Single IR Black Blood
Why go to the trouble of using a double IR method to suppress blood? Couldn't blood be suppressed with a single carefully selected TI value?
|
|
Yes, "black blood" MR images can be produced using a single IR pulse. At 1.5T the T1 value of blood is approximately 1200 msec. Therefore selecting a TInull value of approximately 1200 x (ln 2) = 830 msec would suppress the signal from blood. This was first demonstrated by Mayo et al in 1989.
However, many other tissues, including the myocardium, have T1 values in the same range as blood. Thus using a single IR technique at this TInull will not only suppress the signal from blood, but also the signal of these surrounding tissues. The contrast between blood and the myocardial wall is relatively poor when a single IR technique is used.
Additionally, inflow effects (bringing fully magnetized new blood into the imaging volume) may change the effective T1 of blood within a slice. Hence a single TI value suitable for slowly flowing blood may not effectively suppress the signal from rapidly inflowing blood.
As a result of these limitations and problems, single IR black blood techniques have largely been abandoned in favor of double and triple IR methods.
However, many other tissues, including the myocardium, have T1 values in the same range as blood. Thus using a single IR technique at this TInull will not only suppress the signal from blood, but also the signal of these surrounding tissues. The contrast between blood and the myocardial wall is relatively poor when a single IR technique is used.
Additionally, inflow effects (bringing fully magnetized new blood into the imaging volume) may change the effective T1 of blood within a slice. Hence a single TI value suitable for slowly flowing blood may not effectively suppress the signal from rapidly inflowing blood.
As a result of these limitations and problems, single IR black blood techniques have largely been abandoned in favor of double and triple IR methods.
References
Mayo JR, Culham JAG, MacKay AL, Aikins DG. Blood MR signal suppression by pre-excitation with inverting pulses. Radiology 1989; 173:269-271.
Mayo JR, Culham JAG, MacKay AL, Aikins DG. Blood MR signal suppression by pre-excitation with inverting pulses. Radiology 1989; 173:269-271.