Saadia Cochavi

Assessment of Regional Myocardial Perfusion by Positron Emission Tomography after Intracoronary Administration of Gallium-68 Labeled Albumin Microspheres

Position emission computed tomography (ECT) of the normal and ischemic canine heart was undertaken in eight anesthetized dogs after the intracoronary administration of 68gallium labeled human serum albumin microspheres (SAM). Bolus doses of 200 μCi of 68Ga-SAM were injected into the left anterior descending (LAD) and left circumflex coronary arteries of four normal dogs and four dogs undergoing LAD ligation. Positron imaging of 68Ga-SAM distribution was performed with a multicrystal positron camera and computer reconstruction. In normal dogs, five to six axial transverse section images of the heart demonstrated the transmural distribution of 68Ga-SAM in an annular pattern around the left ventricular cavity. In dogs with LAD ligation, perfusion defects in the anterolateral wall and septum were observed in tomographic cuts through ischemic areas. In conclusion, these studies demonstrate the feasibility of positron ECT imaging of the heart after intracoronary administration of 68Ga-SAM.

Preliminary imaging results with 18f-2-fluoro-2-deoxy-D-glucose

Transverse section imaging with 18F-2-fluoro-2-deoxy-D-glucose (2FDG) is of considerable interest because quantitative values of regional glucose metabolism may be obtained. We present preliminary results using 2FDG produced by the Brookhaven National Laboratory and imaged with the PCII at the Massachusetts General Hospital. Three studies are reported showing the distribution in dog, monkey, and in brain of an essentially normal patient.

Positron emission tomographic imaging of the myocardium with 81Rb.

An approach to the assessment of regional myocardial perfusion has been developed utilizing positron emission tomographic imaging of the heart after intravenous administration of 18Rb (T1/2 = 4.6 hr) and a multicrystal positron camera. In five intact anesthetized dogs, 1.0 to 2.0 mCi of 81RbCl was administered and imaging begun 5 min later. A total of 7 to 9 transverse section images of the heart (1 cm thick) were obtained by the computer reconstruction of 208 images taken at uniformly spaced angles as the camera was rotated 180° around the animal. Collection time was 18 min. Emission images of 81Rb activity were corrected for attenuation by first obtaining transmission data using a planar positron-emitting source. Transverse section images through the apex of the heart showed uniform uptake of 81Rb+ activity below the left ventricular (LV) cavity. Tomographic images through the midventricular level showed myocardial 81Rb+ distribution in an annular pattern around the LV cavity, and tomographic cuts through the base of the heart showed a horseshoe appearance of activity anteriorly and diminished tracer uptake posteriorly in the region of the left atrial wall. These studies demonstrate the feasibility of three-dimensional myocardial imaging by using the 33% positron emission of 81Rb+ and a positron camera.

Transverse Section Imaging with Carbon-11 Labeled Carbon Monoxide

The inhalation of small quantities of carbon-11 labeled carbon monoxide results in a useful red cell label to identify vascular structures in the body and quantitate red cell concentration in tissues. Transverse section images are obtained using PC-II, the Massachusetts General Hospital (MGH) Positron Camera. Attenuation correction is performed either by means of transmission data or by analytical methods. Sets of transverse section images give information on red cell distribution in head and torso. Such images may be useful in identifying vascular abnormalities or in quantitating red cell physiology.

Positron Imaging Instrumentation

Positron imaging systems provide a unique and powerful means to examine the spatial and temporal course of radiopharmaceuticals in the body to observe normal and abnormal physiology in vivo. The information so obtained in conventional or transverse section mode complements the information on structure obtained from conventional x-ray and computerized tomography (CT) imaging. Powerful instruments are now available to provide high resolution conventional and transverse section positron images.

Detection of pulmonary emboli by positron imaging of inhaled 15O-labeled carbon dioxide*

A new radionuclide approach to the scintigraphic detection of pulmonary emboli is described. This method utilizes cyclotron-produced C15O2, administered by inhalation, for rapid labeling of pulmonary blood. Following clearance of oxygen-15 from the lungs by pulmonary blood flow, focal retention of activity results from stasis of blood distal to emboli. On serial positron imaging, focally retained activity delineates embolized pulmonary segments and identifies the location and extent of pulmonary emboli. In animal studies this positron scintigraphic method detected emboli as small as 2 mm in diameter. In patients with suspected pulmonary emboli, this approach appears to be both sensitive and specific. Clinically, C15O2 inhalation imaging is most useful for the detection of pulmonary emboli in patients with chronic lung disease or congestive heart failure. It is rapid and safe and can be easily repeated, with minimal radiation exposure, for determining resolution rates of emboli and for assessing residual blood flow distal to emboli.

TRANSVERSE SECTION IMAGING WITH THE MGH POSITRON CAMERA PC-II

Transverse section emission imaging provides a method to quantitatively measure physiological parameters on a three dimensional basis in the body. PCII, the MGH Positron Camera, is widely used for such studies. New instruments promise higher sensitivity and resolution. The ultimate instrument would use as many of the annihilation events occurring with the body as possible.