Antonio C. Brito

Determination of liver, kidney, and spleen volumes by computed tomography: an experimental study in dogs.

Abstract: The volume of the dogs liver, kidneys, and spleen were measured by computed tomography (CT) and a water displacement method. Organ volume determination by CT is a rapid, simple procedure that is accurate to ±5% of the organ volume measured by water displacement. Individual measurements were reproducible to within ±3%. Determination of organ volume has potential importance in a variety of clinical situations.

Absolute Lung Density in Experimental Canine Pulmonary Edema

The noninvasive quantification of pulmonary edema could be of importance in patient management. We have developed a portable Compton-scatter densitometer capable of measuring density in the range of 0.1-1 g/cm3 independently of the chest wall. Change in lung density was investigated in 19 dogs with pulmonary edema induced by a combination of raised left atrial pressure and hemodilution. The increase in lung density correlated with the postmortem assessment of lung water (r = 0.862, p less than 0.01) and with hemodynamic indicators of pulmonary edema (r = 0.749, p less than 0.01). Subtracting the intravascular component of lung density did not improve the correlation with postmortem lung water (r = 0.850, p less than 0.01). The measurement of absolute lung density by a Compton-scatter technique may be a potentially useful method of quantifying pulmonary edema.

Computed Tomography of Splenic Subcapsular Hematomas: an Experimental Study in Dogs

Following baseline CT scans, splenic subcapsular hematomas were produced in dogs by direct splenic trauma. The CT scans of the spleen were obtained one to two hours before and after administration of IV contrast media and one, two, seven, 14 and 28 days following splenic trauma. Variations in the CT image of the hematomas was correlated with time and alterations in the chemical and histologic nature of the hematoma. Initially, the hematomas were isodense with the normal spleen and identified only following IV contrast administration. The initial number of hematomas identified by CT decreased to about half after seven to 14 days and then remained stable. Analysis of the hematomas revealed an initial increase in hemoglobin which was followed by a decrease. Dry weight increased, then decreased; lipid content decreased over time; and calcium content showed no appreciable change. The CT appearance of splenic subcapsular hematomas is dependent on the age of the hematoma. CT scans done soon after trauma should be performed following administration of intravenous contrast media, while less acute hematomas should be apparent without contrast media. Changes in attenuation values of hematomas appear due to a reduction in hemoglobin content and an increase in water content of the hematoma.

Use of Thermography to Predict Intestinal Viability and Survival After Ischemic Injury: A Blind Experimental Study

Reactive hyperemia is a characteristic of viable ischemic tissue that has been revascularized. In 14 normal dogs, segments of bowel were made ischemic for periods of 2--8 hours. Thermograms and surface temperature measurements of exposed ischemic and nonischemic segments were obtained before and every 5 minutes for 30 minutes after revascularization. Thermograms demonstrated uniform reactive hyperemia throughout the segments ischemic for 2--3 hours; hyperemia with some nonuniform, patchy areas in segments ischemic for 3--7 hours; and no hyperemic response in segments ischemic for 8 hours. All five dogs demonstrating uniform hyperemia survived and the bowels were found to be histologically normal. Four of the six dogs showing hyperemia with some nonuniform areas survived, but all six showed areas of transmural damage with fibrosis and scarring histopathologically. The three dogs with no hyperemic response died of pathologically proved bowel infarction. Our results indicate that thermograms can document the degree and extent of reactive hyperemia. Thermograms, therefore, may be an important aid in assessing bowel viability during surgery.

In Vivo Measurement of Hepatic Iodine Concentration Using Fluorescent Excitation Analysis

Hepatic iodine concentration was measured in the live dog by external use of fluorescent excitation analysis. The number of characteristic photons produced by interaction of exciting radiation from an americium-241 source with iodine within the tissue is proportional to the tissue iodine concentrations. A correction is made for absorption of radiation by the abdominal wall and other tissues lying between the volume of liver being assayed and the detector collimator. The technique is applicable to the in vivo measurement of iodine concentrations from 0.5 to 40 mg/g. Accuracy of the technique is approximately +/- 10%, which is within the range of variation in iodine concentration at various sites within the liver. Radiation dose is low, and radiolabeled tracer compounds need not be used.

Computed tomography of experimental acute renal ischemia.

The potential role of computed tomography (CT) in the detection of acute renal ischemia was assessed in nine mongrel dogs. Ischemia was produced by inflation of a balloon catheter in the main renal artery, with scans performed before, during, and after a 60-minute period of ischemia. A small but consistent increase in the attenuation value of ischemic renal parenchyma was observed. When intravenous contrast material was given, the ischemic kidney was markedly less enhanced than the contralateral, nonischemic kidney. By using the contralateral kidney for comparison, the ischemic kidney could be identified with or without the use of a contrast agent. Although calculations of mean pixel values were necessary when a contrast agent was not injected, the abnormal kidney could be easily recognized from the CT images themselves when intravenous contrast material was given. Because of the consistency with which the abnormalities were observed, we recommend a clinical trial of CT in suspected acute renal ischemia.

Thermographic assessment of intestinal viability following ischemic damage.

Reactive hyperemia has been shown to be a characteristic of viable ischemic tissue that has been revascularized. A segment of small bowel was made ischemic by arterial occlusion and the ischemia maintained for 2 1/2 hrs (ischemic, viable bowel) or 8 hrs (ischemic, nonviable bowel) before circulation was restored. Thermograms and surface temperature measurements of exposed ischemic and non-ischemic bowel segments were obtained before and every five minutes after revascularization. Thermograms of segments revascularized after 2 1/2 hrs of ischemia demonstrated reactive hyperemia and a one to four degree increase in surface temperature compared to normal surrounding bowel. No hyperemic response was seen in bowel segments that were ischemic for 8 hrs. Our results indicate that thermograms can document reactive hyperemia of an exposed ischemic bowel that has been successfully revascularized and may be an important aid in assessing bowel viability during surgery.

Radionuclide imaging of bowel infarction complicating small bowel intussusception in dogs.

Technetium-99m (99mTc)-pyrophosphate was investigated for use as an indicator of intestinal infarction in intussuscepted bowel. Irreducible intussusceptions were created in eight adult mongrel dogs. Technetium-99m-pyrophosphate was then injected intravenously 24 and 48 hrs later for external scanning. In six of the dogs, infarction developed in the intussusception, and each demonstrated increased uptake of 99mTc-pyrophosphate on in vivo scintiscans. The two dogs without infarction showed no increase uptake of the radionuclide. Well-counting and specimen scanning confirmed increased radionuclide in the infarcted intussusceptions. These observations suggest that 99mTc-pyrophosphate is a reliable indicator of the vascular compromise that sometimes occurs with intestinal intussusception.

The effect of acute pulmonary edema on pulmonary vascular resistance: significance for the interpretation of dilated upper lobe vessels on chest radiographs.

Dilation of upper lobe pulmonary vessels is an important radiographic sign of acute, left heart failure. A prominent theory is that perivascular edema causes increased resistance at the lung bases and inverts the normal perfusion gradient such that upper lobe blood flow exceeds lower lobe flow. This theoretical increase in flow is thought to cause dilatation of upper lobe vessels. Previous experimental studies determined indirectly changes in resistance from changes in the perfusion gradient: Results were contradictory. We measured directly the effect of edema on resistance in isolated canine lungs. Resistance increased linearly with edema. The magnitude of increase was small, however, and insufficient to cause inversion of the perfusion gradient. Our data indicate that interstitial pulmonary edema does not cause significant redistribution of blood flow. We suggest that dilated upper lobe vessels are veins acting as pulmonary venous manometers, reflecting elevated left atrial pressure, not increased blood flow.