Improved visualization of breast lesions with gadolinium-enhanced magnetization transfer MR imaging

Quantitative Magnetization Transfer Imaging of the Breast at 3.0 T: Reproducibility in Healthy Volunteers

Quantitative magnetization transfer magnetic resonance imaging provides a means for indirectly detecting changes in the macromolecular content of tissue noninvasively. A potential application is the diagnosis and assessment of treatment response in breast cancer; however, before quantitative magnetization transfer imaging can be reliably used in such settings, the technique's reproducibility in healthy breast tissue must be established. Thus, this study aims to establish the reproducibility of the measurement of the macromolecular-to-free water proton pool size ratio (PSR) in healthy fibroglandular (FG) breast tissue. Thirteen women with no history of breast disease were scanned twice within a single scanning session, with repositioning between scans. Eleven women had appreciable FG tissue for test–retest measurements. Mean PSR values for the FG tissue ranged from 9.5% to 16.7%. The absolute value of the difference between 2 mean PSR measurements for each volunteer ranged from 0.1% to 2.1%. The 95% confidence interval for the mean difference was ±0.75%, and the repeatability value was 2.39%. These results indicate that the expected measurement variability would be ±0.75% for a cohort of a similar size and would be ±2.39% for an individual, suggesting that future studies of change in PSR in patients with breast cancer are feasible.

Classification of breast lesions pre-contrast injection using water resonance lineshape analysis

Inhomogeneously broadened, non-Lorentzian water resonances have been observed in small image voxels of breast tissue. The non-Lorentzian components of the water resonance are probably produced by bulk magnetic susceptibility shifts caused by dense, deoxygenated tumor blood vessels (the 'blood oxygenation level-dependent' effect), but can also be produced by other characteristics of local anatomy and physiology, including calcifications and interfaces between different types of tissue. Here, we tested the hypothesis that the detection of non-Lorentzian components of the water resonance with high spectral and spatial resolution (HiSS) MRI allows the classification of breast lesions without the need to inject contrast agent. Eighteen malignant lesions and nine benign lesions were imaged with HiSS MRI at 1.5 T. A new algorithm was developed to detect non-Lorentzian (or off-peak) components of the water resonance. After a Lorentzian fit had been subtracted from the data, the largest peak in the residual spectrum in each voxel was identified as the major off-peak component of the water resonance. The difference in frequency between these off-peak components and the main water peaks, and their amplitudes, were measured in malignant lesions, benign lesions and breast fibroglandular tissue. Off-peak component frequencies were significantly different between malignant and benign lesions (p < 0.001). Receiver operating characteristic (ROC) analysis was used to assess the diagnostic performance of HiSS off-peak component analysis compared with dynamic contrast-enhanced (DCE) MRI parameters. The areas under the ROC curves for the 'DCE rapid uptake fraction', 'DCE washout fraction', 'off-peak component amplitude' and 'off-peak component frequency' were 0.75, 0.83, 0.50 and 0.86, respectively. These results suggest that water resonance lineshape analysis performs well in the classification of breast lesions without contrast injection and could improve the diagnostic accuracy of clinical breast MR examinations. In addition, this approach may provide an alternative to DCE MRI in women who are at risk for adverse reactions to contrast media.

Equivalent cross-relaxation rate imaging in the synthetic copolymer gels and invasive ductal carcinomas of the breast

The values of equivalent cross-relaxation rate (ECR) correlated well with [i] water conditions in various copolymer gels and [ii] nature of malignant cells with regard to nuclear dysplasia and mitotic potential in breast carcinomas. The synthetic copolymer gels composed of any two or three monomers among 2-hydroxyethyl methacrylate (HEMA), glycidyl methacrylate (GMA), N-vinyl-2-pyrrolidinone (N-VP), methyl methacrylate (MMA) and benzyl methacrylate (BMA). The ECR measurement was performed by using an off-resonance saturation pulse under conventional field-echo imaging at frequency within +/- 75 ppm apart from the water resonance frequency. The ECR values were readily to determine and non-time consuming parameter for cross relaxation rate. The ECR values at the frequency offset by 7-ppm (ECR-7) were divided the sample gels two classes, which must correspond to hydrophilic or hydrophobic ones. The sensitivity in the gels was nearly equivalent to the cross-relaxation rate itself. In the breast carcinomas, the ECR-7 correlates with the nature of malignant cells with regard to nuclear dysplasia and mitotic potential. The ECR-7 is better or more accurate than the STR-7 because the SDNRs between carcinoma and glandular tissue increased by approximately 50% on the ECR-7 compared with the STR-7. Thus the ECR values could be a new parameter for malignancy and cell proliferative activity of the breast carcinomas with non-invasive modalities by magnetic resonance imaging.

Saturation transfer ratio imaging in invasive ductal carcinomas of the breast

A prospective study was performed to investigate the correlations between saturation transfer ratio (STR) and histologic parameters of invasive ductal carcinomas in human breast. The histologic parameters investigated were the extent of fibrosis in the intercellular matrix, dysplastic changes of nuclei, and mitotic index. Twenty-seven patients with breast carcinoma were examined using an off-resonance saturation pulse in conjunction with conventional field-echo T(1)-weighted imaging at frequency offsets of 448 Hz and 1200 Hz from water resonance. The values of STR at frequency offset of 1200 Hz (STR(1200)) increased from non-scirrhous carcinoma to scirrhous carcinoma. Although STR(1200) showed correlation with the extent of fibrosis in the intercellular matrix (p<0.01, n = 27), they did not correlate with the dysplastic changes of nuclei or mitotic index. On the other hand, the values of STR at frequency offset of 448 Hz (STR(448)) demonstrated close correlation to dysplastic changes of nuclei and mitotic index (p<0.01, n = 27). STR(1200) correlates with the structural characteristics and STR(448) correlates with the nature of malignant cells with regard to nuclear dysplasia and mitotic potential.

MR state of the art

Magnetic resonance imaging is undergoing continual and progressive evolution. To make a high quality examination, some requirements are mandatory, such as high spatial and contrast resolution to identify lesions and high temporal resolution to characterize them. We review the most important new magnetic resonance technologies, both those which are already available and used in clinical practice and those which are still to be developed. We analyze such technologic and methodolgic features as magnetic field strength, gradients, surface coils, echoplanar imaging, fat suppression techniques and magnetization transfer, contrast agents, automatic injectors, image postprocessing, computer assisted diagnosis, magnetic resonance-guided biopsy and spectroscopy. All these factors are in continuous evolution and new technologies anticipate, in the near future, faster examinations with very high spatial and contrast resolution, with magnetic resonance-guided cytologic and histologic aspiration biopsies, as well as spectroscopic studies of previously identified lesions. To perform a correct, state-of-the-art magnetic resonance examination of the breast, we need high strength gradients with high slew rate and bilateral coils. Finally, we discuss new technologies and methods which will increase the accuracy of magnetic resonance studies of the breast, improving image quality and decreasing execution time. Thus, magnetic resonance spectroscopy, allowing in vivo biochemical tissue analysis, seems to have high potentials; even though they are still difficult to define, the technique is sure to have major diagnostic impact also in monitoring the results to different treatments.

Flip angle dependence of experimentally determined T1sat and apparent magnetization transfer rate constants

The purpose of this work was to develop a method for determining the T1sat and magnetization transfer (MT) rate constants by analyzing the slice-select flip angle dependent MT behavior of normal white and gray matter. The technique uses a high MT power, three-dimensional (3D) gradient-recalled echo (GRE) sequence, with a well chosen MT pulse frequency offset, such that the experimental conditions closely satisfy requisite assumptions for invoking a first order rate process for MT. Integral to this method is that the T1sat and MT ratio values are obtained under explicitly identical MT saturation conditions. The T1sat of white matter was found to be approximately 300 msec, and the MT rate constant was approximately 2.0 sec(-1). The T1sat of gray matter was approximately 500 msec, and the MT rate constant was 1.1 sec(-1). We also found a strong dependence of the MT rate constant on the slice-select flip angle used for the imaging sequence, independent of the MT saturation parameters. Strongly T1-weighted imaging sequences can result in the underestimation of the MT rate constant by 50%. Practical technical suggestions for quantitative MT experiments are put forth.

Power efficient on-resonance saturation pulses for magnetization transfer in magnetic resonance imaging

A family of new on-resonance saturation pulses for magnetization transfer in MRI is proposed. These pulses can be represented as a product of a shaped function and a cosine function. The shaped function can have many different forms, one of which is a Gaussian function. The experimental results on a 1.0 T whole body scanner show that the new on-resonance pulses are more efficient for magnetization transfer than either on-resonance binomial sequence pulses or off-resonance Gaussian pulses at the same power level.