Feasibility and accuracy of left ventricular volumes and ejection fraction determination by fundamental, tissue harmonic, and intravenous contrast imaging in difficult-to-image patients.

The need to enhance the echocardiographic determination of left ventricular ejection fraction is greatest in patients with suboptimal images. Intravenous contrast (CON) and tissue harmonic imaging (THI) are 2 important methods for enhancing endocardial border definition. However, the comparative feasibility and accuracy of THI and contrast-enhanced power harmonic imaging in difficult-to-image patients have not been examined. We assessed the comparative accuracy of THI and CON in determining EF and ventricular volumes in patients with suboptimal fundamental images. We demonstrated that CON is feasible and exhibits a greater correlation with ejection fraction and ventricular volumes determined by radionuclide angiography (standard of comparison) than THI in this difficult-to-image population, with no reported side effects. For both ejection fraction and ventricular volumes, the observer variability was least for CON, intermediate with THI, and greatest for fundamental imaging.

Ultratag RBC kit for combined cardiac first-pass and multigated acquisition studies.

UNLABELLED: The authors developed a procedure to use the in vitro Ultratag (Mallinckrodt, St. Louis, MO) red blood cell (RBC) labeling kit for both first-pass (FP) and multigated acquisition (MUGA) studies with a high specific activity in a reduced volume (50 mCi/0.5 ml) and a high labeling efficiency that can be used with a single-crystal camera to yield a quality study. METHODS: A packed red blood cell (PRBC) bolus was created by two methods: (a) reducing the volume of the components of the Ultratag kit and (b) centrifuging the final dose volume. The labeling efficiency of each bolus was evaluated, each PRBC bolus was visually inspected for clots and percent hemolysis was assessed using a hemocytometer at 30 min, 1 hr and 2 hr postcentrifugation. RESULTS: Use of the first method, the 50% kit, provided the best results. However, the resulting volume from this kit only approached 1 ml, which is not clinically adequate for a first-pass study. In the second method, the total volume was centrifuged to form a PRBC bolus, which appeared to be stable in the syringe for at least 2 hr. A combined FP/MUGA study from a centrifuged 50% reduced kit was performed in one normal subject as a preliminary assessment of the clinical utility of this procedure. The image quality of the scan is diagnostically adequate. CONCLUSION: By using the in vitro Ultratag kit, a compact PRBC bolus was created that was stable in the syringe and could be reinjected safely into the patient for combined cardiac FP/MUGA studies.

Failure in labelling of red blood cells with 99mTc: interaction between intravenous cannulae and stannous pyrophosphate.

The effect of different methods of stannous pyrophosphate (SnPYP) administration on a modified in vivo technique for labelling red blood cells (RBCs) with 99mTc has been studied. Retention of 99mTc in the bloodstream was measured and parallel in vitro RBC labelling experiments were performed. After administration of SnPYP or a mixture of SnPYP and heparin via the metal needles of intravenous cannulae, the mean 30-min retentions of 99mTc were 96.8% (SD 8.6) and 95.3% (SD 12.4) respectively and the mean in vitro labelling efficiencies were 86.9% (SD 5.0) and 81.9% (SD 18.2) respectively. When the SnPYP was administered via teflon cannulae, the mean 30-min retention of 99mTc was 40.0% (SD 16.7) and the in vitro labelling efficiency was 18.7% (SD 27.0). Reduced RBC labelling and rapid clearance of 99mTc from the bloodstream were not explained by adsorption of stannous ion or pyrophosphate onto the teflon cannulae or retention of SnPYP in the cannulae. When labelling RBCs with 99mTc it is important that SnPYP is not injected via a teflon cannula.

A modified method for the in vivo labeling of red blood cells with Tc-99m: concise communication.

The rate of incorporation of Tc-99m into red blood cells pretinned in vivo was measured by collecting blood samples in stannous DTPA solution, which served as a competing ligand for Tc-99m. This collection technique permitted a measurement of high-affinity red-cell labeling efficiency at the instant of sampling. At 0.5 min after injection only 62% of technetium is tightly bound to the red cell; this rises to 94.5% at 10 min. Based on the graded labeling of the red cells, the in vivo labeling procedure was modified by isolating pertechnetate and red blood cells tinned in vivo in a syringe during the first 10 min of labeling. The pertechnetate is thus prevented from distributing to extravascular compartments, and 90% of the injected Tc-99m is firmly bound to red blood cells at the time of injection. In a series of 23 patients, seven were tested with the in vivo method and seven with the modified in vivo method, and nine patients were tested with each method on separate occasions. A decrease in gastric activity and improved image quality were found with the modified method compared with the standard method of in vivo red-cell labeling.

Autoradiographic comparison of 96Tc-pyrophosphate and 45Ca bone uptake.

To compare the skeletal distribution of calcium and pyrophosphate complexes, autoradiograms of the growing zone of 10-week-old rabbit femurs were performed. Due to its stability to chemical and enzymatic hydrolysis and to the relatively long half-life of the isotope, 96Tc-labelled pyrophosphate was used. Calcium uptake was studied with carrier free 45Ca. For both tracers, the blood supply plays a significant role by delivering the radiopharmaceuticals. In a second step their partition was governed by mixing in different bone structures: calcium was incorporated inside the bone trabeculae and the mineral mass whereas labelled pyrophosphate remained in linear patterns surrounding bone spicules.

Effect of coronary blood flow and site of injection on Tc-99m PPi detection of early canine myocardial infarcts.

The effect of blood flow and site of injection on Tc-99m PPi uptake in acute myocardial infarction was studied in a group of 24 dogs. Temporary (3 hr) and permanent LAO occlusion models were used. Animals with the temporary occlusions showed scintigraphic visualization of the infarcts and reversal of the normal epito-endocardial Tc-99m PPi ratio in contrast to those with permanent coronary occlusions. The data demonstrate that early (within 3 hr) experimental canine myocardial infarcts can be detected with Tc-99m PPi if reflow to the area of infarction is provided. Delayed development of abnormal Tc-99m PPi scintigrams with acute infarction is related primarily to the initial lack of adequate blood flow to the damaged tissue, with subsequent development of adequate collateral flow allowing delivery and uptake of sufficient amount of the radiopharmaceutical for in vivo scintigraphic detection of the damaged area(s).

Survival of red blood cells in rabbits after acute administration of unlabeled stannous pyrophosphate: Concise communication.

We investigated the possibility that acute administration of unlabeled stannous pyrophosphate may adversely affect red blood cells in the rabbit. Our method was similar to the in vivo labeling of RBCs with technetium-99m for blood-pool scanning. The investigation showed that dosages recommended in the literature produce no demonstrable difference between pre- and postdose RBC survival, which strongly suggests that the stannous content of the pharmaceutical is not harmful to red blood cells.