Kinetic Analysis of Benign and Malignant Breast Lesions With Ultrafast Dynamic Contrast-Enhanced MRI: Comparison With Standard Kinetic Assessment

Abstract

Objective: The purposes of this study were to evaluate diagnostic parameters measured with ultrafast MRI acquisition and with standard acquisition and to compare diagnostic utility for differentiating benign from malignant lesions.

Materials and methods: Ultrafast acquisition is a high-temporal-resolution (7 seconds) imaging technique for obtaining 3D whole-breast images. The dynamic contrast-enhanced 3-T MRI protocol consists of an unenhanced standard and an ultrafast acquisition that includes eight contrast-enhanced ultrafast images and four standard images. Retrospective assessment was performed for 60 patients with 33 malignant and 29 benign lesions. A computer-aided detection system was used to obtain initial enhancement rate and signal enhancement ratio (SER) by means of identification of a voxel showing the highest signal intensity in the first phase of standard imaging. From the same voxel, the enhancement rate at each time point of the ultrafast acquisition and the AUC of the kinetic curve from zero to each time point of ultrafast imaging were obtained.

Results: There was a statistically significant difference between benign and malignant lesions in enhancement rate and kinetic AUC for ultrafast imaging and also in initial enhancement rate and SER for standard imaging. ROC analysis showed no significant differences between enhancement rate in ultrafast imaging and SER or initial enhancement rate in standard imaging.

Conclusion: Ultrafast imaging is useful for discriminating benign from malignant lesions. The differential utility of ultrafast imaging is comparable to that of standard kinetic assessment in a shorter study time.

Keywords: MRI; breast; cancer; kinetics; ultrafast.

Figures

Fig. 1—

Diagram shows protocols for ultrafast and standard MRI. Ultrafast temporal resolution is 7 seconds; standard, 65 seconds.

Fig. 2—

69-year-old woman with grade 3 invasive ductal carcinoma of left breast. A, Color-coded map of standard MR image shows cursor points at voxel with highest signal intensity in lesion. B, Graph shows kinetic curve corresponding to A. C, MR image obtained with ultrafast technique shows location of cursor in A. In this patient, contrast enhancement in aorta is visible at first time point (C1) on ultrafast image. D, Graph shows kinetic curve corresponding to C.

Fig. 3—

Graph shows kinetic AUC of time point x to time point x + 1 as trapezoid (gray), which represents AUC of time points 3 and 4. Kinetic AUC for multiple time points can be obtained by addition of each trapezoid from neighboring time points. Dashed line represents y = 0.

Fig. 4—

47-year-old woman with metastatic carcinoma of left breast. Series of images from ultrafast acquisition (time points 1–8) and image of same slice on standard (Regular) image (first time point). Image obtained at first time point of ultrafast acquisition (C1) shows R0I (circle) on aorta shows more than two times signal intensity of same area on unenhanced image. Therefore, this image becomes C1. On C2 image, malignant tumor (metaplastic carcinoma) becomes visible (thick arrow), as do internal mammary arteries (thin arrows). C3 image shows background parenchymal enhancement (arrows) gradually emerging. Standard image shows degree of background parenchymal enhancement (thin arrows) becoming approximately same as signal intensity of tumor (thick arrow).

Fig. 5—

Graph shows ROC curves of enhancement rate at second time point of ultrafast acquisition (C2) and signal enhancement ratio (SER) and initial enhancement rate (IER) of standard image.