Spiral CT of the abdomen: region coverage with a 24-second breath-hold

Influence of visual distractors on detectability of liver nodules on contrast-enhanced spiral computed tomography scans

RATIONALE AND OBJECTIVES

The authors evaluated the ability of observers to identify simulated nodules placed electronically on normal contrast material-enhanced computed tomography (CT) scans of the liver to assess the effect of nodule size and polarity on detection and localization.

METHODS

Seven readers evaluated two sets of CT scans that contained 80 stimuli each. The simulated nodules were either darker or brighter than the contrast-enhanced liver and were 5.6-8.0 mm in diameter. Readers were asked to find the most suspicious-looking nodule on each section and rate the likelihood that the chosen location actually contained a nodule.

RESULTS

The fraction of nodules found by each observer was substantially greater for dark nodules than for bright ones (0.679 +/- 0.03 vs 0.345 +/- 0.045, respectively [mean +/- standard error]). This difference was consistent for all nodule sizes. Additional analyses (including receiver operating characteristic curves of conditional responses) suggested that the presence of bright blood vessels distracted the readers and decreased their ability to find bright nodules.

CONCLUSION

Normal vascular structures on contrast-enhanced CT scans of the liver impair an observer's ability to detect bright liver nodules.

Spiral CT for the detection of hepatocellular carcinomas:relative value of arterial- and late-phase scanning

BACKGROUND

Spiral computed tomography (CT) can image the liver during arterial and late phases of contrast and optimize the evaluation of hypervascular tumor. The objective of this study was to evaluate the relative value of arterial- and late-phase spiral CT in the detection of hepatocellular carcinomas.

METHODS

Fifty-eight patients with hepatocellular carcinomas underwent two-phase spiral CT examination with 10-mm collimation at 10 mm/s table speed (Siemens Somatom Plus S), and 120 mL of contrast material (36 g iodine) was injected at the rate of 3 mL/s. CT images of hepatic arterial and late phases were obtained with a 35-s and 180-s delay, respectively.

RESULTS

In 58 patients, 111 hepatocellular carcinoma lesions were seen. The arterial phase detected 93 (84%) and the late phase 75 (68%) lesions (p < 0.01). The arterial phase detected more lesions in 11 patients, and the late phase detected more in two patients and an equal number in 45 patients. If lesions larger than 2 cm are excluded, the arterial phase detected 40 (74%) and the late phase 21 (39%) of 54 lesions (p < 0.001).

CONCLUSION

The arterial phase of spiral CT greatly improves the detection of hepatocellular carcinoma when compared with the late phase.

Characterization of focal hepatic tumors. Value of two-phase scanning with spiral computed tomography

BACKGROUND

Spiral computed tomography (CT) allows imaging of the liver during the peak contrast material levels due to the capability of fast data acquisition. The objective of this study was to evaluate the usefulness of two-phase spiral CT in the differential diagnosis of focal hepatic tumors.

METHODS

One hundred two patients who had hepatic tumors (211 nodules; 149 hepatocellular carcinomas [HCCs], 36 metastases, and 26 hemangiomas) underwent two-phase spiral CT with 10-mm collimation at 10 mm/second table speed and 120 mL of contrast material injected at the rate of 3 mL/second. Computed tomography images of the hepatic arterial phase and late (equilibrium) phase were obtained at 35-second and 180-second delays, respectively. The enhancement patterns of tumors were divided into six types and were compared with the attenuation of surrounding liver parenchyma: totally high, peripherally high, centrally high, mixed, iso, and low.

RESULTS

The common enhancement patterns of HCC in two-phase spiral CT were totally high in the arterial phase and low (n = 63, 42%) or iso (n = 28, 19%) in the late phase. Metastasis showed peripherally nonnodular high attenuation (n = 9, 25%) or low attenuation (n = 9, 25%) in the arterial phase and low attenuation in the late phase, followed by totally high attenuation in the arterial phase and iso in the late phase (n = 6, 17%). Hemangiomas showed totally or peripherally nodular enhancement in the arterial and late phases (n = 23, 89%). In distinguishing hemangiomas from malignant tumors, totally high or peripherally nodular high attenuation in the late phase was the most useful contrast enhancement pattern (96% of hemangioma vs. 0% of malignant tumors). In distinguishing HCCs from metastases, a combination of contrast enhancement pattern of totally high attenuation in the arterial phase and low in the late phase was the most useful contrast enhancement pattern (42% of HCCs vs. 0% of metastases). The predictability of differentiation between hemangiomas and malignant tumors and between HCCs and metastases was 99% and 90% with spiral CT, respectively.

CONCLUSIONS

Two-phase spiral CT is useful in the differential diagnosis of focal hepatic tumors with evaluation of contrast enhancement patterns.