[en] About two third of the papers presented at this 6th Colloquium on 'Information Processing in Medical Imaging' belong to Nuclear Medicine, in 8 scientific sessions out of 9. Nuclear magnetic resonance and nuclear scattering imaging, nuclear medicine imaging, positron and gamma emission tomography. Compton scattering tomography, dynamic function studies, and systems are included

[en] Nuclear Magnetic Resonance (NMR) presents an exciting potential for medical diagnosis. The short exposure times to both magnetic fields and radio-frequency waves indicates its non-hazardous nature. Since NMR information is most likely to overlap the data provided by x-ray computerized tomography, and in size and cost the equipment is likely to be similar, it is worthwhile to avoid as much as possible the pitfalls of CT in designing NMR imagers. Of these the most obvious is the desire to avoid reconstruction techniques where the data at any one region in the image is dependent on (and affects) the data in all other regions of the image, since in this case artifacts can arise that result in images with false or uninterpretable information. Also, in the interest of time, it is desirable to accumulate simultaneous data from as many elements in the image as possible. These requirements are not necessarily compatible, and system design requires prioritizing them. We present the imaging properties of a NMR imager that utilizes a Varian Magnet with 30 cm diameter pole tips and a 10 cm gap, operated at 3.52 KGauss (15 MHz hydrogen resonant frequency). Line readout techniques are used to avoid the need for reconstructions. An analysis is also presented of the potential for imaging other atomic components of the human body. When comparing to hydrogen it is assumed that the magnetic field strength can be increased so that the imaging can be performed at the highest possible frequency consistent with obtaining acceptable RF penetration. The clinical utility of images of these other elements will be strongly dependent on the performance of the system for hydrogen

[en] An investigation into the use of principal components analysis in dynamic studies is described. The parameters obtained for three organs -kidneys, liver and thyroid- are compared in each case with those obtained from a standard physiological model. It is shown that the principal component parameters give better class separation than the physiological model parameters for renal and thyroid dynamic studies but with limited usefulness in the latter case. The physiological model provides better class separation for liver dynamic studies. For renal studies some measure of the degree of function can be implied from the principal components parameters

[en] A microprocessor-based device has been developed to virtually eliminate the effects of nonlinearity and nonuniformity in radioisotope camera signals. Imperfections in the X and Y spatial signals or the Z energy signal can otherwise lead to spatial distortion, non-constant sensitivity, and flood non-uniformity in the resulting images. A device operates in real time on each event from the camera, and is fast enough to allow counting rates up to 120,000 per second without loss. Non-linearities in the X and Y signals are eliminated by carrying out an on-the-fly translation to corrected U and V position coordinates. The translation table is constructed based on calibration images of a parallel line phantom. Possible variations in the Z signal are accomodated by also including in the table a 64 x 64 array of spatially-depedent energy windows. These data are automatically generated based on a calibration flood image. The device operates in conjunction with an MDS Modumed Data System, and has been demonstrated using three different radioisotopes cameras. In all cases, significant improvement in image linearity and uniformity has been observed

[en] A new circular ring positron ECT system has been proposed, in which the detectors are mounted on a circular gantry with 'unequal-spacings' so as to provide the fine and uniform linear sampling during 360⁰ rotation of the gantry around its center. This paper presents an iterative method for searching the optimal detector arrangement, and clarifies sampling characteristics of the obtained arrangements with various parameters such as the number of detector, angular margin in arrangement, and some other parameters in the iterative method. It is concluded that, if the total angular margin is not smaller than the angle subtended by one detector unit, we can determine a detector arrangement having a satisfactory sampling characteristics suitable for the reconstruction tomography

[en] Causes of the non-uniformity response to a flood source and their respective importance have been studied on an image intensifier camera. To improve this response, corrections on the spatial variations of energy response and the spatial distortions due to the coordinate computation principle for this camera have been performed. These corrections are made off line, by using a data processing system, on the list mode acquisition of spatial coordinates (X,Y) and energy information (W). They have improved the uniformity index from 35% to 7% on an acquisition that was made with a 20% spectrometric window. Clinical image quality has also been improved, as these corrections allows the use of a narrower spectrometric window (20% or less)

[en] Temporal Fourier analysis on a time series on images concentrates on the change in information contained in each picture element as a function of time. A TFT limited to the first Fourier coefficients, will yield two functional images, the amplitude and the phase, respectively. In the case of periodic phenomena such as the beating of the heart or the breathing of the lungs amplitude and phase are the most characteristic parameters available for functional imaging. In gated cardiac blood pool studies, count rate derived functional images allow a great accuracy in the detection and localisation of asynergy. Any transient function f(x) wich is not periodic but defined within an internal (-T,T) can be made periodically by defining f(t + 2T) = f(t). TFT can then be applied to study such phenomena as first pass blood flow. The amplitude image corresponds to the changes in counts within the image series, the phase images to the time of transit. The two functional images will permit a rapid and sensitive assessment of the vascularisation of various structures or lesions. As a rule, the information content in a dynamic series of images is used with maximal efficiency. This highly increases the resolution in time and space of studies limited by poor count rate statistics as compared with other functional imaging techniques

[en] The scientific validity of a method requires in final analysis that the results are independent of the user. This statement which would in other circumstances appear tautological is actually controversial in nuclear medicine, where the skill of the operator tends to be valued. But if the operator is interested in the outcome of the quantitative analysis and operator bias is allowed, the value of quantitation per se is lost. We have developed a set of algorithms which allows full automation in the analysis of ventilation-perfusion studies and in the detection of left-to-right intracardiac shunting, and which except for the identification of the valve planes, allows full automation in the processing of nuclear angiocardiography (First Pass or ECG Gated) for LV function analysis

[en] An automatic thyroid disease diagnostic system was developed and is based on a unique approach to simulating human judgement. The intuitive judgement and knowledge of physicians is the basis for creating multiple judgement spaces to provide a diagnosis of thyroid diseases. The system can render judgements, for cases it has never before encountered

[en] A technique for making simultaneous dual x-ray energy scans on a conventional CT5005 is described. The only hardware modification involves the detector collimation where thin strips of tin foil are placed on alternate detectors. The effect of the foil is to increase the mean energy of the x-rays passing through the foil and consequently the detector readings for the covered detectors correspond to a higher energy scan than the uncovered detector readings. The two sets of detector readings are separated using software to obtain two sets of projection date from the one scan. These are processed in te usual way to give two final pictures at different x-ray energies. Two methods of converting these images to show the effective electron density and effective atomic number are reviewed. Chemical composition within a scan slice has been determined both in vitro and in vivo. A variety of clinical applications are under review. The most promising application to date has been the study of trabecular bone mineral loss in the elderly female