Abstract
Objectives
To evaluate the correlation between psoas muscle area (TPA) on CT images and pectoralis muscle area (PMA) on MRI in breast cancer patients.

Methods
This retrospective study was institutional review board approved and women involved gave written informed consent. Twenty six patients with both body CT and breast MRI available were evaluated. Two radiologists calculated TPA on 1.25-mm and 5-mm body CT images. Two radiologists measured PMA on axial T1-weighted images. Statistical analysis included inter- and intra-reader agreement and correlation between TPA on CT and PMA on MRI.

Results
The Pearson r correlation coefficient was 0.70 (95 CI 0.410.81) and the coefficient of determination was 0.49. The inter-reader agreement was k = 0.85 and k = 0.79 for axial 1.25-mm and 5-mm CT images, respectively. The intra-reader agreement of reader 1 was k = 0.98 and k = 0.94 for 1.25-mm and 5-mm CT images, respectively. The intra-reader agreement of reader 2 was k = 0.95 and k = 0.94 for 1.25-mm and 5-mm CT images, respectively. On axial T1-weighted images, the inter-reader agreement for radiologists evaluating the PMA was k = 0.61. Intra-observer agreement of reader 1 and reader 2 for PMA estimation was good (0.62 and 0.64), respectively.

Conclusion
The correlation between TPA on CT images and PMA on MRI was very good. Pectoralis muscle area on breast MRI could be useful to estimate muscle mass in women with breast cancer.