Table 1 Factors that impact the use of ASL in heart and in the brain, for measuring myocardial blood flow (MBF) and cerebral blood flow (CBF), respectively

Tissue Blood Flow

0.5 – 1.5 mL/g/min (rest)

3.0 – 5.0 mL/g/min (stress)

0.35 – 0.55 mL/g/min [100]

Water Kinetics

Instantaneous exchange

Decreased water exchange due to blood brain barrier (BBB)

Blood pathway

Many directions; Blood passes through left atrium, left ventricle, aortic root, coronary arteries and then myocardium.

Unidirectional; Internal carotids and vertebral arteries deliver blood to the Circle of Willis, then to branch vessels, then to the brain. Blood flowing primarily inferior to superior.

Motion

Significant cardiac motion; Quiescent periods are:

End systole: ~80 ms long

Mid diastole: 0-150 ms long depending on heart rate.

Respiratory motion must be handled either by limiting the acquisition time to a breath-hold or by correcting for motion

Insignificant motion compared to the spatial resolution typically used (~2 mm).

Intrinsic SNR efficiency

1/3 of Brain (normal weight subjects); due to larger distance from receiver coil elements and larger noise volume

Imaging Concerns

Imaging must be performed during quiescent cardiac phases.

Labeling Concerns

Direction of Flow

Pulsatile Flow

Cardiac Motion

Maximum efficiency (pseudo-continuous labeling recommended [26])

Optimal Readouts

For maximum myocardial signal:

Snapshot balanced SSFP

Single-shot EPI

For maximum gray/white matter signal:

Single-shot Spiral

Single-shot EPI