Tissue pulsatility imaging: Ultrasonic measurement of strain due to perfusion

Over each cardiac cycle perfused tissues expand and relax by a fraction of a percent as blood rapidly accumulates in the arterial vasculature during systole and then slowly drains through the venous vasculature during diastole. Tissue pulsatility imaging (TPI) is a variation on ultrasonic tissue strain imaging that estimates tissue perfusion from this natural, cyclic tissue expansion and relaxation. TPI is derived in principle from plethysmography, a century‐old technology for measuring gross tissue volume change from a whole limb or other isolatable body part. With TPI, the plethysmographic signal is measured from hundreds or thousands of sample volumes within an ultrasound image plane to characterize the local perfusion throughout a body part. TPI measures tissue strain over the cardiac cycle and parametrizes the signal in terms of its amplitude and shape. The amplitude of the strain waveform is correlated with perfusion, and the shape of the waveform is correlated with vascular resistance. Results will be presented from the leg showing the change in the TPI signals as the muscles recover from exercise, from breast tumors, and from the brain as blood flow changes in response to visual stimulation. [Work supported in part by NIH 1‐R01EB002198‐01 and NIH N01‐CO‐07118.]