Correcting time-intensity curves in dynamic contrast-enhanced breast MRI for inhomogeneous excitation fields at 7T.

PURPOSE: Inhomogeneous excitation at ultrahigh field strengths (7T and above) compromises the reliability of quantified dynamic contrast-enhanced breast MRI. This can hamper the introduction of ultrahigh field MRI into the clinic. Compensation for this non-uniformity effect can consist of both hardware improvements and post-acquisition corrections. This paper investigated the correctable radiofrequency transmit ( B1+ ) range post-acquisition in both simulations and patient data for 7T MRI. METHODS: Simulations were conducted to determine the minimum B1+ level at which corrections were still beneficial because of noise amplification. Two correction strategies leading to differences in noise amplification were tested. The effect of the corrections on a 7T patient data set (N = 38) with a wide range of B1+ levels was investigated in terms of time-intensity curve types as well as washin, washout and peak enhancement values. RESULTS: In simulations assuming a common amount of T1 saturation, the lowest B1+ level at which the SNR of the corrected images was at least that of the original precontrast image was 43% of the nominal angle. After correction, time-intensity curve types changed in 24% of included patients, and the distribution of curve types corresponded better to the distribution found in literature. Additionally, the overlap between the distributions of washin, washout, and peak enhancement values for grade 1 and grade 2 tumors was slightly reduced. CONCLUSION: Although the correctable range varies with the amount of T1 saturation, post-acquisition correction for inhomogeneous excitation was feasible down to B1+ levels of 43% of the nominal angle in vivo.

Monitoring tumor response to neoadjuvant chemotherapy using MRI and 18F-FDG PET/CT in breast cancer subtypes.

PURPOSE: To explore guidelines on the use of MRI and PET/CT monitoring primary tumor response to neoadjuvant chemotherapy (NAC), taking breast cancer subtype into account. MATERIALS AND METHODS: In this prospective cohort study, 188 women were included with stages II and III breast cancer. MRI and 18F-FDG-PET/CT were acquired before and during NAC. Baseline pathology was assessed from tumor biopsy. Tumors were stratified into HER2-positive, ER-positive/HER2-negative (ER-positive), and ER-negative/PR-negative/HER2-negative (triple-negative) subtypes, and treated according to subtype. Primary endpoint was pathological complete response (pCRmic) defined as no or only small numbers of scattered invasive tumor cells. We evaluated imaging scenarios using MRI only, PET/CT only, and combinations. RESULTS: pCRmic was found in 35/46 (76.1%) of HER2-positive, 11/87 (12.6%) of ER-positive, and 31/55 (56.4%) of triple-negative tumors. For HER2-positive tumors, MRI yielded the strongest predictor (AUC: 0.735; sensitivity 36.2%), outperforming PET/CT (AUC: 0.543; p = 0.04), and with comparable results to combined imaging (AUC: 0.708; p = 0.213). In ER-positive tumors, the combination of MRI and PET/CT was slightly superior (AUC: 0.818; sensitivity 55.8%) over MRI alone (AUC: 0.742; p = 0.117) and PET/CT alone (AUC: 0.791). However, even though relatively large numbers of ER-positive tumor patients were included, no significant differences were yet found. For triple-negative tumors, MRI (AUC: 0.855; sensitivity 45.4%), PET/CT (AUC: 0.844; p = 0.220) and combined imaging (AUC: 0.868; p = 0.213) yielded comparable results. CONCLUSIONS: For HER2-positive tumors, MRI shows significant advantage over PET/CT. For triple-negative tumors, comparable results were seen for MRI, PET/CT and combined imaging. For ER-positive tumors, combining MRI with PET/CT may result in optimal response monitoring, although not yet significantly.

Fat suppression techniques for obtaining high resolution dynamic contrast enhanced bilateral breast MR images at 7T.

OBJECTIVES: To compare water selective excitation (WSE) and Dixon fat suppression in the context of high-resolution dynamic contrast enhanced MRI of the breast at 7T. METHODS: Ten healthy volunteers and one patient with a malignant breast lesion were scanned at 7T. The MRI protocol contained 3D T1-weighted gradient echo images obtained with both WSE fat suppression, multi echo Dixon fat suppression, and without fat suppression. Images were acquired at a (0.8mm)(3) or (0.7mm)(3) isotropic resolution with equal field of view and optimized such to obtain a maximal SNR. Image quality was scored qualitatively on overall image quality, sharpness of anatomical details, presence of artifacts, inhomogeneous fat suppression and the presence of water-fat shift. A quantitative scoring was obtained from the signal to noise ratio and contrast to noise ratio. RESULTS: WSE scored significantly better in terms of overall image quality and the absence of artifacts. No significant difference in contrast to noise ratio was found between the two fat suppression methods. CONCLUSION: When maximizing temporal and spatial resolution of high resolution DCE MRI of the breast, water selective excitation provides better image quality than multi echo Dixon at 7T.

Multiparametric MRI With Dynamic Contrast Enhancement, Diffusion-Weighted Imaging, and 31-Phosphorus Spectroscopy at 7 T for Characterization of Breast Cancer.

OBJECTIVES: To describe and to correlate tumor characteristics on multiparametric 7 tesla (T) breast magnetic resonance imaging (MRI) with prognostic characteristics from postoperative histopathology in patients with breast cancer. MATERIALS AND METHODS: Institutional review board approval and written informed consent of 15 women (46-70 years) with 17 malignant lesions were obtained. In this prospective study (March 2013 to March 2014), women were preoperatively scanned using dynamic contrast-enhanced MRI, diffusion-weighted imaging, and 31-phosphorus spectroscopy (¹³P-MRS). The value of the protocol was assessed to quantify tumor differentiation and proliferation. Dynamic contrast-enhanced MRI was assessed according to the American College of Radiology Breast Imaging Reporting and Data System-MRI lexicon. Apparent diffusion coefficients (ADCs) were calculated from diffusion-weighted imaging. On ¹³P-MRS, at the location of the tumor, the amount of phosphorus components was obtained in a localized spectrum. In this spectrum, the height of phosphodiester (PDE) and phosphomonoester (PME) peaks was assessed to serve as a measure for metabolic activity, stratifying tumors into a PDE > PME, PDE = PME, or PDE < PME group. Tumor grade and mitotic count from resection specimen were compared with the MRI characteristics using explorative analyses. RESULTS: On dynamic contrast-enhanced MRI, the mean tumor size was 24 mm (range, 6-55 mm). An inverse trend was seen between ADC and tumor grade (P = 0.083), with mean ADC of 867 × 10⁻6 mm²/s for grade 1 (N = 4), 751 × 10⁻6 mm²/s for grade 2 (N = 6), and 659 × 10⁻6 mm²/s for grade 3 (N = 2) tumors. Between P-MR spectra and mitotic count, a relative increase of PME over PDE showed significant association with increasing mitotic counts (P = 0.02); a mean mitotic count of 6 was found in the PDE greater than PME group (N = 7), 8 in the PDE = PME group (N = 1), and 17 in the PDE < PME group (N = 3). CONCLUSIONS: Multiparametric 7 T breast MRI is feasible in clinical setting and shows association between ADC and tumor grade, and between ¹³P-MRS and mitotic count.

Association between rim enhancement of breast cancer on dynamic contrast-enhanced MRI and patient outcome: impact of subtype.

The heterogeneous nature of breast cancer is represented by three breast cancer subtypes associated with different patient outcome. However, within subtypes, variations still exist. Additional stratification is necessary for more individualized therapy. Functional tumor characteristics on dynamic contrast-enhanced (DCE)-MRI may play a role. Rim enhancement of breast cancers has been associated with unfavorable pathology characteristics in the context of outcome. However, existence of a direct link is unknown. The purpose was to retrospectively determine the association between rim enhancement on DCE-MRI and long-term patient outcome, and whether it has complementary value to subtype. Preoperative DCE-MRI was performed in 556 consecutive female patients who were eligible for breast-conserving therapy. Presence of rim enhancement was assessed. Tumor characteristics were derived from resection specimens. Patients were stratified according to subtype. Association was assessed between rim enhancement and patient, pathology and treatment characteristics, recurrence-free interval and invasive disease-free survival. Median follow-up was 84 months. Patients were stratified into ER-positive/HER2-negative (N = 416), HER2-positive (N = 75), or triple-negative (N = 65) subtypes. Rim enhancement was seen in 29.0% (N = 161/556) of tumors and was associated with higher histologic grade, negative ER-status, and triple-negative subtype. Only within triple-negative tumors, an association was seen with outcome. Recurrence was lower in non-rim-enhancing tumors (N = 1/36; 2.8%) compared to rim-enhancing tumors (N = 9/28; 32.1%) (p = 0.001). Survival was higher in non-rim-enhancing tumors (N = 34/36; 94.4%) compared to rim-enhancing tumors (N = 18/28; 64.3%) (p = 0.001). Rim enhancement on DCE-MRI is associated with long-term outcome of patients with triple-negative breast cancer and may potentially serve as a prognostic biomarker in these patients.

Agreement on indication for systemic therapy between biopsied tissue and surgical excision specimens in breast cancer patients.

PURPOSE: In breast cancer therapy, the indication for systemic therapy is typically based on prognostic markers from the surgical excision specimen. If such is unavailable, for instance prior to tumor ablation therapy, the indication for adjuvant systemic therapy may be assessed from pretreatment biopsies. The effect of differences in tumor characteristics between biopsy and excision specimen on agreement in indication for systemic therapy is, however, largely unknown. The aim of this study is to determine the agreement in eligibility for systemic therapy between preoperative and postoperative assessment. Secondly, to identify which patient-, tumor- or lymph node characteristics may influence this agreement. MATERIALS AND METHODS: In this retrospective study, 300 consecutive female patients with primary invasive breast carcinoma on biopsy were included. Indication for systemic therapy was determined separately from biopsied tissue and from excision specimens using national guidelines based on adjuvant! online. Agreement was assessed, and patient-, tumor- and lymph node characteristics affecting agreement analyzed. RESULTS: Agreement in tumor characteristics between biopsy and excision specimen varied from high (ER-status: 99%), to lower (tumor grade: 62%, tumor size: 59%, and lymph node status: 67%). Without preoperative sentinel node biopsy (SNB), agreement on systemic therapy exists in 77% of patients (kappa = 0,547). Positive pretreatment indication for systemic therapy was highly indicative of the postoperative indication (PPV = 94%). Negative indication was, however, only indicative in 67% of patients. Conversely, with preoperative SNB, agreement on negative indication was raised to 89%. Agreement was especially high for ER-negative status, tumor grade 3, tumor size >2 cm, lymph node positivity at biopsy and a negative preoperative SNB. CONCLUSIONS: A positive indication for systemic therapy from biopsy is highly indicative for a positive indication from the excision specimen. When the indication is negative, additional stratification using preoperative SNB raises the agreement. Still, discordance occurs in 1 out of 10 patients.