Imaging of myocardial infarction for diagnosis and intervention using real-time interactive MRI without ECG-gating or breath-holding

Abstract

Current methods for MRI of infarcted myocardium require ECG-gating and breath-holding during contrast-enhanced segmented k-space inversion-recovery (IR) imaging. However, ECG-gating can be problematic in MRI, and breath-holding can be difficult for some patients. This work demonstrates that infarcted tissue can be visualized without ECG-gating or breath-holding with the use of intermittent inversion pulses during real-time (RT) interactive imaging with steady-state free precession (SSFP). The sequence generates a RT image stream containing a myocardium-nulled image every few frames, which allows nearly simultaneous observation of both infarcted regions and wall motion. First-pass perfusion and wall motion can be simultaneously observed with minor parameter modifications. This method may reduce diagnostic scan time, expand the target population, improve patient comfort, and facilitate targeted, interventional treatment of infarcted myocardium. Supplementary material for this article can be found on the MRM website at http://www.interscience.wiley.com/jpages/0740-3194/suppmat/index.html.

Figures

FIG. 1

Schematic illustration of a pulse sequence for RT-SSFP imaging with intermittent inversion pulses for infarct enhancement. One inversion cycle is shown, starting with an inversion pulse, a myocardium-nulled image, and then several view-shared images during signal recovery. Each slanted line symbolizes a phase-encoding trajectory, plotting ky vs. echo number. The phase-encoding trajectory can be reversed to increase the TI. TD1, TD2, the number of view-shared images, magnetization preparation on/off, and view-sharing on/off can be changed interactively during scanning.

FIG. 2

RT short-axis imaging shortly after systemic 0.2 mM/kg injection of Gd-DTPA in a human with previous MI (consecutive frames). Each view-shared SSFP image was preceded by a 90° nonselective saturation pulse. The image parameters were as follows: TR = 2.84 ms, matrix = 144 × 192, FOV = 300 × 360, 3/4 partial phase k-space acquisition, bandwidth = 1002 Hz/pixel, yielding 2.1 × 1.8 × 6 mm pixels, and 162 ms per view-shared image. An anterior-septal perfusion defect is evidenced in diastolic frames by an arc-shaped hypointense region from 11:00 to 12:00 (arrow), which may be moving out of the imaging slice during systole. The image stream demonstrates simultaneous visualization of first-pass perfusion and wall motion. (Supplementary material for this article can be found on the MRM website at http://www.interscience.wiley.com/jpages/0740-3194/suppmat/index.html.)

FIG. 3

Image stream from RT-IR-SSFP showing DHE in an infarcted pig. Consecutive short-axis images covering two complete inversion cycles 28 min after injection with a TI of 123 ms, and 2.1 × 2.1 × 6 mm pixels. Infarcted myocardial tissue is visible from 9:00 to 12:00 in the myocardium-nulled images (labeled 0 and 812 ms, and displayed more brightly), as well as the four view-shared images. Conventional IR-GRE DHE is displayed for comparison, showing agreement on the region of infarct. RT-IR-SSFP provides additional images for observation of wall motion, and doesn't require ECG-gating or breath-holding.

FIG. 4

Image stream from RT-IR-SSFP showing DHE in a human with previous MI (not the same subject shown in Fig. 2). Consecutive short-axis images covering two complete inversion cycles, 12 min after injection with 2.0 × 1.8 × 6 mm pixels, and 165-ms TI. Infarcted myocardial tissue is visible in the myocardium-nulled images from 8:00 to 2:00, but not as readily in the view-shared images. Conventional IR-GRE DHE image acquired 22 min after injection is displayed for comparison, and shows agreement on the region of infract. RT-IR-SSFP imaging provides additional indications of abnormally low wall thickening and ejection fraction in the same scan.

FIG. 5

RT interactivity facilitates manual optimization of TI (selected, nonconsecutive short-axis frames). Images were acquired from a human (same subject as in Fig. 4) 34 min after Gd-DTPA injection. The TI (displayed on the images) was adjusted in 25-ms increments during RT-IR-SSFP imaging. Four view-shared images (not shown) were acquired between each myocardium-nulled image. Note that a TI of 190 ms suppressed LV blood as well as the normal myocardium, and enhanced visualization of the endocardial border in the infarcted region.

FIG. 6

Nontransmural infarct in a long-axis view: comparison between RT-IR-SSFP without gating or breath-holding and conventional IR-GRE imaging in an infarcted pig, approximately 1 hr after Gd-injection. RT-IR-SSFP imaging (top row, consecutive images) was run with a TI of 150 ms (TD1 = 25 ms) and no view-shared images after each myocardium-nulled image. DHE from the nontransmural infarct (arrow) may be observed simultaneously with wall motion, which appears normal in the infarcted region. The location and size of the infarct compare favorably with conventional IR-GRE (bottom row), which requires ECG-gating and breath-holding.

FIG. 7

Interventional RT imaging example with prototype MR-active catheter (Boston Scientific, Inc.) in an infarcted pig, long-axis view. Images a–c show navigation into the LV cavity using RT-SSFP with view-sharing. Images d–f were acquired using RT-IR-SSFP with TD1 = 50, approximately 40 min after contrast injection. Although the large infarct is visible in all of the images, DHE contrast is best in the myocardium-nulled image (d), especially between the infarct and LV blood. The view-shared images acquired during signal recovery (e–f) show the device position, surrounding anatomy, and wall motion.