Cardiac (Heart) MRI scan positioning, protocols and planning. Cardiac flow and myocardial T2 mapping

Overview

The video demonstrates a cardiac MRI workflow, from patient preparation and ECG setup through image planning, pre- and post-contrast imaging, aortic flow measurement, and myocardial T2 mapping. It emphasizes accurate localizer images, checking slice positions in multiple views, and using expiration breath-holds for many sequences. Protocols and preferences may vary by institution and scanner.

1. Patient Preparation and Setup

• Complete the MRI safety questionnaire and confirm that the patient is safe to scan.
• Ask the patient to change into a hospital gown with the opening at the front.
• Position the patient head first and supine on the table.
• If needed, shave chest hair before entering the scanner room so ECG electrodes adhere properly.
• Prepare the skin with abrasive gel, then apply MRI-compatible ECG electrodes according to the manufacturer’s instructions.
• Connect the ECG receiver module and check the signal on the scanner display. Reposition the electrodes if the signal is inconsistent or poor.
  • The video illustrates electrode connection on a Siemens scanner.
• Close the gown, place the body coil and spacer cushion over the chest, secure them with a strap, and connect the pressure injector to the IV cannula.
• Give the patient an emergency buzzer and explain how to use it. Provide ear protection, including headphones and earplugs.
• Move the patient into the scanner, center the laser over the mid-chest, and make sure the patient is calm and comfortable.
• In the control room, select or register the patient. Enter accurate height and weight to support specific absorption rate calculations, and register the patient as head first and supine.
• Select the appropriate local protocol in accordance with hospital and radiologist guidelines.

2. Localizers and Cardiac Views

Begin with a three-plane T2 localizer. Good localizers are essential; repeat or re-plan them if the images are inadequate. The video also advises isocentering to the heart to help avoid shimming-related artifacts.

Axial T2 Gradient-Echo Plan

• Plan on the coronal localizer, with the block across the chest.
• Use enough slices to cover the heart from the aortic arch to the apex.
• Check the plan in the other two planes before scanning.

Two-Chamber Localizer

• On the axial image, identify the left ventricular apex and mitral valve angle.
• Align the block through the center of the mitral valve and the left ventricular apex.
• In the sagittal plane, align it parallel to the interventricular septum.
• Acquire as a single slice using an expiration breath-hold.

Short-Axis Localizer

• Plan from the two-chamber view.
• Align the block parallel to the mitral valve plane and perpendicular to the interventricular septum.
• Use the scanner’s perpendicular-planning function if available.
• Acquire with an expiration breath-hold.

Four-Chamber Localizer

• On the two-chamber view, align the block through the mitral valve center and left ventricular apex.
• On the short-axis view, avoid overlapping the aorta; align the block along the right ventricular apex and left anterolateral papillary muscle.
• Acquire with an expiration breath-hold.

3. Cine Imaging

Cine views are generally planned from the localizers and acquired with expiration breath-holds.

• Two-chamber cine: Align through the center of the mitral valve and left ventricular apex. Check the position on the short-axis localizer, bisecting the left ventricle parallel to the interventricular septum.
• Four-chamber cine: If the four-chamber localizer is clear, copy its planning. Check the plan against the two-chamber cine and short-axis localizer.
• Three-chamber cine: On the short-axis localizer, find the slice where the aorta and left ventricle form a “snowman” shape. Plan lengthwise through it, along the centers of the aortic valve and left ventricle. Use perpendicular planning if available.
• Left ventricular outflow tract (LVOT) coronal cine: From the three-chamber cine, align through the centers of the aortic valve and ascending aorta. Use perpendicular planning if available.
• Aortic valve axial cine: Plan from the three-chamber and LVOT coronal cine views, with the block parallel to the aortic annulus. Usually, two or three slices are used for coverage.
• Right ventricular outflow tract (RVOT) cine: The video’s department uses three-point planning:
  1. Place the first point in the right atrium.
  2. Place the second in the middle of the pulmonary trunk.
  3. Place the third at the pulmonary artery bifurcation.

The planner aligns the block along the RVOT, showing the pulmonary valve and pulmonary flow.

4. Optional Morphology Imaging

STIR imaging is described as optional and mainly used to assess myocardial edema, such as in myocarditis.

• Four-chamber STIR: Copy the four-chamber cine planning.
• Two-chamber STIR: Copy the two-chamber cine planning.
• Short-axis STIR: Acquire three individual slices at the apex, mid-ventricular level, and ventricular base. Align perpendicular to the interventricular septum and check the position in the two-chamber view, placing the block perpendicular to the myocardium.
• Perform these scans with expiration breath-holds.

5. Contrast and Post-Contrast Imaging

• Complete the pre-contrast imaging first.
• If contrast is not contraindicated, the video describes administering a double dose of Gadavist using a pressure injector, followed by a normal-saline flush. Immediate post-contrast imaging may help assess blood clots and tumors.
• For post-contrast PSIR imaging, the video’s department prefers free-breathing scans for spatial resolution, though breath-hold scans are also possible. It notes that BSIR sequences use prospective cardiac gating and recommends capturing the cardiac cycle for more accurate gating.
• Plan post-contrast two-, four-, and three-chamber views by copying the corresponding earlier plans.

Short-Axis Cine and TI Scout

Plan short-axis cine slices using the two- and four-chamber cine views:

• Use the two-chamber end-diastolic view, when the heart is at maximal expansion, and align the block parallel to the mitral valve and perpendicular to the myocardium.
• In the four-chamber end-diastolic view, align perpendicular to the interventricular septum.
• Cover the ventricles from the mitral valve to the left ventricular apex.

Acquire with expiration breath-holds, one slice per breath-hold.

Perform a TI scout to identify the myocardial nulling time. The video’s department prefers a short-axis scout, planned from the middle slice of the short-axis cine and acquired during an expiration breath-hold.

Delayed PSIR

• Approximately ten minutes after contrast injection, inspect the TI scout and identify the TI at which the myocardium appears darkest without artifacts. The example shown is 260 ms.
• Enter the selected TI for the two-chamber delayed PSIR scan and copy the earlier two-chamber planning.
• Repeat for the four-chamber delayed scan.
• For delayed short-axis imaging, copy the slice positions and slice numbers from the short-axis cine. Because myocardial nulling time may increase as time passes, the video’s example uses 280 ms for this later scan rather than 260 ms.
• Capture the cardiac cycle for more accurate gating. The video notes that short-axis delayed imaging takes about four to six minutes.
• Normal myocardium appears dark in the delayed PSIR images.

6. Aortic Through-Plane Flow Quantification

The video demonstrates aortic flow as an example of vascular quantitative flow analysis.

Find an Appropriate Velocity

• Use a velocity scout (“VENC scout”) with multiple velocity settings, described as ranging from 50 to 300.
• Plan it perpendicular to the ascending aorta just above the sinotubular junction, using both the three-chamber and LVOT coronal cine views.
• Acquire with an expiration breath-hold.

Select the Flow Velocity

After the scout is complete, review the images. Choose a velocity setting that shows a dark ascending aorta and a bright descending aorta, with no aliasing artifacts.

Acquire Phase-Contrast Flow

Copy the scout planning to the phase-contrast flow sequence. Use the selected velocity setting and acquire with an expiration breath-hold.

7. Myocardial Mapping

The video mentions both T1 and T2 mapping, noting that T1 mapping is performed before and after contrast. It demonstrates T2 mapping.

• Use a three-out-of-five slice-planning technique to place short-axis slices through the mid-myocardium with an appropriate slice gap.
• On the two-chamber end-diastolic view, plan the block parallel to the mitral valve and perpendicular to the myocardium.
• Check the plan in the four-chamber end-diastolic view.
• Initially plan slices with equal gaps to cover the ventricle, then adjust the gap if needed.
• Reduce the slice count to three, which removes the apical and basal slices.
• Check that the coils are on and acquire the mapping scans with expiration breath-holds, one slice per breath-hold.
• Review all images before ending the examination.

Speakers and Sources Featured

• Narrator: An unnamed presenter providing the cardiac MRI workflow and planning instructions.
• Other speakers: None identified in the subtitles.