Aortic enhancement during abdominal CT angiography: correlation with test injections, flow rates, and patient demographics.

OBJECTIVE: The goal of our study was to determine the effect of contrast material injection rate and patient demographic variables on vascular enhancement for abdominal CT angiography and compare test injection results with actual patterns of vascular enhancement. SUBJECTS AND METHODS: One hundred twenty-five patients underwent abdominal CT angiography. For each patient, CT attenuation values (Hounsfield units) of the aorta were determined before and after IV contrast administration, every 3 sec between 21 and 60 sec. A peak aortic enhancement value and the time needed to reach peak and aortic enhancement thresholds of 150 and 200 H were determined. All patients received 150 ml of nonionic contrast material at 3 ml/sec in 25 patients and 4 ml/sec in 100 patients. A test injection of 15 ml was used to compute a scan delay in 46 patients. Patient age, sex, weight, injection rate, and test injection results were compared with vascular enhancement patterns. RESULTS: For the 125 patients, the mean aortic enhancement at each time point was greater than 150 H. Patient weight was inversely correlated (r2 = -.62) with aortic enhancement. The test injection did not accurately predict actual aortic enhancement peak value or time. Test injection delay time was significantly correlated with time to reach aortic enhancement thresholds of 150 and 200 H. The 4 ml/sec rate resulted in a higher peak aortic enhancement (320+/-58 H versus 281+/-49 H) (mean +/- SD, p < .01) that was reached quicker than with the 3 ml/sec injection rate (45+/-5 sec versus 52+/-5 sec) (p < .01). Injecting at 4 ml/sec resulted in greater aortic enhancement values at 24-45 sec, whereas 3 ml/sec produced significantly better aortic enhancement at 54-60 sec. CONCLUSION: The test injection correlated better with time to reach specific aortic enhancement thresholds than with time to peak aortic enhancement. For a given amount of contrast material, faster injection rates resulted in greater vascular enhancement that occurred earlier.

Liver metastases: early detection based on abnormal contrast material enhancement at dual-phase helical CT.

PURPOSE: To assess whether contrast material enhancement findings on computed tomographic (CT) scans are useful in determination of the risk for development of hepatic metastases. MATERIALS AND METHODS: Dual-phase helical CT scans were obtained in 80 patients with nonhepatic cancer and no hepatic metastases visible at CT. Attenuation was measured on scans obtained at 25 and 40 seconds. Peak liver attenuation was determined in all cases. Unenhanced scans were obtained in 35 patients. The ratio of liver attenuation at 25 and 40 seconds to peak liver attenuation, liver enhancement values at 25 and 40 seconds, and ratio of liver enhancement at 25 and 40 seconds to peak liver enhancement were determined. RESULTS: Liver metastases developed during 18-month follow-up in 22 patients. The 25- and 40-second liver enhancement values and the liver enhancement and attenuation ratios were higher in these patients than in those who did not develop metastases (P < .01). Enhancement values and ratios were more accurate than densitometric measurements for predicting development of metastases. Use of an optimal threshold (0.40 or greater) for the 40-second enhancement ratio resulted in a sensitivity of 75%, specificity of 96%, and overall accuracy of 89%. CONCLUSION: CT measurements may help in the prediction of risk for subsequent development of hepatic metastases.

Difference in global hepatic enhancement assessed by dynamic CT in normal subjects and patients with hepatic metastases.

PURPOSE: Our goal was to determine if there are differences in liver densitometry parameters using helical CT between normal subjects and subjects with liver metastases. METHOD: One-hundred fifty subjects (64 with normal livers and 86 with CT-visible hepatic metastases) underwent dual phase helical scanning of the liver. Images were obtained in the "arterial" (early) and "venous" (late) phases of hepatic enhancement. Densitometry measurements were obtained from the liver (distinct from obvious lesions or vessels) and aorta at 25, 40, 75, and 90 s. Enhancement values at the same time points were calculated in 73 subjects in whom noncontrast images of the liver were available. A peak liver densitometry value was also determined. Several ratios were determined for each time point: the liver/aortic ratio (L/A), liver/liver peak ratio (L/P), liver enhancement/aortic enhancement ratio (LE/AE), and liver enhancement/liver peak enhancement ratio (LE/LPE). The degree of tumor burden in the hepatic metastatic group was assessed in each case. RESULTS: Values for L/A, L/P, LE/AE, and LE/LPE at 25 and 40 s were significantly (p < 0.05) higher in the liver metastases group than the normal liver group. Enhancement ratios were even more elevated in breast cancer, which can have hypervascular metastases. These CT parameters did not show significant differences when analyzed according to the degree of hepatic metastatic tumor burden. All densitometry parameters and ratios obtained at 75 and 90 s were not significantly different between the two groups. CONCLUSION: In the early phase of bolus intravenous contrast agent administration, the visually normal portion of the liver parenchyma in patients with hepatic metastases enhances to a greater degree than the liver in normal subjects. This may reflect generalized increased hepatic arterial flow in tumor-bearing livers and has the potential to increase the sensitivity of CT for detection of hepatic metastases.

Assessment of renal function with computed tomographic densitometry measurements.

RATIONALE AND OBJECTIVES: We assessed the relationship between multiple renal computed tomographic (CT) densitometry parameters and renal function. METHODS: Three hundred seventy-three patients underwent standardized helical CT of the abdomen. The ratio of mean attenuation in the renal cortex to mean attenuation in the aorta (KAR), the products of mean renal cortical attenuation with CT-estimated renal volume (KVP), and the patient's weight (KWP) were derived from scans obtained 90 sec (n = 373) and 30 sec (n = 108) after initiation of intravenous contrast material administration. These densitometry parameters were compared with renal function measured by serum level of creatinine and creatinine clearance (CrCl). RESULTS: Among the 373 patients in the study, we found statistically significant differences (p < .01) between the patients with normal renal function (CrCl > or = 60 ml/min, n = 300) and the patients with abnormal renal function (CrCl < 60 ml/min, n = 73) for the KAR, KVP, and KWP. The KAR was the parameter best correlated with CrCl and was an independent predictor of renal function from the patient's age, weight, and renal volume. Fifty-three patients with a KAR less than 1 had significantly worse renal function (CrCl = 60 +/- 21 ml/min) than the patients with a KAR greater than or equal to 1 (CrCl = 95 +/- 31 ml/min). Only 4% of patients with normal renal function had a KAR less than 1. A threshold value of KAR less than 1 had a sensitivity of 55%, a specificity of 96%, a positive predictive value of 75%, and a negative predictive value of 90% for predicting renal dysfunction. CT parameters obtained at 30 sec were less useful than parameters at 90 sec. CONCLUSION: In patients undergoing clinically requested CT scanning, renal densitometry analysis can be used to depict patients with normal renal function; however, it has a high false-negative rate in depicting patients with diminished renal function.

Potential renal donors: comparison of conventional imaging with helical CT.

PURPOSE: To assess helical computed tomography (CT) as a potential substitute for intravenous urography and renal angiography in the evaluation of living potential renal donors. MATERIALS AND METHODS: Helical CT was performed in 32 potential donors both before and after administration of contrast material. Scans were reconstructed at 1.5-mm intervals for three-dimensional reconstructions. Helical CT images were blindly compared with urograms (n = 32) and renal angiograms (n = 24). RESULTS: One small accessory artery was not depicted with helical CT, and angiography did not depict an accessory artery arising in proximity to the origin of the main renal artery. All eight kidneys with early dividing main arteries were identified with both helical CT and angiography. Three renal venous anomalies were depicted only with helical CT. Helical CT and urography equally depicted nonvascular findings. CONCLUSION: Renal helical CT is a suitable replacement for intravenous urography and angiography in the assessment of living renal donors.