The Aberdeen Mark II single-photon-emission tomographic scanner: specification and some clinical applications.

The construction, operation and physical characteristics of a single-section multi-detector single-photon-emission scanner are described. The machine has 24 detectors arranged along the sides of a square. Movements and data collection are under the control of a series of distributed microprocessors. Both head and trunk tomograms can be produced. The spatial resolution at the collimator focus is 9 mm in the transverse plane, and the effective slice thickness is 14 mm. The volume sensitivity is 300 counts/s kBq ml with a 20 cm diameter cylindrical phantom filled with 99Tcm solution. The application of this machine to the examination of the brain, liver and heart has been found to be clinically useful.

A comparison of three systems for performing single-photon emission tomography.

A comparison is made between the performance of three transverse axial single-photon emission tomographic machines, namely a rotating gamma-camera and two different scanning systems. Each system has been evaluation in terms of the spatial resolution, sensitivity and efficiency. The functional dependence of the volume sensitivity on the size of the emitting object has been derived using a theoretical model of the photon emission, attenuation and detection. The model is shown to predict this size dependence well and is consistent with the experimental observations.

A clinical trial of the value of a tomographic section view to identify liver abnormalities by radionuclide imaging, with special reference to metastatic disease.

A prospective trial was carried out to assess the value of a radionuclide transverse section view in addition to conventional radionuclide scans of the liver. Reports for 373 patients were analysed and compared with the final independent clinical diagnosis. Although several individual cases were more accurately diagnosed using the tomographic section view, the trial did not demonstrate a significant increase in accuracy of diagnosis in liver disease. Some possible reasons for this are discussed, mainly the difficulty of identifying and quantifying truly abnormal features of liver radioisotope scans.

Contribution of radioisotope CAT to the detection of recurrent tumour in the brain.

Two cases are described showing the value of Radioisotope Computerized Axial Tomography in the early detection of tumour recurrence in the brain. The possibility of recurrence could not be excluded from the information provided by the conventional views since the suspicious areas found could be due to post-operative uptake. In the first case, reliable identification of tumour recurrence was provided by the transverse section scan through the suspicious area. In the second case, the transverse scan showed the uptake to be due to previous craniotomy.

Cranial scintigraphy: value of adding emission computed tomographic sections to conventional pertechnetate images (512 cases).

A prospective trial was carried out to assess the contribution made by a radionuclide transverse-section view to conventional radionuclide scans of the brain. Each set of scans was reported by two independent teams of observers, but only one team viewed the tomography section. An abnormality rating was used to decide whether a set of scans was positive or normal. The reports for 512 patients were analyzed and compared with the final independent diagnosis. Greater accuracy of diagnosis with the section view was significant at the 0.1% level; the results showed that failure to detect tumors was almost halved while there was a 16% improvement for the detection of infarcts. Abnormality ratings were also used to plot ROC curves and rating curves; these showed that the addition of the tomographic view increased markedly the proportion of true positives without any increase in the proportion of false-positive reports.

An assessment of computerised isotopic renal section scanning.

The basic non-invasive investigation of renal space occupying lesions by excretion pyelography was coupled with ultrasonic scanning. Forty-one patients who have undergone isotopic section scanning as part of their investigative assessment were studied. The conditions investigated included solitary cysts, polycystic kidneys, renal tumours, tumefactive xanthomatous pyelonephritis, renal infarct and non-functioning kidneys. An analysis of the accuracy of isotopic section scanning in these different pathological states was made. Computerised isotopic section renal scanning offers a new non-invasive renal investigative technique.

Evaluation of x-ray CT (EMI scan) and isotope brain studies, including radioisotope axial tomography.

A comparison is made of the results of computer-assisted X-ray tomography (EMI scan) and those of radionuclide brain scan supplemented by computer-assisted isotope tomography. The X-ray examination shows a wider range of positive diagnosis, but the radionuclide examination is complementary in the detection of supratentorial gliomas. A similar comparative value of the isotope tomogram is noted in the detection of cerebral infarcts.

An evaluation of transverse axial emission tomography of the brain in the clinical situation.

The Aberdeen section scanner provides, in addition to conventional views, a display of the distribution of radioactivity in a tomographic section of the brain. This paper examined the value of this additional information. Scans of lesions confirmed pathologically or radiologically, along with normal and doubtful cases, were examined after a careful randomization procedure. During the course of the study each set of conventional views was examined twice, once without and once with a tomographic section view. In two out of 29 cases (7%) the lesion was diagnosed only with the aid of the tomographic section scan. Improved accuracy of diagnosis with the tomographic section view was significant at the 1% level or better.

Diagnostic value of computerised isotopic section renal scanning.

Isotope section renal scanning in the diagnosis of kidney disease has been compared with ultrasonic examination adn specialised radiological techniques. The computerised isotope tomographic section technique developed in Aberdeen has increased the accuracy and differential diagnosis of renal lesions especially cysts and tumours.

A practical approach to transverse-section gamma-ray imaging.

The object of transverse-section gamma-ray imaging is to display the concentration of radioactive material in a thin transverse slice of the body. The technique is essentially that of reconstructing a density distribution from its projections, and many methods have been developed to perform the reconstruction. This report describes the realization of three such methods, using a small digital computer PDP8 I, and their application to experimental and clinical data obtained from the Aberdeen Section Scanner: (1) simple back projection; (2) the convolution method of Bracewell and Riddle; (3) the linear integral transform method of Radon. The problems of sensitivity variation and attenuation are examined. An approximate attenuation correction procedure is described. The reconstruction method of Bracewell and Riddle was found convenient since then the data were manipulated in a manner where smoothing to reduce statistical noise and correction for absorption could both be readily incorporated.