J. A. K. Blokland

Positron emission tomography: a technical introduction for clinicians.

Up to a few years ago, positron emission tomography (PET) was known as a very expensive research tool using positron emitting radiopharmaceuticals to study metabolic processes in vivo. Recent developments in detector technology enabled the detection of the distribution of positron emitting radionuclides inside the human body through dual-headed gamma camera systems. These much cheaper cameras did move the focus of PET from research to clinical applications. The improved availability of [(18)F]fluorodeoxyglucose has promoted clinical PET. Ongoing developments in detector and image reconstruction technology may lead to even more accurate imaging in the clinical setting. New applications in diagnosing and staging of cancer patients came across and more will arise. In this paper, we present a short historical overview and a technical introduction of PET.

Aspects of fetal thyroid dose following iodine-131 administration during early stages of pregnancy in patients suffering from benign thyroid disorders.

Abstract. Detrimental effects on the thyroid of the developing fetus as a result of iodine-131 treatment for thyrotoxicosis of the mother in the first trimester of pregnancy are discussed. Dose estimations under typical clinical circumstances yield a fetal thyroid dose of 100– 450 Sv. This dose may increase considerably if the blood concentration of 131I in the mother remains high. Under such circumstances there may be fetal thyroid dysfunction, which can lead to severe abnormalities.

Influence of angiotensin converting enzyme inhibition on pump function and cardiac contractility in patients with chronic congestive heart failure.

Eleven patients with coronary artery disease and chronic heart failure were studied before and three months after the angiotensin converting enzyme inhibitor enalapril was added to their frusemide medication. The following were measured: left ventricular pressure and volume with transient occlusion of the inferior vena cava, radionuclide angiography, and hormone concentrations in plasma. As in other reported studies, the clinical condition of the patients improved and their exercise tolerance increased moderately. Addition of enalapril reduced end diastolic and systolic pressure, reduced ventricular volume, and concomitantly increased the ejection fraction. The end systolic pressure-volume relation shifted to the left as it did in a similar animal study. In the animal study unloading by a vasodilator did not induce a leftward shift, so it can be inferred that in the present study unloading combined with a decrease in the angiotensin concentration was instrumental in remodelling the heart. Though unloading was expected to have a beneficial effect on the oxygen supply/demand ratio of the heart, the patients still showed the same drop in the ejection fraction during exercise as they did before treatment with enalapril, and early diastolic filling did not improve. Normally, regression of cardiac dilatation is only found if pump function improves; the present study showed that unloading in combination with angiotensin converting enzyme inhibition reshapes the ventricle without improving intrinsic pump function.

Value of magnetic resonance imaging in patients with a recent myocardial infarction: Comparison with planar thallium-201 scintigraphy

The diagnostic accuracy of spin-echo Magnetic Resonance (MR) imaging in the detection and localization of a recent myocardial infarction (mean 4 days old) was compared to planar thallium-201 scintigraphy in 20 patients with a documented myocardial infarction. A control group of 10 subjects underwent a similar MR imaging procedure without thallium-201 scintigraphy. T1-weighted MR images (TE 30 msec) showed abnormal thinning of the infarcted left ventricular wall during systole (<50% of the opposite wall) in 11 patients (55%). On T2-weighted multi-echo MR images, (TE 30–60–90–120 msec) abnormally increased signal intensity was found in 17 patients and coincided with the location of the infarction. Thallium-201 scintigraphy detected the infarction in 18 patients. Comparison of T2-MR imaging and thallium-201 scintigraphy showed concordant findings in 82% of the left ventricular segments. In 9% of segements, thallium uptake was reduced with normal T2-MR and in 9% we found a normal thallium uptake with abnormal T2-MR findings. In all subjects of the control group, T1-MR images were normal, and only one subject showed increased signal intensity on T2-MR images. We conclude that the diagnostic accuracy of MR imaging in detecting a myocardial infarction is similar to that of T1-201 scintigraphy.

Magnetic resonance imaging of myocardial infarction: Correlation with enzymatic, angiographic, and radionuclide findings

Spin-echo cardiac magnetic resonance imaging studies were performed in 20 patients with a first 7- to 14-day-old (mean 10) myocardial infarction. The magnetic resonance imaging findings were compared with coronary angiography (14 patients), myocardial enzyme release (18 patients), radionuclide angiography (19 patients), and thallium-201 perfusion scintigraphy (19 patients). Regional T2 relaxation times determined from the signal intensities at echo times 30 msec and 90 msec were significantly prolonged in the infarcted areas. Based on abnormal T2 times for every patient, a regional and a total myocardial damage score was determined. The infarct-related artery was correctly identified in 93% of patients by magnetic resonance imaging, in 79% of patients by thallium-201 scintigraphy, and in 62% of patients by radionuclide angiography. The total damage score correlated well with enzymatic infarct size (r = 0.75, p less than 0.001). The correlation between left ventricular end-systolic volume index determined by magnetic resonance imaging and by radionuclide angiography was r = 0.89 (p less than 0.002). The left ventricular end-systolic volume index correlated significantly with enzymatic infarct size (r = 0.72, p less than 0.001), total damage score (r = 0.68, p less than 0.002), and radionuclide left ventricular ejection fraction (r = -0.68, p less than 0.002). Correlations between the magnetic resonance damage score and the thallium-201 perfusion score were r = 0.60 (p less than 0.01) for the exercise images, and r = 0.72 (p less than 0.001) for the redistribution images. This study shows that spin-echo magnetic resonance imaging is quite comparable with the established noninvasive imaging modalities currently used in patients with acute myocardial infarction.

The effects of diltiazem on cardiac function in silent ischemia after myocardial infarction

In a total group of 56 patients with an acute myocardial infarction who were maximally exercised at predischarge, 20 patients (36%) showed greater than or equal to 1 mm asymptomatic ST-T segment depression during exercise. The site of the infarction was anterior in 12 patients and inferior in eight patients. All 20 patients underwent repeated exercise radionuclide angiography 2 days later, 2 hours following oral intake of 120 mg of diltiazem. Double product was not significantly different before and after diltiazem, both at rest and during exercise. Maximal ST-T depression after diltiazem was reduced from 2.3 +/- 0.8 to 0.7 +/- 0.6 mm (p less than 0.01). Left ventricular (LV) ejection fraction at rest before diltiazem was 54.4 +/- 8.7% and after diltiazem was 56.2 +/- 11.3% (p = NS). During exercise, LV ejection fraction improved after diltiazem from 43.2 +/- 12.2% to 49.8 +/- 10.5% (p less than 0.05). Regional wall motion score (1 = normal, 2 = hypokinetic, 3 = akinetic, 4 = dyskinetic) at rest before diltiazem was 9.6 +/- 2.0 and after diltiazem was 9.1 +/- 1.8 (p = NS). During exercise, regional wall motion score improved after diltiazem from 5.8 +/- 1.3 to 4.3 +/- 1.1 (p less than 0.02). We conclude that silent ischemia occurs in a substantial number of patients after myocardial infarction and that diltiazem has acute beneficial effects on asymptomatic ST-T depression and on global and regional LV function in post-infarction patients with silent ischemia.

Short‐Term and Long‐Term Changes of Left Ventricular Volumes During Rate‐Adaptive and Single‐Rate Pacing

SEDNEY, M.L, et al.: Short‐Term and Long‐Term Changes of Left Ventricular Volumes During Rate‐Adaptive and Single‐Rate Pacing To evaluate the adaptation of the heart to exercise during pacing, 15 patients with permanent endocardial pacemakers were studied; nine patients had atrioventricular universal (DDD) pacemakers (Symbios 7005) and six patients had activity detecting rate‐responsive ventricular (WIR) pacemakers (Activitrax 8403). Left ventricular function in each patient during rate variable pacing was compared to ventricular function during VVI single‐rate pacing. End‐systolic and end‐diastolic volume changes during exercise were measured by radionuclide angiography and the amount of volume change was used to assess left ventricular function. Both short‐term (within 4 hours) and long‐term measurements (after at least 4 weeks) were made at rest and at 50% of the maximal exercise capacity in DDD or VVIR mode and were compared with VVI single‐rate pacing. All patients, when changed from DDD or VVIR mode to VVI single‐rate pacing showed a significant increase of the end‐diastolic volume during exercise, which increased even more after long‐term VVI pacing. During long‐term rate variable pacing, there was no increase of the end‐diastolic volume during exercise. DDD or VVIR pacing initially showed a substantial increase of the end‐systolic volume during exercise combined with a decrease of left ventricular ejection fraction, suggesting a decrease of the left ventricular contractility. After 4 weeks, contractility improved both with DDD and VVIR pacing. We conclude that short‐term DDD and VVIR pacing induces a temporary impairment of left ventricular function that improves after 4 weeks, whereas long‐term VVI pacing is associated with left ventricular dilatation even at moderate levels of exercise.

Automatic region of interest determination in dual photon absorptiometry of the lumbar spine

In a heuristic approach, the authors developed an algorithm for automatic region-of-interest (ROI) determination in bone mineral density (BMD) measurements of the lumbar spine. First, the algorithm detects the boundaries of the spine utilizing simple smoothing and gradient operators followed by a dynamic programming technique. Second, it selects L2, L3, and L4 from the spine by examining the BMD values along lines that are orthogonal to the local direction of the spine. The algorithm was tested in studies of a spine phantom, normal subjects (30), and patients (94). In all but two patient studies of severely affected spines the contours were detected correctly. The ROI determination was performed satisfactorily in all studies of the phantom, normals, and patients that had no spinal fractures. The coefficient of variation (CV) in the phantom studies was equal to 0.7%. In duplicate studies of 15 normal subjects and nine patients, the CV was equal to 1.0 and 2.7%, respectively. Compared to manual determination of the ROI, the precision of BMD measurements was clearly improved by the automatic procedure.

A breathing lung phantom for 81mKr lung ventilation studies its use in dosimetry and quality control

The construction of a breathing lung phantom that can be used to measure the amount of radioactive gas in the lungs as well as to determine the absorbed dose is described. For a lung ventilation study that consists of 6 views of 300 kents each, an effective dose equivalent of 50 μSv was calculated. The phantom is also suitable for comparison of different generator systems.

Aspects of performance assessment of whole body imaging systems

Abstract.Regular quality control is one of the cornerstones of nuclear medicine and a prerequisite for adequate diagnostic imaging. Many papers have been published on quality control of planar and tomographic imaging systems. Up to now, however, only minor attention has been given to the assessment of the performance of whole body imaging systems. In this paper we present a comprehensive set of test procedures including acceptance testing and regular quality control. It is not our purpose to present a thorough analysis of the methods and results. The selection of the tests is discussed and the tests are described; some results are presented. In addition action thresholds are proposed. The quality control tests can be applied to systems with either a moving detector or a moving imaging table, and to both detectors with a large field of view and detectors with a small field of view. The tests presented in this paper do not require special phantoms or sources other than those used for quality control of stationary gamma cameras. They can be applied for acceptance testing and for performance testing in a regular quality assurance programme.