Heart MRI

Tuesday, October 18, 2016

Heart and Great Vessels MRI Scan

MRI of the heart and great vessels are usually done to diagnose and study these common indications:

  • Thoracic aortic aneurysm, dissection and coarctation.
  • Complex congenital abnormalities of the heart and great vessels.
  • Artial or ventriculat septal defect
  • Assesment of ventriculat muscle mass.
  • Vessel patency and thombus
  • Valvular dysfunction

Equipment Needed

  • Body coil volume torso array coil
  • RC bellows
  • ECG leads
  • Ear plugs

Patient Positioning

The patient lies supine on the examination couch with the RC bellows (if required) and ECG gating leads attached. If breath-hold technique is not possible, respiratory gating or triggering is recommended to reduce the respiratory artefacts. The patient is positioned so that the longitudinal alignment light lies in the midline, and the horizontal alignment light passes through the level of the fourth thoracic vertebra, or the nipples. The patient can be placed feet first into the magnet if the ECG trace is unsatisfactory to change the polarity of the patient relative to the main
field of the magnet.

Suggested protocol

A three-plane localizer is optimal as the heart and vascular structures of the chest lie obliquely within the cavity of the chest. The images provided in three orthogonal planes provide a localizer so that oblique views of the heart and great vessels can be prescribed.

Coronal breath-hold fast incoherent (spoiled) GRE/SE T1

Acts as a localizer if three-plane localization is unavailable, or as a diagnostic sequence. Medium slices/gap are prescribed relative to the vertical alignment light, from the posterior chest muscles to the sternum. The area from the top of the sternum to the diaphragm is included in the image.
heart mri
Coronal SE T1 weighted image through the
chest cavity demonstrating slice prescription boundaries and
orientation for axial imaging of the heart.

Axial SE/FSE T1

As for the Coronal T1, except slice thickness/gap is altered to fit the ROI. Prescribe slices from the inferior border of the heart to the superior aspect of the arch of the aorta

Axial T1 weighted FSE image of the
chest using cardiac gating.

Specific Cardiac Views

Long Axis view (two chamber): From the axial T1 projection, using a slice through the left ventricle, align the slice slab parallel to the intraventricular septum and ensure the slab covers the whole of the left ventricle.
heart mri
Axial FSE T1 weighted image showing
slice orientation for the long axis view.

Two chamber long axis view.

Four chamber view: from the long axis view align through the apex of the left ventricle and the mitral valve. Ensure the slice slab covers the whole of the left ventricle. This plane can also be acquired from the short axis view.

Long axis with slice orientation and slice
boundaries for the four chamber view.

Four chamber view.

Short Axis view: from the long axis view align perpendicular to the long axis view imaging plane so that the alignment is parallel to the mitral valve. Ensure the slice slab covers the whole of the left ventricle. The short axis plane can also be prescribed from the coronal localizer. A location can be identified on the coronal localizer, posterior at the aortic root; and another on the coronal by paging the slices anteriorally to the apex of the heart. Once these locations are known, the short axis can be prescribed by explicitly identifying the locations. The scanner will essentially draw an imaginary line between the points and scan perpendicular to that imaginary line. The four chamber view can also be acquired from the short axis view by orientating the slice prescription through the left and right ventricles angled parallel to the diaphragm.

Sagittal/oblique SE T1
As for Axial SE T1, except slices are angled through the ascending and descending aorta and prescribed from one lateral edge of the vessel wall to the other.
This sequence is used to visualize the ascending and descending aorta in one view (candy cane or walking stick view). Select an image from the axial series that demonstrates both portions of the aorta. Check slice position on a more superior slice that demonstrates the arch.

Black blood imaging vs bright blood imaging

SE or FSE images are generally acquired with saturation pulses for the evaluation of black blood. Gradient echo, PC or EPI imaging sequences can be acquired with GMN for the evaluation of bright blood. Other black blood imaging techniques utilize a modified inversion recovery sequence, known as Double IR or Triple IR. Although the various vendors have unique acronyms for these sequences, the premise is the same.
In each case the sequence begins with one 180° RF pulse followed by another 180° RF (double IR). In this case the sequence has essentially been driven to equilibrium. Since flowing blood does not stay within the slice for enough time to experience both 180° RF pulses, flowing blood appears
black. In triple IR sequences, the double IR sequence has an additional 180° pulse at the frequency of fat for spectral presaturation. In this case, the suppression of epicardial fat combined with black flow within the cavity of the heart, allows for better visualization of the myocardium.

Oblique incoherent (spoiled) GRE T1 or coherent GRE T2* multiphase (cine)

Images of the heart, acquired during multiple phases of the cardiac cycle provide cardiac images during the beating of the heart. This technique is known as multiphase imaging. The more slices acquired within each cardiac cycle, the better the temporal resolution (resolution over time). For cardiac imaging temporal resolution, particularly in multiphase imaging, is limited by scan time. For example, if 16 phases of the cardiac cycle are to be acquired during one phase of the cardiac cycle this means that these images are acquired at the same slice location, but at different times
during the cardiac cycle R–R interval. Cardiac cine (like multiphase imaging) is used to assess cardiac function. The most common views for cardiac cine images are the short axis view or the straight axial view of the chest. This view is generally used to evaluate the left ventricle. For other areas of the heart, two chamber or four chamber views may be utilized. Two chambers are best demonstrated on a sagittal/oblique view, four chambers in the coronal/oblique plane. Additional views such as the left ventricular outflow technique may also be useful. Medium slices/gap are prescribed in the plane relevant to the ROI (often axial or oblique). Select the cine functions as appropriate to the system, i.e. number of slices and phases per acquisition

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