Cine viewing of abdominal CT

Characterization and identification of spatial artifacts during 4D-CT imaging

PURPOSE

The purpose of this work is twofold: First, to characterize the artifacts occurring in helical 4D-CT imaging; second, to propose a method that can automatically identify the artifacts in 4D-CT images. The authors have designed a process that can automatically identify the artifacts in 4D-CT images, which may be invaluable in quantifying the quality of 4D-CT images and reducing the artifacts from the reconstructed images on a large dataset.

METHODS

Given two adjacent stacks obtained from the same respiration phase, the authors determine if there are artifacts between them. The proposed method uses a "bridge" stack strategy to connect the two stacks. Using normalized cross correlation convolution (NCCC), the two stacks are mapped to the bridge stack and the best matching positions can be located. Using this position information, the authors can then determine if there are artifacts between the two stacks. By combining the matching positions with NCCC values, the performance can be improved.

RESULTS

To validate the method, three expert observers independently labeled over 600 stacks on five patients. The results confirmed that high performance was obtained using the proposed method. The average sensitivity was about 0.87 and the average specificity was 0.82. The proposed method also outperformed the method of using respiratory signal (sensitivity increased from 0.50 to 0.87 and specificity increased from 0.70 to 0.82).

CONCLUSIONS

This study shows that the spatial artifacts during 4D-CT imaging are characterized and can be located automatically by the proposed method. The method is relatively simple but effective. It provides a way to evaluate the artifacts more objectively and accurately. The reported approach has promising potential for automatically identifying the types and frequency of artifacts on large scale 4D-CT image dataset.

Metastases of colorectal carcinoma: comparison of soft- and hard-copy helical CT interpretation

PURPOSE

To compare soft- and hard-copy computed tomographic (CT) image interpretation with regard to evaluation time and detection rates for hepatic and extrahepatic colorectal metastases in candidates for liver surgery.

MATERIALS AND METHODS

In 20 patients with a history of colorectal carcinoma, two radiologists independently evaluated CT data sets. Focal hepatic lesions were characterized as benign or malignant by using a five-point scale. In each patient, soft-copy readouts and hard-copy printouts were compared for nonenhanced hepatic, contrast material-enhanced hepatic, and contrast-enhanced extrahepatic data sets. A stopwatch was used to document evaluation time. Ninety-two hepatic metastases and six extrahepatic metastatic recurrences were detected with the standard of reference--surgical, intraoperative ultrasonographic, and histologic findings.

RESULTS

Both observers evaluated the contrast-enhanced hepatic data set significantly faster (P =.026 and.009) by using soft-copy readouts. The contrast-enhanced extrahepatic data set was also evaluated significantly faster (P =.010 and.006) with soft-copy readouts. Detection of hepatic and extrahepatic tumor with soft-copy readouts is not significantly superior to that with hard copies. Detection rates of hepatic metastases for nonenhanced and contrast-enhanced CT for both observers ranged from 50%-80% (46-74 of 92) for soft-copy readouts and 46%-75% (42-69 of 92) for hard copies. Interobserver agreement was highest for contrast-enhanced soft-copy readouts for hepatic metastases.

CONCLUSION

Soft-copy readouts of contrast-enhanced CT data sets for the detection of hepatic metastases and extrahepatic metastatic recurrences were evaluated significantly faster than were hard copies, with at least equal sensitivity and with excellent interobserver agreement.