Effectiveness of abdominal compression during helical renal CT.

RATIONALE AND OBJECTIVES: The authors performed this study to assess the effect of abdominal compression on opacification and distention of the proximal renal collecting system during helical computed tomography (CT). MATERIALS AND METHODS: Abdominal compression was applied during helical CT in 31 patients who were scanned 150 and 300 seconds after initiating a dynamic bolus injection of contrast material. Two reviewers assessed renal collecting system opacification and measured the maximal short-axis diameter of the collecting system at three locations: the upper pole, the lower pole, and the proximal ureter. A similar evaluation was performed in a control group of 29 patients who underwent CT without compression at 300 seconds after initiating the injection of contrast material. RESULTS: Both reviewers noted collecting system opacification at all locations in 52 of 56 noncompressed collecting systems scanned at 300 seconds, 57 of 59 compressed collecting systems scanned at 300 seconds, but only 26 of 59 compressed collecting systems scanned at 150 seconds. Measured collecting system distention was statistically significantly greater at 300 seconds in patents who received compression than in patients who did not (P = .0013). For patients who received compression, measured collecting system distention was statistically significantly greater on scans obtained at 300 seconds than on scans obtained at 150 seconds (P = .0001). CONCLUSION: Abdominal compression during renal helical CT produces a detectable increase in renal collecting system distention. In patients who receive compression, scanning at 300 seconds rather than at 150 seconds results in greater collecting system distention and more consistent opacification.

Assessment of the clinical utility of the rim and comet-tail signs in differentiating ureteral stones from phleboliths.

OBJECTIVE: This study was designed to assess interobserver variability in identifying the rim and comet-tail signs and to determine the clinical utility of these signs in determining whether or not the calcifications with which they are associated represent ureteral calculi. MATERIALS AND METHODS: Two radiologists and a radiology resident, unaware of the final diagnosis, reviewed preselected helical CT images from renal stone examinations in patients with 65 indeterminate pelvic calcifications. Assessment of calcifications for rim or comet-tail signs was performed independently of an assessment for the following five secondary signs of urinary tract obstruction: caliectasis, pelviectasis, ureterectasis, perinephric stranding, and renal enlargement. Agreement in identifying rim and comet-tail signs was assessed by obtaining kappa statistics. The utility the of rim or comet-tail signs in determining whether ureterolithiasis was present in patients in whom perinephric stranding and ureterectasis were present or absent was determined. The frequency with which one or more of each of the five assessed secondary signs was identified ipsilateral to a calcification having rim or comet-tail signs was also tabulated. RESULTS: Kappa values for interobserver agreement ranged from 0.49 to 0.73. In only one patient was a rim sign detected in the absence of ureterectasis and perinephric stranding. Reviewers identified at least three of the five assessed secondary signs ipsilateral to calcifications showing a rim sign in all but one patient (by each radiologist) and four patients (by the resident). When three or more secondary signs of obstruction were seen ipsilateral to a calcification having a comet-tail sign, in all but one instance, this was because the calcification was a ureteral calculus or because there was a separate ipsilateral ureteral calculus. CONCLUSION: In many instances, observers did not agree about whether the rim and comet-tail signs were present. The rim sign was observed in the absence of any secondary signs of urinary tract obstruction in only one (1.5%) of the 65 patients in our series (95% confidence interval, 0-5.3%). The comet-tail sign, when accompanied by secondary signs of obstruction, should indicate that an ipsilateral ureteral stone is present and not the reverse.

Multi--detector row helical CT of the pancreas: effect of contrast-enhanced multiphasic imaging on enhancement of the pancreas, peripancreatic vasculature, and pancreatic adenocarcinoma.

PURPOSE: To determine the optimal phase for enhancement of the normal pancreas and peripancreatic vasculature and the maximal tumor-to-pancreatic parenchymal enhancement difference by using multiphase, contrast material-enhanced, multi-detector row helical computed tomography (CT). MATERIALS AND METHODS: Forty-nine patients with a normal-appearing pancreas but suspected of having pancreatic abnormality and 28 patients with proved pancreatic adenocarcinoma underwent multiphase, contrast-enhanced, multi-detector row CT during the arterial phase (AP), pancreatic parenchymal phase (PPP), and portal venous phase (PVP). Attenuation values of the normal pancreas, pancreatic adenocarcinoma, celiac and superior mesenteric arteries, and superior mesenteric and portal veins were measured during all three imaging phases. Quantitative analysis of these measurements and subjective qualitative analysis of tumor conspicuity were performed. RESULTS: Maximal enhancement of the normal pancreatic parenchyma occurred during the PPP. Maximal tumor-to-parenchyma attenuation differences during the PPP and PVP were equivalent but greater than that during the AP. Subjective analysis revealed that tumor conspicuity during the PPP and PVP was equivalent but superior to that during the AP. Maximal arterial enhancement was seen during the PPP, and maximal venous enhancement was seen during the PVP. CONCLUSION: A combination of PPP and PVP imaging is sufficient for detection of pancreatic adenocarcinoma, because it provides maximal pancreatic parenchymal and peripancreatic vascular enhancement. AP imaging can be reserved for patients in whom CT angiography is required.

Bladder tumor detection at virtual cystoscopy.

PURPOSE: To investigate the utility of computed tomographic (CT) virtual cystoscopy in the detection of bladder tumors. MATERIALS AND METHODS: Twenty-six patients suspected or known to have bladder neoplasms underwent CT virtual and conventional cystoscopy. The bladder was insufflated with carbon dioxide through a Foley catheter. Helical CT of the bladder was then performed. The data were downloaded to a workstation for interactive intraluminal navigation. Two radiologists blinded to the results of conventional cystoscopy independently reviewed the transverse and virtual images, with consensus readings for cases with discrepant results. RESULTS: Thirty-six (90%) of 40 bladder lesions proved at conventional cystoscopy were detected with a combination of transverse and virtual images. Four (10%) of 40 bladder lesions, all smaller than 5 mm, were undetected. Transverse and virtual images were complementary, since six polypoid lesions smaller than 5 mm depicted on the virtual images were not seen on the transverse images. In contrast, areas of wall thickening were more readily appreciated on transverse images. CT with patients in both supine and prone positions was necessary, since seven (19%) and five (14%) of 36 lesions were seen only on supine and prone images, respectively. CONCLUSION: CT virtual cystoscopy is a promising technique for use in bladder tumor detection of lesions larger than 5 mm. Optimal evaluation requires adequate bladder distention with the patient in both supine and prone positions and interpretation of both transverse and virtual images.

Sensitivity of CT scout radiography and abdominal radiography for revealing ureteral calculi on helical CT: implications for radiologic follow-up.

OBJECTIVE: We compared the sensitivity of CT scout radiography with that of abdominal radiography in revealing ureteral calculi on unenhanced helical CT. MATERIALS AND METHODS: Over a 6-month period, patients presenting to the emergency department with acute flank pain were examined with standard abdominal radiography and unenhanced helical CT, which included CT scout radiography. In 60 patients in whom a diagnosis of ureteral calculus was made, CT scout radiographs and abdominal radiographs were examined by two interpreters who assessed whether stones could be visualized. All CT scout radiographs were viewed on a workstation using optimized window settings. RESULTS: CT scout radiography and abdominal radiography revealed 28 (47%) and 36 (60%) of 60 ureteral calculi, respectively. All ureteral calculi that appeared on CT scout radiography also appeared on abdominal radiography. However, eight calculi that were visible on abdominal radiography were not visible on CT scout radiography. CT scout radiography and abdominal radiography revealed 28% and 46% of 39 calculi less than or equal to 3 mm in diameter, respectively. For 21 calculi larger than 3 mm, the sensitivity of CT scout radiography and abdominal radiography was 81% and 86%, respectively. CONCLUSION: Abdominal radiography is more sensitive than CT scout radiography in revealing ureteral calculi; however, some calculi revealed on unenhanced helical CT cannot be seen on either abdominal radiography or CT scout radiography. Ureteral calculi not visible on either study can only be followed, when necessary, with unenhanced helical CT.

Diagnosis of pulmonary embolism: comparison of CT angiography and MR angiography in canines.

PURPOSE: To compare the sensitivity and specificity of helical computed tomographic angiography (CTA), CTA with multiplanar reconstructions (MPR)/three-dimensional-shaded surface display (3D-SSD), and gadolinium-enhanced magnetic resonance angiography (MRA) for pulmonary embolism (PE) detection. MATERIALS AND METHODS: Gelatin sponge emboli were introduced into the femoral veins of seven dogs and conventional digital subtraction angiography (CA), CTA, and MRA performed. Images from CTA, CTA with MPR/3D-SSD, and MRA were reviewed for the presence of PE in lobar and segmental arteries, and subsegmental zones. Postmortem angiography and CA were the gold standard. RESULTS: There were 50 emboli in the 294 vessels/zones analyzed. The sensitivity of CTA for the two readers was 76% (95% confidence interval [CI]; 64%-88%) and 64% (95% CI; 50%-78%), and for the two MRA readers was 52% (95% CI; 38%-66%) and 48% (95% CI; 34%-62%). CTA was more sensitive than MRA when PE were subdivided by vessel caliber. Specificity was high for CTA and MRA among all readers (98.8%-99.6%). MPR/3D-SSD did not improve results of axial CT. MRA perfusion defects were 46% and 47% sensitive and 100% specific. Interobserver agreement was high for CTA and MRA (kappa 0.92 and 0.93, respectively). The average diameter of vessels with emboli was 3.7 mm +/- 1.06. CONCLUSION: Helical CTA is more sensitive than three-dimensional gadolinium-enhanced MRA for the detection of PE. Both CTA and MRA are highly specific for PE detection and demonstrate high interobserver agreement. MPR/3D-SSD did not increase CTA performance over axial images alone.

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.

Helical CT evaluation of potential kidney donors: findings in 154 subjects.

OBJECTIVE: The purpose of our study was to assess renal helical CT (RHCT) as the primary imaging technique in the evaluation of potential kidney donors. SUBJECTS AND METHODS: Unenhanced and enhanced (3-mm collimation) RHCT was performed in 154 kidney donors using 125-150 ml of i.v. contrast material at an injection rate of 3 or 4 ml/sec and a pitch of 1.3-2. Scans were reconstructed at 1.5-mm intervals for a three-dimensional image. RHCT images were compared with the results of renal arteriography (RA) (50 subjects) and surgery (117 subjects). RESULTS: CT and surgical findings agreed in 95% of patients (111/117), with five cases of missed accessory arteries (all < 2 mm in diameter) and one case of a missed early division of the main artery. In the 50 subjects who underwent CT and RA, imaging revealed concordance in 96% of 100 kidneys. One small accessory artery was not detected by CT (origin from the common iliac artery). RA did not detect accessory arteries in three subjects. All 22 kidneys with early dividing main arteries (< 1.5 cm from the aortic origin) were identified by both RHCT and RA. Axial and three-dimensional CT images were complementary: five small accessory arteries were seen well only on the axial sections, whereas four early dividing arteries and two cases of renal artery stenosis were prospectively identified only on the three-dimensional images. Twenty-five renal vein anomalies were detected only by CT. In the full series of 154 subjects, nonvascular renal findings included renal calculi (n = 11), cysts (n = 12), duplicated ureters (n = 6), horseshoe kidney (n = 1), and pelvic kidney (n = 1). CONCLUSION: RHCT can be the primary imaging technique in the assessment of potential kidney donors, reducing the number of examinations as well as the risk and cost of imaging in these subjects.

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.

Duplex Doppler evaluation of acute renal obstruction.

Patients with possible acute renal obstruction often undergo numerous types of radiological examinations. Renal Doppler ultrasound is a quick and noninvasive way to assess for physiological and hemodynamic changes that accompany acute obstruction. The renal Doppler study may provide unique data not available from conventional sonography. Most, but not all, clinical and laboratory studies regarding Doppler of acute renal obstruction have reported encouraging results. As limitations to the Doppler examination in this clinical setting are delineated, a proper role for renal Doppler will continue to emerge.

Lupus nephritis: predictive value of conventional and Doppler US and comparison with serologic and biopsy parameters.

PURPOSE: To compare conventional and Doppler ultrasound (US) with clinical and biopsy parameters used to assess disease activity and outcome in lupus nephritis and to assess the predictive value of US. MATERIALS AND METHODS: Thirty-four patients with lupus nephritis prospectively underwent laboratory and US analysis at the time of renal biopsy. US parameters were renal length, relative echogenicity, and resistive index (RI). Laboratory parameters were serum creatinine level, urinary protein level, and serum markers of disease activity. Biopsy parameters were activity index, chronicity index, and assessment of the tubulointerstitium of the kidney. Follow-up data were obtained in all patients for at least 1 year. RESULTS: Ten patients with elevated RI (>0.70) had significantly (P <.05) higher chronicity indexes and creatinine levels than the 24 patients with a more normal RI. RI correlated significantly (P <.05) with creatinine level, chronicity index, and presence of interstitial disease. Only RI and chronicity index were statistically significant predictors of a poor renal outcome. Abnormalities at conventional US were not predictive of renal outcome. A normal RI predicted a better renal outcome whether or not creatinine level was elevated. CONCLUSION: Renal Doppler US may be of greatest clinical utility when its results are apparently discordant with renal functional assessment by allowing identification of patients with higher likelihood of subsequent improvement or worsening of renal status.

Doppler ultrasound of the kidney.

Conventional ultrasound of the kidney is used commonly to depict structural abnormalities. It is limited, however, by a lack of functional and vascular information. Doppler sonography can reduce this limitation of standard sonography quickly and noninvasively. Doppler examinations, although not difficult, must be done property to obtain useful data. Information regarding the presence and direction of flow in renal vessels can be obtained. Vascular stenosis can be identified by several Doppler criteria, although the role of Doppler as a screening measure remains controversial. Assessment of vascular resistance is possible from Doppler waveform analysis, using parameters such as the resistive index. These data may provide hemodynamic and predictive information regarding a dilated collecting system identified by conventional ultrasound. Analysis of the resistive index also may provide helpful clinical information in nonobstructive renal disease. In certain clinical settings, such analysis provides diagnostic data not readily available with other clinical and laboratory assessment methods. Pharmacologically stimulated renal Doppler examinations may lead to even greater benefits in the future. This article reviews renal Doppler ultrasound, including the physiological basis for Doppler examination, the technical principles of renal Doppler sonography, and the clinical applications of Doppler findings.

Use of Doppler sonography for revealing hepatic artery stenosis in liver transplant recipients.

OBJECTIVE: The goal of our study was to evaluate the use of duplex Doppler sonography for revealing hepatic artery stenosis (HAS) in patients who have undergone liver transplantation. MATERIALS AND METHODS: Forty-six patients with spectral Doppler waveforms obtained from the hepatic artery and with subsequent arteriography were reviewed retrospectively. Arterial waveforms, resistive indexes (RIs), and systolic acceleration times (SATs) were evaluated by one reviewer who was unaware of the arteriographic findings. The mean interval between the two examinations was 2.8 days. Arteriograms that revealed a stenosis of greater than 50% were classified as abnormal. RESULTS: Of the 46 patients, 21 (46%) had a significant stenosis. Patients who had HAS had significantly (p < .05) prolonged SATs (0.08 +/- 0.03 sec versus 0.06 +/- 0.02 sec) and reduced RIs (0.49 +/- 0.05 versus 0.66 +/- 0.05) compared with patients who did not have HAS. Optimal thresholds for HAS detection were RIs less than 0.55 and SATs greater than 0.08 sec. HAS was found in 14 of 15 patients who had both abnormal RIs and SATs. Of the remaining 31 patients, 12 had abnormal values for RI or SAT. Of these 12 patients, three had HAS. Thus, 19 patients had normal RIs and SATs; however, four of these patients were found to have an arterial stenosis. In our 46 patients, abnormal values for both RI and SAT were 67% sensitive and 96% specific for stenosis. When at least one abnormal value was found on Doppler imaging, sensitivity and specificity for stenosis were 81% and 60%, respectively. CONCLUSION: Duplex Doppler imaging can noninvasively reveal HAS. Abnormal values for both RI and SAT proved to be a more accurate predictor of stenosis than either RI or SAT as independent parameters.

Renal transplant evaluation with power Doppler sonography.

This study was performed to determine if the marked variation we had previously noted in the power Doppler sonographic appearance of renal transplants correlated with disease, 22 renal transplants were scanned with power Doppler at 5 MHz, with biopsies being taken within 1 h in 17 kidneys and within 48 h in four other kidneys. Biopsy was not performed in one kidney with distal ureteral obstruction. Biopsy results were complex with many coexistent abnormalities; classification was based upon the predominant abnormality. Cortical vascularity was subjectively evaluated as normal, decreased or markedly decreased, and graded as 0, 1 or 2, respectively, and was compared with biopsy results, serum creatinine levels and resistive index. Cortical vascularity gradings were: 0 (12 cases); 1 (7 cases); and 2 (3 cases). The large number of disease categories (cellular rejection, 11 cases; vascular rejection, 5 cases; IgA nephropathy, 1 case; cyclosporin toxicity, 3 cases; obstruction, 1 case; and lupus nephropathy, 1 case) in relation to the number of vascular grades and number of kidneys precluded statistical analysis of cortical vascularity for rejection. However, vascularity did not appear to correlate with rejection, the three severest cases of vascular rejection having normal (grade 0) vascularity. There was no statistically significant correlation of vascular grade with creatinine levels or resistive index. In conclusion, subjective analysis of the power Doppler sonographic appearance of renal transplants does not appear to aid in their evaluation.

Urinary obstruction.

Radiologic imaging is commonly used in the diagnosis, classification, and follow-up of renal obstruction. Precise definitions of the elements of urinary obstruction are critical. This article examines the physiology of renal obstruction and the use of such imaging tests as excretory urogram, retrograde pyelography, antegrade pyelography, Whitaker test, ultrasound, CT scan, MR imaging, and radionuclide renography.

Tumorous intrahepatic lymphoproliferative disorder in transplanted livers.

OBJECTIVE: We describe the radiologic findings of lymphoproliferative disorder manifesting as an intrahepatic mass in hepatic transplant recipients. Three patients with focal intrahepatic masses due to lymphoproliferative disorder after transplantation were retrospectively identified. Clinical features and radiologic findings in these patients were reviewed in conjunction with pertinent cases from the literature. (Reports of lymphoproliferative disorder confined to the transplanted liver have been sporadic.) CONCLUSION: Factors supporting the diagnosis of tumorous intrahepatic lymphoproliferative disorder include presentation 4-12 months after transplantation; portal or periportal location; poorly defined extrahepatic periportal soft tissue; encasement or narrowing of the biliary ducts, hepatic artery, or portal vein; and serologic evidence of exposure to Epstein-Barr virus.

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.

Hepatic hemodynamic alterations after administration of oral CT contrast agents.

PURPOSE: To assess the effects of oral computed tomography (CT) contrast agents on hepatic hemodynamics with duplex Doppler ultrasound (US). MATERIALS AND METHODS: Thirty healthy subjects who fasted underwent duplex Doppler US of the hepatic artery and portal vein both before and after administration of oral CT contrast agents. Resistive indexes were determined for the hepatic arteries. Peak and mean velocity (centimeters per second) and mean diameter were calculated for the main portal vein. RESULTS: Statistically significant elevation of the resistive index (P < .01) of the hepatic arteries was observed after ingestion of oral CT contrast agents. Increase in the mean resistive index at 15 minutes was 12% in the proper hepatic arteries and 20% in the intrahepatic arteries. There was a postprandial increase in mean portal venous flow compared with baseline levels (1,110 mL/min +/- 210 vs 940 mL/min +/- 140) (P < .05). CONCLUSION: An elevation of hepatic artery resistance that is probably due to arterial vasoconstriction after ingestion of oral CT contrast agents can be observed with Doppler US. Hemodynamic changes in liver vasculature after ingestion of oral CT contrast agents may have as yet unknown implications for CT scanning of the liver.