to the cell dimensions. (WHK)

Axial Tomography and Three Dimensional Image Reconstruction

A number of existing cameras for Nuclear Medicine imaging of radio-isotope distributions give depth information about the distribution. These devices have in common that they provide tomographic images of the object, that is, that images of a given object plane have that plane in focus and all other object planes contribute an out-of-focus background superimposed on the in-focus image. We present here a method for three dimensional reconstruction of these axial tomographic images which removes the blurred off-plane activity from a number of transverse planes simultaneously. The method is applicable to a number of tomographic cameras, such as the multiple single-pinhole camera, the rotating slanted-hole collimator, the Anger focussing tomographic scanner, and the positron camera. The method can be implemented on a small computer having a disc system.

Circular Ring Transverse Axial Positron Camera for 3-Dimensional Reconstruction of Radionuclides Distribution

The transverse axial 3-dimensional image reconstruction concepts developed in transmission tomography brought the nuclear medicine and diagnostic radiology into the realm of quantitative analysis of the 3-dimensional image hitherto superimposed in two dimensions. Two factors make it appropriate to design a positron camera system at this time, (1) analogy between the emission of photons following a positron annihilation and the transmission of photons, and (2) the already demonstrated success of positron camera multidetector systems. The camera consists of one layer of 64 (or 72) NaI(T1) crystals and PM tubes that simultaneously record coincidences from 2 × 736 (or 2 × 1116) detector combinations in a circular array.

A Positron Camera by Use of a Focal Detector of Hexagonal Multi-Crystal Array

高計数率に耐え得る多結晶型焦点検出器を作成し, 市販のガンマ・カメラと組み合わせてポジトロン・カメラを作成した。高速電子回路を用いた同時計数回路を用いて陽電子消滅に伴う対γ線を検出し, 位置計算をする。同時計数しない無効のγ線ががンマ・カメラに入射するのを粗い焦点型コリメータを用いて低減し, 最高計数率の改善を図るとともに, 検出効率の一様性の改善を図った。性能の概要は, (1) 最高計数率: 約2.5～4kcps, (2) 検出効率: 0.6～0.9dots/sec/μCi, (3) 位置分解能: 6～9mm (FWHM) , ( (1) ～ (3) の値はコリメー表面から線源までの距離に依存する。) , (4) 有効視野: 直径20cmの円形領域 (深さ20cmの面) である。