Purpose: Most hepatic metastases are hypovascular, and CT scanning during peak hepatic enhancement is thusimportant for the detection of hepatic lesions. The purpose of this study was to determine whether images obtainedby bolus tracking show greater hepatic enhancement. Materials and Methods: We prospectively evaluated 101 patientswho underwent helical CT of the abdomen, using either a fixed 60-sec delay(n=50) or bolus tracking (n=51). For thelatter, we used a hepatic enhancement threshold of 50HU over baseline on monitor phase to determine a 6-sec delaybetween the monitor and diagnostic scanning phase. For all patients, three region-of-interest measurements wererecorded, one at each of the upper, middle, and lower levels of the liver; the measurements were averaged andsubtracted from the baseline density that measured CT values in three different hepatic segments at the mid-levelof the liver. We compared mean enhancement above the baseline of the liver between fixed 60-sec delay and bolustracking. Results: A statistically significant difference in the enhancement level of the liver (upper, p=.001;middle, p=.001; lower, p=.003) was noted between fixed 60-sec delay (upper, 65.3$pm$16HU; middle, 67.4$pm$16.5HU;lower, 68.5(19.4HU) and bolus tracking (upper, 75.2$pm$15.5HU; middle, 74.4$pm$13.7HU;lower, 75.6$pm$13.6HU). With fixeddelay, 86% of patients reached 50HU of enhancement, but with bolus tracking, 98% reached this level. For onenhancement value of 60HU, the corresponding figures were 64% and 86%. Mean delay for the transition betweenmonitoring scans and diagnostic scan initiation was 63.8$pm$7.9(range, 48-79)secs. For two patients in whom theenhancement curve did not reach threshold (50HU), the default time was 70 sec; one subsequently failed to reachthis same threshold. Conclusion: Using the same amounts of contrast material, bolus tracking provides a greaterlevel of hepatic enhancement than a fixed 60-ses delay, and is thus helpful for the detection of hypovascularmasses such as metastatic lesions. renal medulla were obtained from ten healthy rabbits. Each tissue sample was placed in 75% ethanol, 10%formalin, and 0.9% normal saline and MR scans of each sample were performed at 30 minutes, 11/2, 3, 6, and 12hours after resection. Signal intensities of the images were measured and their sequential changes were evaluated.Results: On T1WI, signal intensities of both tissue specimens fixed in formalin and ethanol and untreatedspecimens increased significantly during the first 30 minutes. The increased signal intensity then seen for 12hours was greater than on T2WI. On T2WI, signal ntensities of tissue specimens fixed in formalin and ethanol anduntreated specimens showed no significant changes within the first 30 minutes; after that, they showed less signalintensity change for 12 hours than on T1WI. Conclusion: To obtain MR images with the same signal intensities as invivo tissue, MRI of tissue specimens in the untreated state should be performed as soon as possible afterresection. On T2WI, signal intensities of tissue specimens were more similar to in vivo tissue than on T1WI.