Feasibility of Quantitative <scp>MRI</scp> Using <scp>3D‐QALAS</scp> for Discriminating Immunohistochemical Status in Invasive Ductal Carcinoma of the Breast

<jats:sec><jats:title>Background</jats:title><jats:p>Two‐dimensional synthetic MRI of the breast has limited spatial coverage. Three‐dimensional (3D) synthetic MRI could provide volumetric quantitative parameters that may reflect the immunohistochemical (IHC) status in invasive ductal carcinoma (IDC) of the breast.</jats:p></jats:sec><jats:sec><jats:title>Purpose</jats:title><jats:p>To evaluate the feasibility of 3D synthetic MRI using an interleaved Look–Locker acquisition sequence with a T2 preparation pulse (QALAS) for discriminating the IHC status, including hormone receptor (HR), human epidermal growth factor receptor 2 (HER 2), and Ki‐67 expression in IDC.</jats:p></jats:sec><jats:sec><jats:title>Study Type</jats:title><jats:p>Prospective observational study.</jats:p></jats:sec><jats:sec><jats:title>Population</jats:title><jats:p>A total of 33 females with IDC of the breast (mean, 52.3 years).</jats:p></jats:sec><jats:sec><jats:title>Field Strength/Sequence</jats:title><jats:p>A 3‐T, 3D‐QALAS gradient‐echo and fat‐suppressed T1‐weighted 3D fast spoiled gradient‐echo sequences.</jats:p></jats:sec><jats:sec><jats:title>Assessment</jats:title><jats:p>Two radiologists semiautomatically delineated 3D regions of interest (ROIs) of the whole tumors on the dynamic MRI that was registered to the synthetic T1‐weighted images acquired from 3D‐QALAS. The mean T1 and T2 were measured for each IDC.</jats:p></jats:sec><jats:sec><jats:title>Statistical Tests</jats:title><jats:p>Intraclass correlation coefficient for assessing interobserver agreement. Mann–Whitney <jats:italic>U</jats:italic> test to determine the relationship between the mean T1 or T2 and the IHC status. Multivariate logistic regression analysis followed by receiver operating characteristics (ROC) analysis for discriminating IHC status. A <jats:italic>P</jats:italic> value <0.05 was considered statistically significant.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>The interobserver agreement was good to excellent. There was a significant difference in the mean T1 between HR‐positive and HR‐negative lesions, while the mean T2 value differed between HR‐positive and HR‐negative lesions, between the triple‐negative and HR‐positive or HER2‐positive lesions, and between the Ki‐67 level > 14% and ≤ 14%. Multivariate analysis showed that the mean T2 was higher in HR‐negative IDC than in HR‐positive IDC. ROC analysis revealed that the mean T2 was predictive for discriminating HR status, triple‐negative status, and Ki‐67 level.</jats:p></jats:sec><jats:sec><jats:title>Data Conclusion</jats:title><jats:p>3D synthetic MRI using QALAS may be useful for discriminating IHC status in IDC of the breast.</jats:p></jats:sec><jats:sec><jats:title>Evidence Level</jats:title><jats:p>1.</jats:p></jats:sec><jats:sec><jats:title>Technical Efficacy</jats:title><jats:p>Stage 2.</jats:p></jats:sec>