A physical comparison of two fixed-angle emission tomographic cardiac imaging systems

The optimum technique for 201T1 tomography of myocardium: an investigation using phantoms

Rotating gamma-camera tomography is the method of choice for 201Tl perfusion imaging to detect myocardial ischaemia or infarction, but the optimum technique has not previously been investigated. Variables which can affect the utility of the images include acquisition time, collimator sensitivity and resolution, spatial filtering, reconstruction matrix and display parameters. An 'Iowa' design myocardial phantom containing 201Tl, with a defect representing an unperfused area, was used to study the effect of these variables. Results were assessed by measuring image contrast and non-uniformity and by observer grading trials. Receiver operator characteristic (ROC) curves and contrast ratios indicated that filtering the acquisition data with a count-dependent (Metz) filter before reconstruction and using a narrow slice width gave best results. No single collimator was superior for all four defect locations investigated but low-energy general purpose and high-resolution collimators were preferred to those with greater sensitivity. Reducing acquisition time by a factor of four compared with that for routine patient imaging affected contrast ratio, uniformity and area under ROC curves insignificantly, provided the optimum reconstruction was used. Displaying tomographic sections in colour gave no improvement in ROC curves over monochrome images. Data acquisition time or administered 201Tl radioactivity might therefore be reduced below the 25 min and 80 MBq often used for patient studies.

Thallium-201 scintigraphy for ischaemic heart disease and infarct detection: comparison of rotating slant-hole tomography and planar imaging

A trial was undertaken to compare the diagnostic capabilities of rotating slant-hole tomography and raw scintigraphic planar images for the assessment of ischaemic heart disease and for infarct detection. Twenty patients with coronary artery disease established by arteriography and 29 patients who had suffered acute myocardial infarction as established by ECG and enzyme criteria were imaged, along with ten normal volunteers. Overall sensitivity and specificity figures, as well as Receiver Operating Characteristics (ROC) curves, were obtained. For infarct detection there was a sensitivity of 93% for tomography and 96% for planar imaging while the specificity was 80% for tomography and 95% for planar imaging. This loss of sensitivity and specificity was also apparent in the ROC curves and showed that there was no advantage from the use of rotating slant-hole tomography. For ischaemic heart disease the sensitivities for tomography and planar imaging were 83% and 91% respectively, while the specificities were 83% and 90% respectively. The ROC analysis again showed this reduction in the diagnostic capability of the test. It was concluded that rotating slant-hole tomography was no advantage in the assessment of ischaemic heart disease. Inter-and intra-observer variability was good with consistent responses in more than 90% of cases. No significant improvement was demonstrated in the poor ability of thallium scanning to specify the diseased vessels, and the phenomenon of false defects in the rotating slant-hole tomographic scans of some normal subjects was shown to affect the response of observers significantly.