A test of performance of breast MRI interpretation in a multicentre screening study

A Metric for Reducing False Positives in the Computer-Aided Detection of Breast Cancer from Dynamic Contrast-Enhanced Magnetic Resonance Imaging Based Screening Examinations of High-Risk Women

Magnetic resonance imaging (MRI)-enabled cancer screening has been shown to be a highly sensitive method for the early detection of breast cancer. Computer-aided detection systems have the potential to improve the screening process by standardizing radiologists to a high level of diagnostic accuracy. This retrospective study was approved by the institutional review board of Sunnybrook Health Sciences Centre. This study compares the performance of a proposed method for computer-aided detection (based on the second-order spatial derivative of the relative signal intensity) with the signal enhancement ratio (SER) on MRI-based breast screening examinations. Comparison is performed using receiver operating characteristic (ROC) curve analysis as well as free-response receiver operating characteristic (FROC) curve analysis. A modified computer-aided detection system combining the proposed approach with the SER method is also presented. The proposed method provides improvements in the rates of false positive markings over the SER method in the detection of breast cancer (as assessed by FROC analysis). The modified computer-aided detection system that incorporates both the proposed method and the SER method yields ROC results equal to that produced by SER while simultaneously providing improvements over the SER method in terms of false positives per noncancerous exam. The proposed method for identifying malignancies outperforms the SER method in terms of false positives on a challenging dataset containing many small lesions and may play a useful role in breast cancer screening by MRI as part of a computer-aided detection system.

Semi-automatic region-of-interest segmentation based computer-aided diagnosis of mass lesions from dynamic contrast-enhanced magnetic resonance imaging based breast cancer screening

Cancer screening with magnetic resonance imaging (MRI) is currently recommended for very high risk women. The high variability in the diagnostic accuracy of radiologists analyzing screening MRI examinations of the breast is due, at least in part, to the large amounts of data acquired. This has motivated substantial research towards the development of computer-aided diagnosis (CAD) systems for breast MRI which can assist in the diagnostic process by acting as a second reader of the examinations. This retrospective study was performed on 184 benign and 49 malignant lesions detected in a prospective MRI screening study of high risk women at Sunnybrook Health Sciences Centre. A method for performing semi-automatic lesion segmentation based on a supervised learning formulation was compared with the enhancement threshold based segmentation method in the context of a computer-aided diagnostic system. The results demonstrate that the proposed method can assist in providing increased separation between malignant and radiologically suspicious benign lesions. Separation between malignant and benign lesions based on margin measures improved from a receiver operating characteristic (ROC) curve area of 0.63 to 0.73 when the proposed segmentation method was compared with the enhancement threshold, representing a statistically significant improvement. Separation between malignant and benign lesions based on dynamic measures improved from a ROC curve area of 0.75 to 0.79 when the proposed segmentation method was compared to the enhancement threshold, also representing a statistically significant improvement. The proposed method has potential as a component of a computer-aided diagnostic system.

Semi-quantitative parameter analysis of DCE-MRI revisited: monte-carlo simulation, clinical comparisons, and clinical validation of measurement errors in patients with type 2 neurofibromatosis

PURPOSE

To compare semi-quantitative (SQ) and pharmacokinetic (PK) parameters for analysis of dynamic contrast enhanced MR data (DCE-MRI) and investigate error-propagation in SQ parameters.

METHODS

Clinical data was collected from five patients with type 2-neurofibromatosis (NF2) receiving anti-angiogenic therapy for rapidly growing vestibular schwannoma (VS). There were 7 VS and 5 meningiomas. Patients were scanned prior to therapy and at days 3 and 90 of treatment. Data was collected using a dual injection technique to permit direct comparison of SQ and PK parameters. Monte Carlo modeling was performed to assess potential measurement errors in SQ parameters in persistent, washout, and weakly enhancing tissues. The simulation predictions for five semi-quantitative parameters were tested using the clinical DCE-MRI data.

RESULTS

In VS, SQ parameters and Ktrans showed close correlation and demonstrated similar therapy induced reductions. In meningioma, only the denoised Signal Enhancement Ratio (Rse1/se2(DN)) showed a significant therapy induced reduction (p<0.05). Simulation demonstrated: 1) Precision of SQ metrics normalized to the pre-contrast-baseline values (MSErel and ∑MSErel) is improved by use of an averaged value from multiple baseline scans; 2) signal enhancement ratio Rmse1/mse2 shows considerable susceptibility to noise; 3) removal of outlier values to produce a new parameter, Rmse1/mse2(DN), improves precision and sensitivity to therapy induced changes. Direct comparison of in-vivo analysis with Monte Carlo simulation supported the simulation predicted error distributions of semi-quantitative metrics.

CONCLUSION

PK and SQ parameters showed similar sensitivity to anti-angiogenic therapy induced changes in VS. Modeling studies confirmed the benefits of averaging baseline signal from multiple images for normalized SQ metrics and demonstrated poor noise tolerance in the widely used signal enhancement ratio, which is corrected by removal of outlier values.

Impact of breast MR in non-screening Australian clinical practice: audit data from a single-reader single-centre site

AIM

The aim of this study was to evaluate the accuracy and clinical impact of single-reader breast MR (BMR) used as a clinical 'problem solving' tool.

METHODS

Observational, retrospective, ethics approved data collection for all BMR were from May 2006 to February 2009 (n=143). Cases were stratified into groups according to indication for referral. MR data included single-reader MR diagnosis and breast imaging reporting and data system category (per-patient basis), MR descriptors of lesions (breast imaging reporting and data system lexicon), lesion number and location. Composite reference standard was established from surgical histology, core histology, cytology, MR imaging follow-up, conventional imaging follow-up and clinical follow-up in that order of priority. Impact was qualitatively captured by estimating change in management as the result of BMR.

RESULTS

Eighty-two cases were included and 61 were excluded (41 insufficient follow-up times, three known benign mass for clarification, two worried well screening and 15 other reasons). There was no statistically significant difference in included and excluded patient profiles. Our largest group of referrals was of patients with suspicious or unhelpful conventional imaging. BMR identified five malignancies in that group but missed four. In our smaller group of patients with metastatic axillary lymph nodes, BMR identified the occult primary cancer in all five cases.

CONCLUSION

In this 'problem solving' patient population, breast MR shows greatest impact in patients with carcinoma metastases to axillary nodes, but primary not visible. In symptomatic women with unhelpful imaging or with suspicious imaging but no pre-MR diagnosis, MR identified 5/41 carcinomas, but missed 4/41.

A margin sharpness measurement for the diagnosis of breast cancer from magnetic resonance imaging examinations

RATIONALE AND OBJECTIVES

Cancer screening by magnetic resonance imaging (MRI) has been shown to be one of the most sensitive methods available for the early detection of breast cancer. There is high variability in the diagnostic accuracy of radiologists analyzing the large amounts of data acquired in a breast MRI examination, and this has motivated substantial research toward the development of computer-aided detection and diagnosis systems. Most computer-aided diagnosis systems for breast MRI focus on dynamic information (how a lesion's brightness changes over the course of an examination after the injection of a contrast agent). The inclusion of lesion margin measurements is much less common. One characteristic of malignant tumors is that they grow into neighboring tissues. This growth creates tumor margins that are variably fuzzy or diffuse (ie, they are not sharp).

MATERIALS AND METHODS

In this short report, the authors present a new method for measuring a tumor's margin from breast MRI examinations and compare it with an existing mathematical technique for margin measurements.

RESULTS

The proposed method can yield a test with sensitivity of 77% (specificity, 65%) on screening data, outperforming existing mathematical lesion margin measurement methods. Furthermore, when the presented margin measurement is combined with existing dynamic features, there is a statistically significant improvement in computer-aided diagnosis test performance (P < .0014).

CONCLUSIONS

The proposed method for measuring a tumor's margin outperforms existing mathematical methods on an extremely challenging data set containing many small lesions. The technique presented may be useful in discriminating between malignant and benign lesions in the context of the computer-aided diagnosis of breast cancer from MRI.

Psychological impact and acceptability of magnetic resonance imaging and X-ray mammography: the MARIBS Study

Background:

As part of the Magnetic Resonance Imaging for Breast Screening (MARIBS), Study women with a family history of breast cancer were assessed psychologically to determine the relative psychological impact and acceptability of annual screening using magnetic resonance imaging (MRI) and conventional X-ray mammography (XRM).

Methods:

Women were assessed psychologically at baseline (4 weeks before MRI and XRM), immediately before, and immediately after, both MRI and XRM, and at follow-up (6 weeks after the scans).

Results:

Overall, both procedures were found to be acceptable with high levels of satisfaction (MRI, 96.3% and XRM, 97.7% NS) and low levels of psychological morbidity throughout, particularly at 6-week follow-up. Low levels of self-reported distress were reported for both procedures (MRI, 13.5% and XRM, 7.8%), although MRI was more distressing (P=0.005). Similarly, higher anticipatory anxiety was reported before MRI than before XRM (P=0.003). Relative to XRM, MRI-related distress was more likely to persist at 6 weeks after the scans in the form of intrusive MRI-related thoughts (P=0.006) and total MRI-related distress (P=0.014). More women stated that they intended to return for XRM (96.3%) than for MRI (88% P<0.0005). These effects were most marked for the first year of screening, although they were also statistically significant in subsequent years.

Conclusion:

Given the proven benefits of MRI in screening for breast cancer in this population, these data point to the urgent need to provide timely information and support to women undergoing MRI.

MRI features of intraductal papilloma of the breast: sheep in wolf's clothing?

BACKGROUND

Intraductal papillomas often present as small, smooth masses, dilated ducts or microcalcifications at mammography and as smooth, hypoechoic masses at sonography. At magnetic resonance imaging (MRI), intraductal papillomas often present as small smooth masses, however, often with strong enhancement with type 2 or 3 time intensity curves. The result of the MR analysis is therefore not infrequently inconclusive in order to characterize the mass as benign or malignant.

PURPOSE

To characterize the appearance of intraductal papillomas of the breast at MRI, and determine whether the application of diagnostic rules described in literature could contribute to correctly classifying the lesions as benign.

MATERIAL AND METHODS

Twenty patients with histologically proven intraductal papillomas were included. Two radiologists independently reviewed the MR images of the breast. The BI-RADS(®) nomenclature was used to describe morphology and contrast-enhancement kinetics. Interobserver agreement in the interpretation of the MR images by the two investigators was performed. Kappa coefficient was calculated as index for the level of agreement. Subsequently, three sets of diagnostic rules, including the Göttinger score described by Fischer and the interpretation flowcharts according to Kinkel and to Tozaki were applied to characterize whether a biopsy should be recommended or not.

RESULTS

All papillomas presented as masses on dynamic contrast-enhanced MRI. Only five papillomas showed a round, oval, or lobulated shape combined with smooth margins and continuous rise of the time intensity curve. Using the Göttingen score, biopsy would be recommended in 16 patients. Based on the interpretation flowcharts of Kinkel and of Tozaki, an additional 13 and 10 papillomas, respectively, were correctly classified as benign. Dilated ducts were visible in 10 patients. The interobserver agreement was good or excellent for all included variables.

CONCLUSION

Including systematic analysis of breast MRI to the diagnostic protocol and interpreting the images according to predetermined diagnostic rules, most solitary intraductal papillomas of the breast may be correctly characterized as benign.

Relating dose of contrast media administered to uptake and washout of malignant lesions on DCEMRI of the breast

RATIONALE AND OBJECTIVES

To quantify the relationship between dose of contrast administered and contrast kinetics of malignant breast lesions.

MATERIALS AND METHODS

A total of 108 patients with 120 malignant lesions were selected for an institutional review board-approved review. Dynamic magnetic resonance protocol: one pre- and three or five post-contrast (at a fixed volume of 20 mL of 0.5 M gadodiamide) images. Patients were stratified into groups based on dose of contrast administered, after calculation of body weight (kg): Dose Group 1, <0.122 mmol/kg; Dose Group 2, 0.123-0.155 mmol/kg; Dose Group, 3 > 0.155 mmol/kg. Analysis of kinetic curve shape was made according to the Breast Imaging Reporting and Data System lexicon. Several quantitative parameters were calculated including initial and peak enhancement percentage (E(1) and E(peak)). Linear regression was used to model the variation of kinetic parameters with dose.

RESULTS

There was no difference found in the qualitative Breast Imaging Reporting and Data System descriptors of curve shape between the three dose groups. There was a trend for E(1) and E(peak) to increase from Dose Group 1 to Dose Group 3 in malignant lesions overall, as well as in invasive ductal carcinoma lesions separately. Each decrement/increment of 0.05 mmol/kg in dose yielded a decrease/increase of 78% and 97% in E(1) for in situ and invasive cancers, respectively.

CONCLUSION

Contrast should be administered at fixed dose to achieve comparable levels of lesion uptake in women of different weights. Our results suggest that reducing the contrast administered to 0.05 mmol/kg, as has been suggested for patients at risk of developing nephrogenic systemic fibrosis, could substantially decrease the observed initial enhancement in some cancers.

Effect of the enhancement threshold on the computer-aided detection of breast cancer using MRI

RATIONALE AND OBJECTIVES

To evaluate the effect that variations in the enhancement threshold have on the diagnostic accuracy of two computer-aided detection (CAD) systems for magnetic resonance based breast cancer screening.

MATERIALS AND METHODS

Informed consent was obtained from all patients participating in cancer screening and this study was approved by the participating institution's review board. This retrospective study was nested in a prospective, single-institution, high-risk, breast screening study involving dynamic contrast-enhanced magnetic resonance imaging. Only those screening examinations (n = 223) for which a histopathological diagnosis was available were included. Two CAD methods were performed: the signal enhancement ratio (SER) and support vector machines (SVMs). Statistical analysis was performed by tracking changes in each CAD test's diagnostic accuracy (eg, receiver-operating characteristic [ROC] curve area, maximum possible sensitivity) with changes in the enhancement threshold.

RESULTS

The enhancement threshold plays a significant role in affecting a CAD test's potential sensitivity, ROC curve area, and number of assumed true and false-positive predictions per cancerous examination. A high threshold can also limit the CAD-based detection of the full size of a lesion.

CONCLUSIONS

Enhancement thresholds can limit a CAD test's ability to diagnose a lesion's full size and as such should not be raised above 60%. The clinically used SER method exhibits a high rate of false positives at low enhancement thresholds and as such the threshold should not be set lower than 50%. The SVM method yielded better results in our study than the SER method at clinically realistic enhancement thresholds.

The utility of MRI for the screening and staging of breast cancer

INTRODUCTION & BACKGROUND

Contrast-enhanced magnetic resonance imaging (MRI) of the breast has been recently introduced as a potential clinical tool for the detection, diagnosis, staging and management of breast cancer. In this article, we consider the established and evolving roles of MRI with particular reference to screening in high risk women and staging of the primary tumour. Controversies are discussed in the context of the tumour biology and natural history of breast cancer.

METHODS

Articles were identified by searches of PubMed and MEDLINE up to October 2007.

RESULTS

Contrast-enhanced MRI is an effective tool for screening women at high risk of breast cancer. However, randomized trials have yet to demonstrate a reduction in mortality. MRI can also facilitate local staging, in particular, the evaluation of ipsilateral multicentric or multifocal lesions and synchronous contralateral disease which may be 'missed' by conventional imaging. However, efficacy with respect to clinically relevant and patient oriented end-points has yet to be addressed in the context of clinical trials.

CONCLUSIONS

In women at high risk of breast cancer, screening MRI should be used in conjunction with published guidelines. In women with newly diagnosed breast cancer, the utility of MRI is less clearly defined and should be restricted to selected cases within the multidisciplinary setting.