Beverly R. Bradley

Detection of hepatic malignancies using Mn-DPDP (manganese dipyridoxal diphosphate) hepatobiliary MRI contrast agent.

A new hepatobiliary contrast agent (Mn-DPDP) was used in the detection of liver metastases in six rabbits with seven hepatic V2 carcinomas. This contrast agent is derived from pyridoxyl-5-phosphate which is biomimetically designed to be secreted by the hepatocyte. After Mn-DPDP administration, a 105% increase in liver signal to noise was obtained using a 200/20 (TR/TE) pulsing sequence, and a 62% decrease in intensity was observed using a 1200/60 pulsing sequence. Liver V2 carcinoma contrast enhancement increased 427% using the 200/20 pulsing sequence and 176% using the 1200/60 pulsing sequence. Four of seven V2 carcinomas were not detectable prior to the administration of Mn-DPDP (50 mumol/kg). Two neoplasms were only detectable in retrospect (after Mn-DPDP) on the 1200/60 sequence. The smallest neoplasms detected in this study were 1-4 mm. Mn-DPDP appears to be a promising MRI contrast agent.

An Experimental Evaluation of Central vs. Peripheral Injection for Intravenous Digital Subtraction Angiography (IV-DSA)

At a given radiation dosage and field of view, five variables are under meaningful control for intravenous digital subtraction angiography (IV-DSA): concentration and quantity of contrast media injected, volume of injectate, rate of injection, and site of injection. Some controversy exists regarding the selection of a central vs. a peripheral injection site for IV-DSA. This study determined the influence of the site of injection on the peak and width of the arterial time-concentration curve produced by contrast media. Using a noninvasive, in vivo, quantitative x-ray measurement method, 36 separate injections (10 ml of ioxaglate at 8 ml/sec) were administered into the cephalic vein, subclavian vein, and main pulmonary artery in dogs. Injection sites were varied using a Latin-square experimental design. Cardiac output, central blood volume and the peak and width of the contrast media time-concentration curves were measured. The average peak enhancement was greatest for the pulmonary artery injection site. Normalizing peak and width values to make the pulmonary artery values 100%, the average peak values for injections into the subclavian vein and cephalic vein were 93% and 56%, and the average widths were 141% and 163%, respectively. These data support the use of a more central injection site for optimizing IV-DSA examinations.

Effect of volume and rate of contrast medium injection on intravenous digital subtraction angiographic contrast medium curves

The image quality of temporal (mask mode) intravenous digital subtraction angiography is directly dependent on the shape of arterial time-concentration curves produced by the intravenous injection of contrast medium. Curves that are narrow and tall minimize motion artifact (misregistration) and maximize contrast enhancement (pre- and postcontrast differences). To determine the effects of rate and volume of injection of contrast medium on intravenous digital subtraction angiographic curves, ioxaglate (Hexabrix), a monoacidic ionic dimer, was injected into large mongrel dogs. Quantitative measurements of opacification were made over time in the femoral arteries using a modified General Electric CT/T scanner. Peak opacification was directly proportional to the volume of contrast medium injected. Curve width was not affected by increasing volume of injection. At rates below a critical point, slower injection rates produced progressively shorter and wider arterial time-concentration curves. Above that critical point, increasing the rate of injection did not affect either curve width or curve peak.

Diameter of arterial microvessels trapping 8--10 micron, 15 micron and 25 micron microspheres as determined by vital microscopy of the hamster cheek pouch.

An assumption inherent in the use of microsphere methodology for measuring regional blood flow is that microspheres are removed from the circulation by impacting in arterial vessels of approximately their own diameter. We investigated the in vivo relationship between the diameter of varying size microspheres and the calibre of trapping microvessels within the hamster cheek pouch. Intracardiac injection of 8-10, 15 +/- 5, 25 +/- 5 micron carbonized microspheres with diversion of the cardiac output into the bracheocephalic trunk provided direct, in vivo visualization of the impaction sites of these various size microspheres within the cheek pouch microvasculature. Fifteen micron microspheres usually impacted at the orifice or neck of small arterioles and protruded into the lumen of the parent vessel. Eight to ten micron microspheres lodged in vessels with a mean diameter of 11.5 +/- SD 3.4 micron indicating that they usually impacted primarily in terminal arterioles.

The intraluminal distribution of 15-μ-diameter carbonized microspheres within arterial microvessels as determined by vital microscopy of the golden hamster cheek pouch ☆

Abstract An assumption inherent in the use of microspheres for measuring regional blood flow is that microspheres distribute uniformly with blood. Published studies suggest that carbonized microspheres, 15–80 μm in diameter, concentrate centripetally in blood flowing through medium-size arteries. The intraluminal distribution of carbonized microspheres within blood flowing through arterial microvessels is not known. To study this problem, the passage of 15-μm-diameter, carbonized microspheres through the arterial vasculature of the golden hamster cheek pouch was cinefilmed. The trajectories of 800 microspheres flowing through 24 vessel segments in 14 different golden hamsters ( Mesocricetus auratus ) were tabulated. The mean diameter of the observed arterial vessels was 65.2 ± 13.7 (SD) μm. Carbonized microspheres did not distribute homogeneously across the available lumen of the observed microarteries. Comparison of the experimentally determined microsphere distribution against a null hypothesis of a homogeneous density distribution showed a greater than expected concentration of microspheres at the periphery of the available lumen and a less than expected percentage at its center. This disparity was present whether a blunt velocity flow profile or a parabolic velocity profile was convoluted with the density distribution. If flow approximates the parabolic velocity profile, microspheres become markedly underrepresented at the center of the vessel and overrepresented at its periphery. The greater than expected centrifugal distribution of microspheres was related neither to vessl diameter nor to the microsphere velocities studied. If one assumes that erythrocytes are evenly distributed throughout the available arterial lumen (with the exception of a cell-free zone at the periphery), then 15-μm-diameter carbonized microspheres significantly underrepresent the central concentration of erythrocytes and overrepresent the concentration of red blood cells at the microarterial periphery.

Quantitative evaluation of left ventricular function using computed tomography.

Computed tomography (CT) provides a noninvasive technique with high resolution cross-sectional tomographic images which allow volume measurements of an object, independent of its geometric configuration. A phantom of known volume with controllable periodic motion was used to validate the CT method of volume determination. A good correlation (P less than 0.05) was achieved. Missing angle reconstruction algorithms for gating were applied to estimate left ventricular volumes and ejection fraction in an experimental animal, and the results compared with a standard angiographic method. Left ventricular volumes correlated poorly, whereas the ejection fraction obtained correlated well (r = 0.9). The discrepancies may be attributed in part to the CT method in which difficulties were recognized in defining the left ventricular borders at the base of the heart and partial volume effect, and in part to inaccuracies in the standard angiographic method. Once validated, this method has been applied to the animal model in the form of a pilot study.

Microsphere Distribution in Normal and Tumor-Bearing (DMBA-Induced Carcinogenesis) Hamster Cheek Pouch

This study evaluates, for the first time by direct visualization, the microvascular distribution of microspheres in normal hamster cheek pouch and in hamster cheek pouch bearing tumor induced by 7, 12 Dimethylbenz (A) Anthracene solution (DMBA). In contrast to the results of the previously used open-chest technique, this carotid injection technique does not lead to irregular distribution of 15-mu carbonized microspheres, chain, or impaction phenomena. It is concluded that methodology differences may account for different results.

Flow determination using computed tomography: application to aortic dissection. Part II.

Dynamic CT is not only useful in imaging an aortic dissection but may provide additional information concerning the hemodynamic significance of differing flow patterns in the false channel compared with the true channel. Once validated, the computed tomographic (CT) method of flow determination (See Part I) was applied to an experimental animal model with a surgically created aortic dissection. Good correlation was obtained for the flow estimates of cardiac output derived for the true and false channel (r = .82). The shapes of the curves, however, were distinct, reflecting different flow patterns for the true and false channels. Curve parameters, such as peak CT number (P = .0001), variance (P = .006), and, in particular, the number of mixers (a parameter used to quantify the degree of mixing) (P = .0001), demonstrated significant differences between the two channels of the dissection. The curve parameters derived can therefore be used to differentiate the true and false channels and may then predict the long-term outcome of the false channel, and the aortic branches derived from it.

Variability of myocardial CT measurements in vivo.

Variability of myocardial CT measurements, as indicated by standard deviations of mean CT numbers from four myocardial regions, was compared in 12-second scans, 3-second scans, and gated end-diastolic and end-systolic images, all from the same 12 seconds of scan data, both without and with radiographic contrast enhancement in experimental animals. There were statistically significant differences (P less than 0.05) in standard deviations of myocardial CT measurements when comparing 3-second and 12-second scans without contrast (10.4 vs. 7.7 CT#s), and 12-second scans without and with contrast (7.7 vs. 11.2 CT#s). Standard deviations of mean myocardial CT measurements were significantly greater (P less than 0.01) in gated images (end-diastolic) when compared with 12-second scans, both without contrast (22.2 vs. 7.7 CT#s) and with contrast (20.2 vs. 11.2 CT#s). In this study variability of myocardial CT measurements increased as scan time decreased, with radiographic contrast enhancement and with gating cardiac images.

Sequential Feline Esophageal Nutrient Blood Flow Perfusion Measurements In Vivo

The utilization of a catheter semiconductor beta detector (CASRAD) to perform in vivo, sequential, esophageal nutrient blood flow distribution studies in cats is described. A diffusable radioisotope, Rubidium 86 (86Rb), was injected intravenously and the CASRAD placed within the esophageal lumen. The distribution of 86Rb remained stable within the feline esophagus for sufficient time to allow for counting at 1.5 cm levels in the esophagus. The accuracy limitations of the CASRAD system were assessed by comparing the in vivo, recorded distribution of 86Rb with the esophageal distribution of 86Rb as determined by a well-type scintillation counter. The distribution throughout most of the esophagus was similar by both techniques. Sequential esophageal studies performed with the CASRAD showed less variability than existed in the biological differences between cats and the methodology of obtaining and counting tissue by well-type scintillation counter (mean coefficient of variation 11.6% versus coefficient of variation 23.1%).