Johan Vandevivere

Imaging of large vessel vasculitis with (18)FDG PET: illusion or reality? A critical review of the literature data

Fluorine-18 fluorodeoxyglucose positron emission tomography (18FDG PET) plays a major role in the management of oncology patients. Owing to the singular properties of the glucose tracer, many patients suffering from non-malignant diseases such as inflammatory or infectious diseases may also derive clinical benefit from the appropriate use of metabolic imaging. Large vessel vasculitides such as giant cell arteritis and Takayasu arteritis are other examples that may potentially extend the field of 18FDG PET indications. The purpose of the present article is to assess the feasibility of metabolic imaging in vasculitis on the basis of the current literature data. In particular, the clinical context and the 18FDG imaging patterns seen in patients with large vessel vasculitis are analysed in order to identify potential indications for metabolic imaging.

Effect of mild mental stress on solid phase gastric emptying in healthy subjects

SummaryRadionuclide gastric emptying studies are performed in clinical routine but the possible influence of the mental state of the patient is never taken into account. We wanted to evaluate the effect of a mild psychological stress on solid phase gastric emptying in healthy young male volunteers. The standard meal consisted of a pancake (500 kj) without additional liquid. Simultaneous dynamic acquisitions of gastric activity in anterior and posterior projection were taken during 90 min starting from the onset of the meal. Gastric emptying was evaluated three times in basal conditions and once under mental stress. Stress was induced by means of a dichotomous listening test, lasting for 30 min, starting at the end of the meal. The results of rest and stress studies were compared. Mild mental stress has a significant influence on gastric emptying. The lag phase increased from 11±3 min to 36±10 min (mean±S.D.) (p < 0.005) and the gastric emptying rate from 79±13%/hour to 100±31%/hour (mean±S.D.) (not significant). During a stress period gastric emptying as a whole is delayed but this is mainly due to the prolongation of the lag phase. Our data also suggest that during the stress period gastric emptying is interrupted and reactivated once the stress period has ended.

Evaluation of reproducibility of solid-phase gastric emptying in healthy subjects

Radionuclide gastric emptying studies are performed as a matter of clinical routine. Our aim was to evaluate the inter- and intea-individual variability and the reproducibility of gastric emptying studies in healthy young male volunteers using a single solid-phase, standard meal. The meal consisted of a pancake (500 KJ) tagged with technetium 99m sulphur colloid and no additional liquid. Continuous acquisitions of gastric activity in anterior projection were taken during 90 min, starting from the onset of the meal. Gastric emptying was evaluated three times in a 3-week period. Five different parameters were evaluated. Our results show that there is important inter- and intea-individual variability in normal volunteers. In spite of this variability, no significant difference between the different series of gastric emptying studies was observed.

The evaluation of right ventricular performance using krypton-81m

The availability of krypton-81 m suitable for intravenous injection provides an easy means for assessing right ventricular function. The superimposition of the other heart chambers does not constitute a problem. The activity in the left heart is negligible and the study can be performed in the right anterior oblique position to obtain optimal separation between the right atrium and the right ventricle. Lung activity is quite high and should be corrected before computing the right ventricular ejection fraction. This correction can be accomplished by performing Tc-99m MAA perfusion scintigraphy. The measurement of the right ventricular ejection fraction appears to be reproducible with very small inter-and intraobserver variability. Good quality phase and amplitude images can be obtained with such high count rates.

Continuous anterior acquisitions in gastric emptying: comparison with the mean.

Depth correction is necessary when gastric emptying is studied by means of a labeled meal. In this study continuous anterior images were acquired from the onset of the food ingestion. Differences in depth were measured using a left lateral view. A minimal and crude depth correction was performed. The results obtained with this correction method were compared with those obtained using the depth correction technique of the mean. The results obtained in the anterior projection without any depth correction were also compared with those obtained using the method of the mean. The results obtained with both correction techniques were identical in 18 gastric emptying studies. This approach also permits the creation of a time-activity curve over the duodenum in the anterior projection. In this way the lag phase can easily be assessed.

Visualization of Brainstem Perfusion Using a High Spatial Resolution SPECT System

The authors explored the high spatial resolution of a three-head rotating SPECT system, equipped with lead super-fine fanbeam collimator. The brainstem was highlighted in a three-dimensional reconstruction, showing perfusion small structures such as mesencephalon, pons, and medulla oblongata. The visualization of brain-stem perfusion sets new landmarks in functional neuroimaging and, moreover, was obtained with a commercially available three-head SPECT system.

Radionuclide Venography Using Continuous Kr-81m Infusion: Preliminary Note

Continuous infusion of Kr-81m presents important advantages compared to the commonly used radionuclides for venography. High count rates can be accumulated, and a high resolution collimator can be employed to ensure good quality images. The study can be repeated immediately and multiple views can be performed until a satisfactory result is obtained. The production of radionuclide from a Rb-81--Kr-81m generator suitable for intravenous infusion is almost the same as that which is suitable for ventilation. The same generator can first be used for venography and then for ventilation imaging to complete the work-up patients suspected of having thromboembolic disease.

Performance of a single crystal digital gamma camera for first pass cardiac studies

First pass radionuclide angiocardiography (FPRNA) has gained increasing interest because of the development of new 99Tcm-labelled perfusion agents and of new 191Os/191Irm generator systems. The aim of the study was to evaluate the performance capacities of a small field of view single crystal digital gamma camera for 99Tcm and 191Irm at high count rates. The camera dead time for 99Tcm (window 30%) was well corrected up to 300 kcps in fast acquisition mode using the relative decrease of a small shielded reference source. Using the decaying activity method for 191Irm the non-linearity response of the gamma camera was corrected by an 191Os reference source up to 210 kcps at 70 keV, 75 kcps at 129 keV and 320 kcps including both peaks. Saturation count rates were respectively 270 kcps, 150 kcps and 420 kcps and high count rate resolution (FWHM) 9.0, 7.3 and 10.3 mm. Since the accuracy of first pass measurements is more sensitive to count rate than to spatial resolution the 50–150 keV window was chosen for clinical studies. In data obtained from 32 ECG gated FPRNA patient studies, the whole field of view count rate during the left ventricular phase ranged from 100 to 250 kcps with 80 to 120 mCi (2960–4400 MBq) of 191Irm and 100 to 180 kcps with 20 to 25 mCi (750–925 MBq) of 99Tcm red blood cells permitting for both tracers accurate non-linearity correction.

Unsuspected muscular radionuclide uptake due to chronic muscular injury contracted during sports activity.

Increased soft-tissue uptake is commonly encountered in metastases, infarction, vascular calcification, myositis ossificans, hemangiomas. In addition, injured muscles and rhabdomyolysis have an affinity for bone-seeking radiopharmaceuticals. Matin and co-workers even correlated the intensity of muscular tracer uptake with complaints in ultra-marathon runners. In this patient, however, the very intense muscular uptake, caused by repeated sport-induced injuries of a rather unusual origin, did not correlate with the complaints. Also, our case illustrates that even children are at risk for unsuspected traumatic lesions, contracted during sports or physical activity.

240 degrees: why not?

SummarySingle photon emission tomographic imaging of myocardial perfusion with 99Tcm-labelled agents is usually performed with single-detector gamma camera systems and 180° anterior data collection. With multi-detector systems, reconstruction over 180° and 360° has been reported. We used a data set of normal subjects to compare both reconstruction methods. In addition, we tested an alternative approach, reconstructing data from 240° acquisitions, excluding the right posterior views, which provide little myocardial information and which are responsible for a reduced signal-to-noise ratio. On the transverse slices, the known apical distortion with the 180° reconstruction was not noted with the 360° or 240° reconstructions. Using semi-quantitative analysis of apical, mid-ventricular and basal short-axis slices, almost complete overlap was observed between the 240° and 360° circumferential profiles of our 20 normal volunteers, except in the inferior wall where a reduction in activity was noted. However, this rinding was less pronounced with the 240° than with the 180° reconstruction. The frequent reduction in activity in the anterior wall was more prominent with the 180° than with the 240° and 360° reconstructions. A 240° acquisition represents a useful compromise between 180° and 360° imaging protocols when a single-detector device is used, allowing more homogeneous tracer distribution and a reduction in the apical distortion without material change of contrast or doubling of the acquisition time.