In vivo 1H MRS in the assessment of the therapeutic response of breast cancer patients

Abstract

MRI and in vivo MRS have rapidly evolved as sensitive tools for diagnosis and therapeutic monitoring in cancer research. In vivo MRS provides information on tumor metabolism, which is clinically valuable in the diagnosis and assessment of tumor response to therapy for the management of women with breast diseases. Several centers complement breast MRI studies with (1)H MRS to improve the specificity of diagnosis. Malignant breast tissues show elevated water-to-fat ratio and choline-containing compounds (total choline, tCho), and any effect of therapy on tissue viability or metabolism will be manifested as changes in these levels. Sequential (1)H MRS studies have shown significantly reduced tCho levels during the course of therapy in patients who were responders. However, there are challenges in using in vivo MRS because of the relatively low sensitivity in detecting the tCho resonance with decreased lesion size or significant reduction in the tumor volume during therapy. MRS is also technically challenging because of the low signal-to-noise ratio and heterogeneous distribution of fat and glandular tissues in the breast. MRS is best utilized for the diagnosis of focal masses, most commonly seen in patients with ductal-type neoplasms; however, it has limitations in detecting nonfocal masses, such as the linear pattern of tumors seen in invasive lobular carcinoma. Further work is required to assess the clinical utility of quantitative MRS, with the goal of automation, which will reduce the subjectivity currently inherent in both qualitative and semi-quantitative MRS.

Figure 1

(A) MRI showing the voxel position from which the single-voxel (SV) ¹H MR in vivo spectrum (B) was obtained from the normal breast tissue of a volunteer [without water and fat (lipid) suppression].

Figure 2

(A) MRI of a patient with locally advanced breast cancer showing the voxel position from which the single-voxel (SV) ¹H MR in vivo spectrum was obtained without water and fat (lipid) suppression (B) and with the suppression of water + fat (lipid) resonances (C).

Figure 3

Graph showing an individual patient’s pre- and post-therapy water-to-fat (W–F) ratios. [Reprinted with permission of Wiley-Liss, Inc., a subsidiary of John Wiley & Sons, Inc., from ref. (34).]

Figure 4

(A) Pre-therapy T₂-weighted sagittal fat-suppressed image of a patient with locally advanced breast cancer who was a responder with the MRSI grid. (B) Spectrum obtained from a voxel highlighted in (A) showing the total choline (tCho) signal. (C) Post-therapy MRI of the same patient after the third cycle of neoadjuvant chemotherapy (NACT). (D) Spectrum obtained from a voxel highlighted in (C) that showed no tCho. [Reproduced with permission from John Wiley & Sons from ref. (42).]

Figure 5

(A) Pre-therapy T₂-weighted sagittal fat-suppressed image of a patient with locally advanced breast cancer who was a nonresponder with the MRSI grid. (B) Spectrum obtained from a voxel highlighted in (A) showing the total choline (tCho) signal. (C) Post-therapy T₂-weighted sagittal fat-suppressed image of the same patient after the third cycle of neoadjuvant chemotherapy (NACT). (D) Spectrum obtained from a voxel highlighted in (C) showing the tCho signal. [Reproduced with permission from John Wiley & Sons from ref. (42).]

Figure 6

(A) Pre-therapy T₂-weighted sagittal fat-suppressed image of a patient with locally advanced breast cancer who was a responder, showing the voxel from which the single-voxel (SV) ¹H MR spectrum (B) was obtained. (C) Post-therapy T₂-weighted sagittal fat-suppressed image of the same patient, showing the voxel from which the ¹H MR spectrum (D) was obtained with reduced total choline (tCho) concentration.