Detection of focal hepatic masses: STIR MR vs. CT during arterial portography

Radiological staging of colorectal liver metastases

Rapid advances in imaging technology have improved the detection, characterization and staging of colorectal liver metastases. Multi-modality imaging approach is usually the more useful in staging colorectal liver metastases. Multi-detector computed tomography (MDCT) remains the main imaging modality for preoperative planning, lesion detection and tumour surveillance. Magnetic resonance imaging (MRI) and contrast enhanced ultrasonography (US) are invaluable in problem solving for characterization indeterminate lesions, while contrast enhanced intra-operative ultrasound (CE-IOUS) may be the new gold standard staging tool prior to liver resection. Ultimately, the imaging strategy has to be tailored to the clinical situation to obtain the most relevant information for optimal use of available imaging resources.

Prospective study of contrast-enhanced computed tomography, computed tomography during arterioportography, and magnetic resonance imaging for staging colorectal liver metastases for liver resection

BACKGROUND

This study compared the value of contrast-enhanced helical computed tomography (CT), CT during arterioportography (CTAP), and contrast-enhanced magnetic resonance imaging (MRI) for staging patients with colorectal liver metastases.

METHODS

One hundred and twenty patients with known or suspected colorectal liver metastases were evaluated prospectively. MRI and CTAP were performed within 3 weeks of CT in patients with potentially resectable tumours. Results of imaging were compared with findings at surgery, intraoperative ultrasonography and histological examination.

RESULTS

Twenty patients were not considered for liver resection following CT. The remaining 100 patients underwent CT and CTAP, 85 of whom had CT, CTAP and MRI. The sensitivity and specificity were 73.0 and 96.5 per cent for CT, 87.1 and 89.3 per cent for CTAP, and 81.9 and 93.2 per cent for MRI. Positive predictive values were 89.7, 87.5 and 87.5 per cent respectively. Receiver-operator characteristic analysis gave an accuracy on a segment-by-segment analysis of 0.73 for CT, 0.87 for CTAP and 0.82 for MRI. Combining information from CT and CTAP, CT and MRI, or all three modalities, did not significantly increase the percentage of patients staged correctly (71, 72 and 76 per cent respectively).

CONCLUSION

The diagnostic accuracy of spiral CT, MRI and CTAP was similar. Combining modalities did not improve accuracy.

Imaging the fatty liver

Even though various imaging techniques are available to detect fat, chemical-shift imaging is the most accurate for both qualitative and quantitative measurement of fat. It can be very useful in liver studies, not only because it definitively demonstrates fatty liver but also because it improves lesion detection and characterization in some cases.

Detection of focal hepatic lesions: comparison of unenhanced and SHU 555 A-enhanced MR imaging versus biphasic helical CTAP

The purpose of this study was to compare the diagnostic sensitivity of unenhanced magnetic resonance (MR) imaging, and MR imaging with a new superparamagnetic iron oxide (SPIO)-enhanced contrast agent (SHU 555 A) with biphasic helical computed tomography during arterial portography (CTAP) in patients with focal liver lesions. Eighteen patients with a total of 91 (78 malignant, 13 benign) proven liver lesions underwent unenhanced short tau inversion recovery (STIR), T2-weighted (T2-w) TSE, and SHU 555 A-enhanced T2-w turbo spin-echo (TSE) MR imaging and biphasic helical CTAP. The standard of reference was histopathologic analysis of resected specimens in 59 lesions, intraoperative ultrasound with biopsy in 20 lesions, and CT-guided biopsy and follow-up in 12 lesions. Diagnostic performance of the imaging modalities was compared quantitatively and qualitatively by assessing lesion involvement in liver segments. There were 68 lesions detected on unenhanced T2-w TSE, which resulted in a sensitivity of 75%. With the STIR sequence, 76 lesions were detected, for a sensitivity of 84%, and with SHU 555 A-enhanced MRI, 84 lesions were detected, for a sensitivity of 92%. CTAP detected 88 lesions, for a sensitivity of 97%. The accuracy for unenhanced T2-w TSE was 98%, for STIR 99%, for enhanced-MRI 100%, and for CTAP 95%. The specificity was 100% for SHU 555 A-enhanced MRI and 95% for CTAP. SHU 555 A-enhanced MRI was superior to nonenhanced MRI (P < 0.05) and equivalent to CTAP in terms of sensitivity. Due to the absence of false-positive results on SHU 555 A-enhanced MRI, the specificity and accuracy of enhanced MRI were higher than those of CTAP, but the difference was not statistically significant (P = 0.134).

A prospective assessment of breath-hold fast spin echo and inversion recovery fast spin echo techniques for detection and characterization of focal hepatic lesions

The purpose of this study was to prospectively assess two breath-hold T(2)-weighted fast spin-echo sequences and two breath-hold inversion recovery fast spin-echo sequences to determine their relative ability to detect and characterize focal hepatic lesions. Fourteen patients with a total of nineteen proven focal hepatic lesions were imaged with two breath-hold T(2)-weighted (T2W) fast spin echo sequences (HASTE TE = 66 and HASTE TE = 120), two breath-hold inversion recovery fast spin echo sequences (IRFSE TE = 64 and IRFSE TE = 95), and a nonbreath-hold T(2)-weighted fast-spin echo sequence (FSE TE = 96-120). Contrast-to-noise ratios (CNRs) were measured for all proven lesions on all sequences. Both IRFSE sequences and the HASTE sequence with TE = 66 showed an improvement in lesion-liver and liver-spleen CNRs compared to the nonbreath-hold T2W sequence. The mean difference in CNR between benign and malignant lesions was largest for the HASTE TE = 120 sequence. These preliminary results suggest that a breath-hold IRFSE sequence (TE = 64 or 95) has an equal ability to detect focal hepatic lesions as a nonbreath-hold T2W FSE sequence (TE = 96-120). The HASTE TE = 120 showed the greatest ability to discriminate between benign and malignant lesions.

MR imaging techniques of the liver

This article reviews the currently available MR imaging techniques that are useful for the detection and characterization of focal and diffuse liver pathology. The implementation and clinical utility of various T1-weighted, T2-weighted, T2*-weighted, and MR angiographic sequences are described.

Optimizing fast spin echo acquisitions for hepatic imaging in normal subjects

The purpose of this study was to determine which implementations of a T2-weighted fast spin-echo sequence of the liver resulted in observer preference in normal subjects. Five volunteers were scanned with a series of fast spin-echo sequences modified to allow for flow compensation, respiratory triggering (RT), ECG triggering, randomized phase encoding (RPE), breath-holding, and echo train length (ETL). Images were compared with conventional 2500/40/80 msec spin-echo images using flow compensation and spatial presaturation by two observers blinded to the specific sequence parameters. All FSE sequences were completed in less than the 12 minutes necessary to perform a conventional spin-echo sequence. The most preferred fast spin-echo sequence employed flow compensation, RT, and used an 8 ETL. Analysis of image preference, signal to noise, and contrast to noise showed that RT was the single most important variable in determining each image response (P < .01, P < .02, P < .01, respectively). There was some evidence that images obtained with an 8 ETL were preferred over those using a 16 ETL (P = .07). No other variables approached statistical significance although one reader preferred images with flow compensation in the frequency direction to those either not flow compensated or flow compensated in the slice direction. Respiratory triggered fast spin-echo images combined with flow compensation in the frequency direction and using ETL = 8 can provide image quality equal to conventional spin-echo sequences with significant time savings.

Malignant liver lesions: comparison of spiral CT arterial portography and MR imaging for diagnostic accuracy, cost, and effect on patient management

We compared two imaging techniques, spiral CT arterial portography (CTAP) and MR imaging, for diagnostic accuracy, procedural cost, and effect on management of 26 patients referred for hepatic surgery for suspected limited malignant liver disease. CTAP and MR imaging were done within a 1-week period (19 within 24 hours); the results of the studies were interpreted prospectively by separate reviewers. Surgical data were evaluated in conjunction with imaging data in 10 patients. Lesion detection and segmental involvement were determined and sensitivity and specificity were calculated. Procedural cost was determined from hospital billing codes. Effect on patient management was determined by the referring oncologic surgeon. CTAP and MR imaging showed 185 and 176 true-positive malignant lesions, 15 and zero false-positive malignant lesions, zero and 18 true-negative malignant lesions, and 13 and 22 false-negative malignant lesions, respectively. CTAP and MR imaging showed 107 and 105 true-positive segments, 11 and zero false-positive segments, 80 and 91 true-negative segments, and four and six false-negative segments, respectively. There was a significant difference in specificity of segmental involvement between MR imaging (1.0 +/- 0) compared with CTAP (0.88 +/- 0.05), P = .03. Total procedural cost was $3,499 for CTAP and $1,224 for MR imaging. CTAP findings did not change patient management over MR imaging findings in any patient, whereas MR imaging findings resulted in a change in patient management over CTAP findings in seven patients (P = .015). The results of our study suggest that MR imaging has higher diagnostic accuracy and greater effect on patient management than CTAP does and is 64% less expensive.