High frame‐rate simultaneous bilateral breast DCE‐MRI

Abstract

A simultaneous bilateral back-projection method for 3D dynamic contrast-enhanced (DCE)-MRI of the breasts was developed and evaluated. Using a double-side band modulation of the RF slab excitation pulse, discontinuous volumes that included both breasts were simultaneously selected. The number of slice phase-encoding steps was undersampled by a factor of 2, and the resulting signal aliasing from one volume to the other was removed using SENSE processing. In-plane encoding was performed with an interleaved radial acquisition reconstructed using dynamic k-space-weighted image contrast (KWIC) temporal filtering. Image resolution was 0.5 ؋ 0.5 ؋ 3.0 mm 3 with an effective temporal resolution of 15 s for both breast volumes. Combined with the 2؋ acceleration from SENSE encoding, this is a 16؋ acceleration factor over a conventional MR bilateral breast scan. An initial evaluation of these methods was performed on a cohort of women who presented with palpable or mammographically visible breast abnormalities. A total of 73 abnormalities were found in 45 of the 54 bilateral examinations that were performed. In 11 of these cases there was a significant finding in the contralateral breast. Dynamic contrast-enhanced (DCE)-MRI of the breast has shown promising results for detecting breast abnormalities (1-4). The architectural features that are visible after enhancement have a high correlation to cancer (5,6), and the enhancement dynamics have also been shown to be highly correlated to benign or malignant lesions (7). Combined interpretations have been shown to improve diagnostic performance compared to that achieved by separate approaches (8 -10). However, even for a unilateral breast study, it is difficult to simultaneously acquire both highspatial-resolution data for architectural analysis and hightemporal-resolution data for contrast kinetic classification because of the different demands involved. The high-resolution images that are necessary to distinguish features for architectural interpretation require a relatively long acquisition time. For example, to image the entire breast, a 3D acquisition of 32 slices with a sampling matrix of 512 ϫ 384 takes ϳ2 min. Acquiring fewer slices or reducing the matrix size will speed acquisition, but at the cost of reduced coverage or spatial resolution. The importance of using a high frame rate for enhancement dynamics analyses was shown by Lucht et al. (11), who observed a significant increase in diagnostic performance when they used 28 points as compared to three time points.As the value of DCE-MRI of the breast becomes appreciated by clinicians and its usage increases, there will be a demand for bilateral acquisitions. However, the problem of imaging at a high frame rate while preserving spatial resolution is compounded in the case of bilateral imaging. In a conventional bilateral examination the acquisitions are interleaved, which doubles the scan repetition time (TR) and reduces the temporal resolution. A coarse representation of the contrast kinetics is the best that can be ac...

Feasibility of high temporal resolution breast DCE‐MRI using compressed sensing theory

“…20 Because of their mutual importance, consistent efforts have been aimed at accomplishing both high temporal and spatial resolution DCE-MRI. [21][22][23][24][25][26][27] A recently developed mathematical theory of signal processing and data acquisition, compressed sensing ͑CS͒ theory, [28][29][30][31] provides a novel way to accomplish this goal. The breakthrough in the CS theory is its ability to allow images to be faithfully recovered from what appear to be highly incomplete data sets, where one of the central tenets of signal processing and data acquisition, the Nyquist sampling theory, has been violated.…”

Independent slab‐phase modulation combined with parallel imaging in bilateral breast MRI

“…In particular, without ISPM the actual physical separation between superimposed slices is a (from medial regions) or 2 a (from lateral regions) but with ISPM the separation is constant (1.5 a ). SENSE reconstruction with a factor of 2 unwraps each pair of two superimposed slices whether ISPM is applied or not [22], but the geometry factors ( g -factors) over the slabs vary due to change of coil sensitivity differences. Changing g -factors by relocating aliasing artifacts is also used in the “controlled aliasing in parallel imaging results in higher acceleration” (CAIPIRINHA) method [23].…”

A comparison of radial keyhole strategies for high spatial and temporal resolution 4D contrast-enhanced MRI in small animal tumor models

“…Numerous methods exist for the implementation of each of the above steps: T1 and M 0 maps can be acquired with several techniques; [3][4][5][6] different mathematical models can be used to analyze the dynamic data; [7][8][9][10][11][12][13][14] and finally, various pulse sequences differing in sampling strategies and acquisition parameters have been developed to sample the signal in k-space. [15][16][17][18] The vast majority of preclinical sampling strategies used for DCE-MRI acquire a limited number of relatively thick slices. Volume averaging and limited coverage make it difficult to characterize the heterogeneity in the tumor microenvironment.…”

“…The work is an extension of previous efforts employing projection imaging with keyhole sampling. 17,[19][20][21] Keyhole sampling, initially defined for rectilinear MRI, 22 refers to a post-acquisition filtering technique in which the center of k-space is updated more frequently than the periphery with the purpose of increasing temporal resolution. Projection imaging, when implemented as a 3D sequence, provides inherently volumetric measurements, has reduced sensitivity to motion and flow artifacts, and allows for shorter echo times as compared to traditional Cartesian methods.…”