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.

Monitoring radiation dose to the hands in nuclear medicine: location of dosemeters.

The relatively high radiation dose which can be received by the hands of staff in nuclear medicine departments means that in many departments it is necessary to monitor such doses. A convenient method is to use a TLD sachet in a plastic strip around a finger. This study was done to determine whether a dosemeter worn at the base of the middle finger was adequate to monitor the dose to the surface of the whole hand. Dosemeters were worn at the finger tips, finger base and palm of both hands, on two people while preparing and dispensing radio-pharmaceuticals, and two others while giving injections using syringe shields. The pattern of distribution of radiation does to the hands was similar for all workers and for both types of work. A single, convenient site (base of middle finger) may therefore be used for monitoring radiation dose to the hand.

The use of radionuclide bone scintigraphy to determine local spread of oral squamous cell carcinoma to mandible.

In oral squamous cell carcinoma, conservative resection of mandible is not recommended if there is tumour invasion. The use of bone scintigraphy to obtain a more accurate assessment of tumour spread has been evaluated in comparison with radiographs and histology in 11 patients. Tumour invasion of bone was shown on scans and radiographs, but periosteal reaction to tumour was detected by scintigraphy only. Thus both scintigraphy and radiography are recommended for preoperative assessment of bony margins for radical resection.

New technique for showing the relation of tomographic myocardial perfusion images obtained with thallium-201 to the coronary arteries.

A new technique has been developed for presenting myocardial tomograms that allows the observer to perceive the shape of the thallium-201 distribution directly. The surface of the myocardium was found by applying an interactive thresholding technique to a set of conventional transverse slices. Computer graphics techniques were used to display a shaded image of that surface on a television screen, showing the three dimensional shape of the myocardial surface from any chosen aspect. A set of normal preserved coronary arteries was digitised, and using scaling and transformation techniques these arteries were mapped on to the myocardial tomograms and a shaded surface image produced with superimposed coronary arteries. This provided a familiar anatomical framework for locating perfusion defects. Its value in identifying various diseased vessels was confirmed by a comparison of the tomographic findings with the angiographic findings in five individual cases.

Quantitative analysis of rotating gamma camera thallium-201 scintigrams of myocardium.

Detection of defects in myocardial uptake of thallium-201 has been investigated by tomography with a rotating gamma camera. Twenty patients, 17 of whom had symptoms suggestive but not diagnostic of angina, and three with definite angina, underwent exercise ECG testing. Thallium-201 was injected at peak stress, followed by tomographic imaging with 180 degree data collection. A repeat study 4 h later showed the resting blood flow (redistribution) pattern. Transverse, coronal and sagittal sections were reconstructed and stress and redistribution studies compared. Quantitative comparison of T1-201 uptake in the stress and redistribution sections was investigated using profile analysis. These results were compared with a visual assessment. Tomographic images clearly showed defects in myocardial uptake and enabled scans to be classified definitely as normal, ischaemic or showing previous myocardial infarction. Results agreed with those from exercise ECG where ECG findings were definite, and gave a clear diagnosis in cases with equivocal ECG results. Significant differences were demonstrated between stress and resting uptake profiles for all segments judged ischaemic on stress from the images alone. A 'normal' profile was obtained to permit identification of infarcted regions. While quantitative analysis enabled the tomograms to be classified objectively, qualitative assessment was equally effective in nearly every case, possibly due to the clear and unconfusing image presentation.