Quantification of hepatic steatosis with T1-independent, T2-corrected MR imaging with spectral modeling of fat: blinded comparison with MR spectroscopy

PURPOSE

To prospectively compare an investigational version of a complex-based chemical shift-based fat fraction magnetic resonance (MR) imaging method with MR spectroscopy for the quantification of hepatic steatosis.

MATERIALS AND METHODS

This study was approved by the institutional review board and was HIPAA compliant. Written informed consent was obtained before all studies. Fifty-five patients (31 women, 24 men; age range, 24-71 years) were prospectively imaged at 1.5 T with quantitative MR imaging and single-voxel MR spectroscopy, each within a single breath hold. The effects of T2 correction, spectral modeling of fat, and magnitude fitting for eddy current correction on fat quantification with MR imaging were investigated by reconstructing fat fraction images from the same source data with different combinations of error correction. Single-voxel T2-corrected MR spectroscopy was used to measure fat fraction and served as the reference standard. All MR spectroscopy data were postprocessed at a separate institution by an MR physicist who was blinded to MR imaging results. Fat fractions measured with MR imaging and MR spectroscopy were compared statistically to determine the correlation (r(2)), and the slope and intercept as measures of agreement between MR imaging and MR spectroscopy fat fraction measurements, to determine whether MR imaging can help quantify fat, and examine the importance of T2 correction, spectral modeling of fat, and eddy current correction. Two-sided t tests (significance level, P = .05) were used to determine whether estimated slopes and intercepts were significantly different from 1.0 and 0.0, respectively. Sensitivity and specificity for the classification of clinically significant steatosis were evaluated.

RESULTS

Overall, there was excellent correlation between MR imaging and MR spectroscopy for all reconstruction combinations. However, agreement was only achieved when T2 correction, spectral modeling of fat, and magnitude fitting for eddy current correction were used (r(2) = 0.99; slope ± standard deviation = 1.00 ± 0.01, P = .77; intercept ± standard deviation = 0.2% ± 0.1, P = .19).

CONCLUSION

T1-independent chemical shift-based water-fat separation MR imaging methods can accurately quantify fat over the entire liver, by using MR spectroscopy as the reference standard, when T2 correction, spectral modeling of fat, and eddy current correction methods are used.

Metabolite quantification and high-field MRS in breast cancer

In vivo 1H MRS is rapidly developing as a clinical tool for diagnosing and characterizing breast cancers. Many in vivo and in vitro experiments have demonstrated that alterations in concentrations of choline-containing metabolites are associated with malignant transformation. In recent years, considerable efforts have been made to evaluate the role of 1H MRS measurements of total choline-containing compounds in the management of patients with breast cancer. Current technological developments, including the use of high-field MR scanners and quantitative spectroscopic analysis methods, promise to increase the sensitivity and accuracy of breast MRS. This article reviews the literature describing in vivo MRS in breast cancer, with an emphasis on the development of high-field MR scanning and quantitative methods. Potential applications of these technologies for diagnosing suspicious lesions and monitoring response to chemotherapy are discussed.

Adding in Vivo Quantitative1H MR Spectroscopy to Improve Diagnostic Accuracy of Breast MR Imaging: Preliminary Results of Observer Performance Study at 4.0 T

PURPOSE

To determine whether the addition of in vivo quantitative hydrogen 1 (1H) magnetic resonance (MR) spectroscopy can improve the radiologist's diagnostic accuracy in interpreting breast MR images to distinguish benign from malignant lesions.

MATERIALS AND METHODS

The study was approved by the institutional review board and, where appropriate, was compliant with the Health Insurance Portability and Accountability Act. All patients provided written informed consent. Fifty-five breast MR imaging cases-one lesion each in 55 patients aged 24-66 years with biopsy-confirmed findings-were retrospectively evaluated by four radiologists. Patients were examined with contrast material-enhanced fat-suppressed T1-weighted 4.0-T MR imaging. The concentration of total choline-containing compounds (tCho) was quantified by using single-voxel 1H MR spectroscopy. For each case, the radiologists were asked to give the percentage probability of malignancy, the Breast Imaging and Reporting Data System category, and a recommendation for patient treatment. Two interpretations were performed for each case: The initial interpretation was based on the lesion's morphologic features and time-signal intensity curve, and the second interpretation was based on the lesion's morphologic features, time-signal intensity curve, and tCho concentration. Receiver operating characteristic (ROC), Wilcoxon signed rank, kappa statistic, and accuracy (based on the area under the ROC curve) analyses were performed.

RESULTS

Of the 55 lesions evaluated, 35 were invasive carcinomas and 20 were benign. The addition of 1H MR spectroscopy resulted in higher sensitivity, specificity, accuracy, and interobserver agreement for all four radiologists. More specifically, two of the four radiologists achieved a significant improvement in sensitivity (P=.03, P=.03), and all four radiologists achieved a significant improvement in accuracy (P = .01, P = .05, P = .009, P < .001).

CONCLUSION

Current study results suggest that the addition of quantitative 1H MR spectroscopy to the breast MR imaging examination may help to improve the radiologist's ability to distinguish benign from malignant breast lesions.

Neoadjuvant chemotherapy of locally advanced breast cancer: predicting response with in vivo (1)H MR spectroscopy--a pilot study at 4 T

PURPOSE

To determine if changes in the concentration of choline-containing compounds (tCho) from before primary systemic therapy (PST) to within 24 hours after the first treatment enable prediction of clinical response in patients with locally advanced breast cancer.

MATERIALS AND METHODS

Sixteen women with biopsy-confirmed locally advanced breast cancer scheduled to undergo doxorubicin-based PST were recruited. Magnetic resonance (MR) imaging and spectroscopy were performed at 4 T prior to treatment, within 24 hours after the first dose, and after the fourth dose. Lesion size was assessed by using gadolinium-enhanced MR imaging. Lesion tCho concentration was quantified by using single-voxel hydrogen 1 MR spectroscopy. Statistical analysis was performed by using the Pearson correlation coefficient and the Wilcoxon rank sum test.

RESULTS

Fourteen of 16 patients completed the protocol. In one patient, the level of tCho was not measurable because of unfavorable lesion morphology for MR spectroscopy voxel placement. Of the remaining 13 patients, four had inflammatory breast cancer, six had invasive ductal carcinoma, two had invasive lobular carcinoma, and one had mixed invasive ductal and lobular carcinoma. On the basis of the Response Evaluation Criteria in Solid Tumors, eight of 13 patients had an objective response and five had no response. The change in concentration of tCho from baseline to within 24 hours after the first dose of PST showed significant positive correlation with the change in lesion size (R = 0.79, P = .001). Change in tCho concentration within 24 hours after first dose was significantly different between patients with objective response and those with no response (P = .007).

CONCLUSION

These results suggest that the change in tCho concentration between baseline and 24 hours after the first dose of PST can serve as an indicator for predicting clinical response to doxorubicin-based chemotherapy in locally advanced breast cancer.

Combined Transthoracic and Transtracheal Closure of Large Bronchopleural Fistulae

PURPOSE

Postoperative central bronchopleural fistulae (BPF) are difficult to close using percutaneous or endoscopic techniques. We devised an alternative method to treat BPF using a combined transthoracic and transtracheal approach with the use of a multifilamented polypropylene (Prolene) mesh patch.

METHODS

Two patients with large, central BPF after thoracic surgery and lobar resection had minimally invasive BPF closure using a transtracheal approach with catheterization of the fistula and thoracoscopically guided Prolene mesh placement over the bronchial stump defect. This technique was adopted after conservative management and multiple endobronchial interventions had failed in both patients.

RESULTS

One patient had closure of his BPF within one week and remains symptom-free one year after chest tube removal. The other patient had a BPF and chest tube for two years prior to our procedure. His BPF initially closed, but recannalized 2 weeks later. He subsequently had two thoracotomies and continues to suffer a BPF which remains externalized to his chest wall.

CONCLUSIONS

Post-thoracotomy central BPF that is resistant to nonsurgical treatments can be closed with a combined thoracoscopic and transtracheal placement of a polypropylene patch. The success of this repair seems to depend on early intervention and aggressive sterilization of the pleural space.

Measurement and correction of respiration-inducedB0 variations in breast1H MRS at 4 Tesla

Respiratory motion is well known to cause artifacts in magnetic resonance spectroscopy (MRS). In MRS of the breast, the dominant artifact is not due to motion of the breast itself, but rather it is produced by B0 field distortions associated with respiratory motion of tissues in the chest and abdomen. This susceptibility artifact has been reported to occur in the brain, but it is more apparent in the breast due to the anatomic proximity of the lungs. In the breast, these B0 distortions cause shot-to-shot frequency shifts, which vary an average of 24 Hz during a typical 1H MRS scan at 4 T. This variation can be corrected retrospectively by frequency shifting individual spectra prior to averaging. If not corrected, these shifts reduce spectral resolution and increase peak fitting errors. This work demonstrates the artifact, describes a method for correcting it, and evaluates its impact on quantitative spectroscopy. When the artifact is not corrected, quantification errors increase by an average of 28%, which dramatically impacts the ability to measure metabolite resonances at low signal-to-noise ratios.

In vivo quantification of choline compounds in the breast with1H MR spectroscopy

This work describes a methodology for quantifying levels of total choline-containing compounds (tCho) in the breast using in vivo (1)H MR spectroscopy (MRS) at high field (4 Tesla). Water is used as an internal reference compound to account for the partial volume of adipose tissue. Peak amplitudes are estimated by fitting one peak at a time over a narrow frequency band to allow measurement of small metabolite resonances in spectra with large lipid peaks. This quantitative method significantly improves previously reported analysis methods by accounting for the variable sensitivity of breast (1)H MRS measurements. Using this technique, we detected and quantified a tCho peak in 214 of 500 in vivo spectra. tCho levels were found to be significantly higher in malignancies than in benign abnormalities and normal breast tissues, which suggests that this technique could be used to diagnose suspicious lesions and monitor response to cancer treatments.