Basics of Cardiac MRI

Uses:      Congenital Heart Disease, masses, pericardium, Right  ventricular dysplasia, Hibernating myocardium (presently).MR gives more  temporal  and  contrast resolution  vs CT giving more spatial resolution Myocardial perfusion and Ventricular as well as valvular functions are very accurate on MR, but presently clinical science  uses Echo and SPECT studies for them.

Imaging Planes:     Main planes are oblique  to one another , and as they are at arbitrary angles  to the scanner , referred to as ” Double Obliques”

3 Most important  (a) short axis -take 4 chamber  gradient echo axial -----plan perpendicular to ventricular septum----- gives short axis

(b)Horizontal  long Axis   (Long axis- from center of mitral valve to  LV apex) (4 chamber view)

(c) Vertical Long Axis (2 chamber view)

Others include  LV Out flow tract view(Ascending aorta best ) and 3 chamber view (aortic and mitral valves adjacent to each other )

ECG Gating  acquisition is usually the norm (firing usually in  Trigger window of diastolic  phase =typically 10 to 15% R -R interval)(Acquisition window  is  85 to 90 % of R R interval) . Problems with this gating include poor or inaccurate R  wave  and arrhythmias (handled  by medication or very fast sequences )

 Sequences can be summed up depending on main uses

Cardiac  Function: Cine Gradient echo sequences (Bright Blood ) include True FISP(Siemens),FIESTA(GE), and b-FFE(Philips)

Morphology  Function: Half Fourier  single shot fast spin echo sequences(Black blood)  used  include HASTE(Siemens) and SS-FSE( GE and Philips)

Perfusion Function: Magnetization-prepared gradient echo sequences are used to assess myocardial perfusion     .Turbo  FLASH (siemens),Fast SPGR (GE) , and TFE(Philips)

Viability/ infarction: Contrast enhanced  Inversion recovery gradient echo   sequence is used with inversion  time set to  null  viable  myocardium .

Angiography: not popular and uses 2D or 3D Gradient echo sequences

Black Blood  !

Protons must experience the 90° excitation pulse and the 180° refocusing pulse to generate a spin echo. If protons in flowing blood are not present in the slice long enough to experience both pulses, no spin echo is generated

What should I Use?

Fastest- half fourier  Single shot fast Spin Echo (SSFSE) with double inversion recovery time – done in 1 heart beat

Breath hold  SSFSE with inversion recovery time   - done as 1 slice per breath   to give better resolution

Multislice  FSE with free breathing