Regional pulmonary distribution of iodine-125-labeled oleic acid. Its relationship to the pattern of oleic acid edema and pulmonary blood flow.

Oleic acid infusion in dogs produces a patchy, predominantly peripheral lesion on CT scans. This study correlates the pattern of oleic acid injury with the distribution of infused oleic acid and pulmonary blood flow. Radiolabeled oleic acid (I-125, 0.05 ml/kg) and radiolabeled 15-micron microspheres (Co-57) were infused into the right atria of 11 dogs. Oleic acid was given after the microspheres in six dogs and before microspheres in five dogs. Ten minutes after infusion, the lungs were removed. Four transverse slices (0.5 cm thick) of the lower lobes were taken from each dog and cubed. Samples were grouped into three regions of the transverse slice: outer, middle, and inner concentric rings. In both groups, I-125 (oleic acid) activity was greater in the outer than the middle and inner concentric layers (P less than 0.001). When Cobalt-57 microspheres were given before oleic acid, Cobalt-57 activity was marginally lower in the outer layer compared with the middle and inner layers. However, when oleic acid was given first, microsphere activity in the outer layer was significantly lower (P less than 0.001) than the middle layer. Thus, oleic acid was preferentially distributed to the peripheral regions of the lung, similar to the regions of injury on CT. This distribution did not correspond to the pattern of pulmonary blood flow as indicated by the microspheres. Immediately after oleic acid infusion, pulmonary blood flow to the periphery was reduced, reflecting a response to the predominantly peripheral injury by oleic acid.

SPECT quantification of technetium-99m microspheres within the canine lung.

Attenuation compensated single photon emission CT (SPECT) count rates of 99mTc microsphere activities from 151 selected small regions of interest (ROIs) in an intact canine thorax were compared with the count rates obtained from scintillation camera images of similar ROIs from frozen slices of the thorax. A first-order method was used to compensate the SPECT and scintillation camera images for the effect of Compton scattering. The SPECT and scintillation camera count rates correlated well: r = 0.95 (RMS error 4.8 counts/s) for 19 X 19 X 13 mm thick ROIs. We conclude that regional quantification of 99mTc microspheres within the dog thorax is possible using camera-based SPECT systems.

Hydrostatic pulmonary edema. An analysis of lung density changes by computed tomography.

The computed tomographic (CT) appearance of pulmonary edema induced by elevated left atrial (LA) pressure was examined. Dogs, in the prone position, were scanned during suspended ventilation at functional residual capacity. A surgically implanted LA balloon was inflated to elevate LA pressure for 30 to 140 minutes to a mean pressure of 29.8 mm Hg. Lung water, measured gravimetrically, averaged 14.7 ml/kg body weight compared with 5.7 ml/kg in nonedema control dogs. Lung density in dogs with edema was 69.5% higher than base-line density, while in the control group final lung density was only 4% higher than base line. Analysis of regional density indicated that there were greater increases in density in more central and dependent (ventral) zones of the lung and relatively smaller increases in nondependent (dorsal) peripheral zones. These results are in contrast to the previously reported pattern of density change seen with oleic acid injury in which density increases were primarily in peripheral zones of the lung.

Analysis of the density of pleural fluid analogs by computed tomography.

A noninvasive method for differentiating transudative and exudative pleural effusions could make thoracentesis unnecessary in many cases. Since computed tomography (CT) can be used to measure tissue densities, it has a potential use in assessing density of intrathoracic fluid. This study was performed to test this possibility. Plastic syringes containing water, saline, and three saline-albumin solutions with densities up to 1.021 g/cc were scanned individually in air, in a chest phantom, and in a dog thorax during apnea. We found significant positive correlations between specific gravity and CT density; coefficients ranged from 0.85 to 0.99. Regression lines for the different test conditions were not statistically different. However, CT number variability, as indicated by the average standard deviation (SD), did differ for the test conditions: 1) Syringes alone, average SD was 3.8 HU; 2) chest phantom, average SD was 5.5 HU adjacent to rib and 5.8 HU anterior to vertebral column; 3) dog chest average SD was 19.2 HU with heart motion and 9.4 HU without heart motion. These results suggest that heart motion is a major factor in CT number variability in vivo, and that differentiation of transudates from exudates is not possible with current CT methods.

In vivo quantitation of regional cerebral blood flow in glioma and cerebral infarction: validation of the HIPDm-SPECT method.

Iodine-123 labeled hydroxyiodopropyldiamine (HIPDm) is a diffusible indicator with an 85%-90% extraction fraction and stable retention in the brain for more than 2 hr. Equilibrium-phase imaging and quantitation using single-photon emission computed tomographic (SPECT) scanning defined a distribution of HIPDm in proportion to regional cerebral blood flow (rCBF). Studies in calves affirmed a close correspondence (r = 0.97) in calculated rCBF between HIPDm and microspheres using the tissue deposition-arterial input function microsphere methodology. Using this same mathematical analysis in vivo, reproducible rCBF data within the expected range of normal were obtained on repeated studies in the same nonhuman primate. With a diffuse encephalopathy secondary to subarachnoid blood, a bilaterally symmetric decrease in rCBF was present. A prominent focal decrease in HIPDm accumulation and calculated rCBF was noted with cerebral infarction in the distribution of a ligated middle cerebral artery. Patient studies with glioma revealed diminished HIPDm accumulation due to decreased flow and/or pH in the region of the neoplasm as well as in the associated vasogenic edema and overlying gray matter.

Detection of pulmonary emboli in dogs: comparison of single photon emission computed tomography, gamma camera imaging, and angiography.

Single photon emission computed tomography (SPECT) allows separation of radionuclide activity in front of and behind the area of interest and results in more contrast than can be achieved using conventional gamma camera imaging. To determine if this improved contrast is of value in the detection of perfusion abnormalities in the lung, the lower lobe segmental pulmonary arteries of six dogs were embolized and pulmonary perfusion was evaluated using SPECT, conventional gamma camera imaging, and angiography. Although selective segmental angiography was the most sensitive method of detecting emboli, SPECT was much more sensitive than the gamma camera examination in evaluating the effects of the emboli at two hours and one, two, and eight weeks after embolization.

Muscarinic cholinergic receptor binding: in vivo depiction using single photon emission computed tomography and radioiodinated quinuclidinyl benzilate.

An attempt was made to characterize, in vivo, specific binding to the muscarinic cholinergic receptor in the calf using the radioiodinated ligand quinuclidinyl benzilate (123I-OH-QNB) and single photon detection emission computed tomography (SPECT). The supratentorial brain activity was significantly increased after the intravenous infusion of 123I-OH-QNB as compared to free 123I. Scopolamine, a muscarinic cholinergic receptor antagonist, decreased the measured brain activity when infused prior to 123I-OH-QNB consistent with pharmacologic blockade of specific receptor binding. Quantitative in vitro tissue distribution studies obtained following SPECT imaging were consistent with regionally distinct specific receptor binding in the striatum and cortical gray matter, nonspecific binding in the cerebellum, and pharmacologic blockade of specific binding sites with scopolamine. Although 123I-OH-QNB is not the ideal radioligand, our limited success will hopefully encourage the development of improved binding probes for SPECT imaging and quantitation.

In vivo regional quantitation of intrathoracic Tc-99m using SPECT: concise communication.

A whole-body single-photon emission computed tomographic system (SPECT) was used to quantitate the activities of a series of Tc-99m point sources in the dog's thorax and to evaluate attenuation of a uniform esophageal line source containing a known concentration of Tc-99m. A first-order attenuation correction and an empirically derived attenuation coefficient of 0.09 cm-1 were used in the SPECT analyses of the intrathoracic point sources. The relationship between SPECT measurements of multiple point-source activities and the same sources measured in air was linear over a range of 100 to 1000 muCi (slope 1.08; R2 coefficient of determination 0.97). These data are sufficiently accurate to allow an estimate of the regional activity of radiopharmaceutical in the dog's thorax and justify their use in experimental quantitation of regional pulmonary perfusion.

Radiographic quantitation of reversible blood-brain barrier disruption in vivo.

Cranial computed tomography (CT) was used to quantitate disruption of the blood-brain barrier (BBB) in dogs in vivo following intracarotid infusion of hypertonic mannitol. The degree of opening varied with the same dose and infusion rate. The ratio of contrast enhancement in brain vs. venous blood was elevated in 4 of 5 mannitol-treated animals, with the greatest enhancement occurring in the ipsilateral basal ganglia and cortical gray matter. The statistical significance and reproducibility of the derived CT numbers used for brain and venous blood calculations, as well as the linear relationship between iodine concentration and CT enhancement, was affirmed by obtaining multiple consecutive scans.

Experimental comparison of the thrombogenicity of fibrin and PTFE flow surfaces.

Two types of 4 mm ID prostheses were studied in the carotid arteries of the dog. These were noncrimped polypropylene-supported filamentous velour knitted Dacron (PPSFV) and expanded polytetrafluoroethylene (e-PTFE, Gore-Tex). Thrombus-"Free" Surface TFS) areas and patency rates were determined at the end of the implant periods. One series of implants was subjected to controlled low flow rates for six hours; another was exposed to physiologic flow rates and observed at seven days, 14 days, and 12 weeks. At six hours the filamentous Dacron, preclotted according to a specific regimen utilizating heparin, performed as well as, and possibly better than, e-PTFE. The Gore-Tex developed surface coagulum in an irregular fashion which was related to graft wetting and blood soakage. Seven-day TFS scores and patency rates of the two graft types were comparable at physiologic flow rates. At two weeks, TFS scores and patency rates of the two graft types were comparable at physiologic flow rates. At two weeks, TFS scores and patency rates dropped. This was sufficiently marked in the case of e-PTFE that longer-term implants were not done. However, PPSFV grafts were implanted for 12 weeks, and all grafts examined at that time had closed. It appears that patency of 4 mm ID grafts of this construction will not be reliably attained in the dog carotid artery without the use of platelet-inhibitory drugs until complete healing has occurred.

Current arterial prostheses. Experimental evaluation by implantation in the carotid and circumflex coronary arteries of the dog.

Five types of 4-mm diameter arterial prostheses (three Dacron, one expanded Teflon, one preserved umbilical vein) were studied in the dog to assess graft thrombogenicity. Separate experiments involving six hours of controlled blood flow, one-week carotid implantation, and aortocoronary implantation were performed. In general, graft thrombogenicity derived from controlled flow study was more predictive of a graft's long-term implantation success than were one-week implantation results. In order of increasing thrombogenicity, we ranked grafts studied as follows: noncrimped Dacron, expanded Teflon, crimped Dacron, umbilical vein. Results of 19 experimental left coronary artery implantations using Dacron or Teflon prostheses are reported that indicate grafts with low measured thrombogenicity are most likely to succeed in this site. Data presented in this report suggest there is reason to evaluate noncrimped, kink-resistant, porous Dacron grafts for use both in the left coronary artery and below the knee when there is compelling clinical indication and no autogenous vessels are available.

Melatonin: daily cycle in plasma and cerebrospinal fluid of calves.

Melatonin was measured by radioimmunoassay in jugular vein plasma and lateral ventricle cerebrospinal fluid collected from calves at 12 times of the day and night. Melatonin in cerebrospinal fluid increased 17-fold from an average (+/- standard error) of 38 +/- 8 picograms per milliliter during the day to an average of 637 +/- 133 picograms per milliliter during the night (P less than .001). Plasma concentrations of melatonin increased sixfold from an average, per milliliter, of 19 +/- 4 picograms during the day to 121 +/- 24 picograms during the night (P less than .001).