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
Basics of Cardiac MRI Reviewed by Sumer Sethi on Friday, December 09, 2011 Rating: