Quantitation of local cerebral blood flow and partition coefficient without arterial sampling: theory and validation.

A new technique that requires neither arterial blood sampling nor prior knowledge of the indicator's tissue-blood partition coefficient has been developed for quantitation of local CBF. This technique arises from an existing method that uses the inert, freely diffusible gaseous tracer [18F]methyl fluoride (CH3(18)F) and positron computed tomography. The shape of the arterial blood curve is derived from continuous sampling of expired air. The concentration of CH3(18)F in the arterial blood is assumed to be proportional to the expired gas curve interpolated between end-tidal values. The absolute scale of the blood curve is determined by fitting a series of venous blood samples to a multicompartment model. Four validation studies were performed to compare values derived using the venous scaled expired breath input function with those derived using direct arterial samples. The proposed method gave higher flow values than the standard arterial sampling method by an average of 4.4%. These validation studies and data from both normal and patient scans suggest that the method provides the quantitation necessary for interstudy comparisons yet avoids the trauma of an arterial puncture.

Determination of regional cerebral blood flow in patients with cerebral infarction. Use of fluoromethane labeled with fluorine 18 and positron emission tomography.

Regional cerebral blood flow (rCBF) was determined using the tissue kinetic of fluoromethane labeled with fluorine 18 and positron emission tomography (PET) in 13 normal subjects and 21 patients with cerebrovascular diseases. The mean brain rCBF was 42.9 +/- 4.3 mL/100 g/min during the resting state. The highest rCBF (60 +/- 8 mL/100 g/min) was noted in the mesial occipital region corresponding to cortical area 17. All 17 cases of cerebral ischemic infarcts had depressed rCBF in the hemisphere ipsilateral to the infarct. Every area of decreased density shown in the conventional computed tomograms (CT) was detected on the PET as an area of decreased rCBF (mean rCBF of infarcted area, 14.3 +/- 6 mL/100 g/min). The PET images showed a wider area of depressed rCBF than the region of the anatomic infarct. Five types of remote effects were noted in areas without structural damage: (1) decreased flow in the thalamus and caudate ipsilateral to the infarct; (2) decreased flow in the hemisphere contralateral to the cerebral infarct; (3) decreased flow in the cerebellar hemisphere contralateral to the cerebral infarct; (4) decreased flow in the visual cortex distal to the optic radiation lesion; and (5) decreased flow in the frontal cortex ipsilateral to the infarct. The effects in the contralateral hemisphere and the cerebellum were present only in the acute postictal phase. In four cases of transient ischemic attacks, rCBF was normal. It is concluded that this technique of measuring rCBF is a reliable method of identifying cerebral ischemia and that the determination of the extent of impaired rCBF provides a more accurate assessment of the region of brain dysfunction than CTs.

The rim sign: association with acute cholecystitis.

In a retrospective analysis of 218 hepatobiliary studies in patients clinically suspected of acute cholecystitis, a rim of increased hepatic activity adjacent to the gallbladder fossa (the "rim sign") has been evaluated as a scintigraphic predictor of confirmed acute cholecystitis. Of 28 cases with pathologic confirmation of acute cholecystitis in this series, 17 (60%) demonstrated this sign. When associated with nonvisualization of the gallbladder at 1 hr, the positive predictive value of this photon-intense rim for acute cholecystitis was 94%. When the rim sign was absent, the positive predictive value of nonvisualization of the gallbladder at 1 hr for acute cholecystitis was only 36%. As this sign was always seen during the first hour postinjection, it can, when associated with nonvisualization, reduce the time required for completion of an hepatobiliary examination in suspected acute cholecystitis.

Inclusion of physiologic data into computerized nuclear medicine dynamic studies.

A general technique has been developed for the multiplexing of time-dependent analog signals into the individual frames of a scintillation camera dynamic function study. A pulse train, frequency-modulated by the physiologic signal, is injected into a test input of a preamplifier servicing an outer phototube of the camera head. These tail pulses mimic photoevents occurring at a point outside of the camera's field of view, chosen to occupy a data cell in an unused corner of a computer-stored image. By selecting a region of interest encompassing this pulser peak, the resulting time-activity curve displays the desired physiologic variable in temporal synchronism with the radiotracer distribution.

Experimental approaches to myocardial function studies: C15 O2 and 81m Kr.

The role of short-lived gaseous radiotracers in myocardial function studies is reviewed. The evaluation of shunts and ejection fractions characterizing individual chambers is best performed with tracers restricted to those chambers. Classic examples include the C15 O2 inhalation radiocardiogram for probing the left-heart performance, with the right heart illuminated by intravenous 133Xe in saline. A more elegant utilization of rapid physical decay to unravel flow patterns is seen in the use of 81m Kr. Krypton-81m is swept from its parent 81Rb, either confined to an extracorporeal generator or an in vivo rubidium distribution. The steady-state images that result contain a wealth of dynamic information distilled into its most lucid format.

Estimation of absolute left ventricular volume from gated radionuclide ventriculograms. A method using phase image assisted automated edge detection and two-dimensional echocardiography.

Twenty-four patients underwent gated cardiac blood pool (GBP) imaging, two-dimensional echocardiography (2-D echo), and single-plane contrast ventriculography (within 24 hours). Variable left ventricular (LV) regions of interest on GBP images were identified by an automated threshold radial search. To avoid excluding LV counts we indexed the search threshold to the threshold identified by a phase image generated by Fourier analysis. LV depth calculated by 2-D echo was used for attenuation correction of LV counts. LV end-diastolic volume (EDV) and end-systolic volume (ESV) were calculated by dividing attenuation, background and deadtime corrected LV count rates by the background corrected count rate/ml of venous blood drawn during the study. Correlations between radionuclide and contrast volumes were good (EDV + ESV r = 0.97, EDV r = 0.94, ESV r = 0.95). Regression lines were close to the lines of identity. This method, in which GBP imaging and automated LV edge finding are complemented by 2-D echo for count attenuation correction, demonstrated reliable and reproducible noninvasive estimates of absolute LV volume.

Influence of respiratory maneuvers on jugular venous reflux.

The cause of jugular venous reflux during a radionuclide cerebral angiogram is uncertain. The authors describe a patient in whom physiologic respiratory maneuvers had a profound influence on the jugular venous reflux during cerebral radionuclide angiography. The massive jugular reflux was abolished by intravenous injection of a radiotracer bolus during inspiration. When brain blow data are difficult to interpret because of reflux, the authors suggest that radiotracer be administered intravenously during inspiration.

Metastatic calcification: the role of bone scanning.

Metastatic calcification involving the lungs and stomach was demonstrated in 3 patients by bone scans. In one patient, postmortem studied five days later confirmed the findings. Follow-up scans in 2 patients, demonstrating improvement in one and worsening in another, paralleled the clinical course.

Use of a generalized modular data handling system in nuclear medicine.

Addition of a CAMAC modular data handling system to a small computer used for gamma-camera work has allowed the acquisition and processing of a broad variety of nuclear medicine data. Significant contributions have been made ranging from clinical renal evaluation to radiopharmaceutical development. Digital rectilinear scanning and computer acquisition of physiological signals such as the electrocardiogram are other applications. The system provides an inexpensive means of matching present-day nuclear computers to the diversity of data.

Dual radiopharmaceutical imaging in congenital asplenia syndrome.

Asplenia was suspected in one patient with combined immunodeficiency syndrome and 5 with congenital cardiac anomalies who had Howell-Jolly bodies on peripheral blood smears. 99mTc-sulfur colloid scans were equivocal for absence of the spleen. When they were compared with the 99mTc-PIPIDA hepatobiliary images, a discrepancy in organ morphology between the two scans indicated that the spleen was present, whereas similarity of the two images suggested asplenia. This procedure was useful in establishing asplenia in 4 patients and confirming the presence of a rudimentary or ectopic spleen in 2 others. Unequivocal demonstration of the spleen on the sulfur colloid scans makes the hepatobiliary study unnecessary, while unequivocal demonstration of a normal-appearing liver without splenic activity may warrant a tagged red-cell study for a more complete evaluation.