Application of an exogenous hyperoxic contrast agent in MR mammography: initial results

Prognostic Significance of Transverse Relaxation Rate (R2*) in Blood Oxygenation Level-Dependent Magnetic Resonance Imaging in Patients with Invasive Breast Cancer

Objective

To examine the relationship between magnetic resonance transverse relaxation rate (R2*) and prognostic factors.

Materials and Methods

A total of 159 women with invasive ductal carcinomas (IDCs) underwent breast magnetic resonance imaging (MRI) including blood oxygenation level-dependent (BOLD) sequence at 3 T. The distribution of the measured R2* values were analyzed, and the correlation between R2* and various prognostic factors (age, tumor size, histologic grade, lymphovascular invasion, and axillary lymph node status, as well as expression of estrogen receptor, progesterone receptor, human epidermal growth factor receptor 2, p53, and Ki-67) were retrospectively assessed using patient medical records.

Results

The baseline R2* values of the IDCs were very heterogeneous with wide range among the patients. The mean R2* value was (32.8 ± 14.0) Hz with a median of 29.3 Hz (range 13.5–109.4 Hz). In multivariate analysis, older age was associated with decreased R2* value (P = 0.011) and IDCs with p53-overexpression showed higher R2* values than those without p53-overexpression group (P = 0.031). Other prognostic factors were not significantly correlated with R2* value.

Conclusion

In this study, R2* values were significantly correlated with age and expression of p53. Further studies are necessary to determine the prognostic value of BOLD-MRI.

Near infrared transillumination imaging of breast cancer with vasoactive inhalation contrast

Inhalation of vasoactive gases such as carbon dioxide and oxygen can provide strong changes in tissue hemodynamics. In this report, we present a preliminary clinical study aimed at assessing the feasibility of inhalation-based contrast with near infrared continuous wave transillumination for breast imaging. We describe a method for fitting the transient absorbance that provides the wavelength dependence of the optical pathlength as parametrized by tissue oxygenation and scatter power as well as the differential changes in oxy- and deoxy-hemoglobin. We also present a principal component analysis data reduction technique to assess the dynamic response from the tissue that uses coercion to provide single temporal eigenvalues associated with both oxy- and deoxy-hemoglobin changes.

Intrinsic susceptibility MR imaging of chemically induced rat mammary tumors: relationship to histologic assessment of hypoxia and fibrosis

PURPOSE

To investigate relationships between magnetic resonance (MR) imaging measurements of R2* and carbogen-induced DeltaR2* in vivo with subsequent histologic assessment of grade, hypoxia, fibrosis, and necrosis in a chemically induced rat mammary tumor model.

MATERIALS AND METHODS

All experiments were performed in accordance with the local ethics review panel, the UK Home Office Animals Scientific Procedures Act of 1986, and the UK Co-ordinating Committee on Cancer Research guidelines. Of 30 rats injected with N-methyl-N-nitrosourea, 17 developed mammary tumors. Prior to MR imaging, rats were administered pimonidazole. Tumor R2* was then quantified while the host first breathed air and then carbogen (95% O(2), 5% CO(2); n = 16). Tumor sections were subsequently stained for pimonidazole, sirius red, cytokeratin 14, and hematoxylin-eosin for quantitative assessment of hypoxia, fibrosis, malignancy, and necrosis, respectively, and graded according to the Scarff-Bloom-Richardson scale. Linear regression analysis was used to identify any correlates of the MR imaging data with histologic data.

RESULTS

Tumors exhibited wide heterogeneity in the magnitude of carbogen-induced reduction in R2*, an emerging imaging biomarker of fractional blood volume. Significant correlations were found between pimonidazole adduct formation and both baseline tumor R2* (r = -0.54, P = .03) and carbogen-induced DeltaR2* (r = 0.56, P = .02), demonstrating that tumors with a larger fractional blood volume were less hypoxic. There was also a significant correlation between pimonidazole and sirius red staining (r = 0.76, P < .01), indicating that more fibrotic tumors were also more hypoxic. There were no correlations of R2* with grade.

CONCLUSION

In this model of breast cancer, baseline tumor R2* and carbogen-induced DeltaR2* are predictive imaging biomarkers for hypoxia and primarily determined by blood volume.