Correlation between SWEI and ARFI image findings in ex vivo human prostates

Acoustic Radiation Force Impulse (ARFI) imaging has previously been used to visualize normal anatomic structures and pathologies in both ex vivo and in vivo human prostates. Based on the relative displacement amplitudes in ARFI images and comparison with histological slides and McNeal's zonal anatomy, it seems that the central zone (CZ) is stiffer than other anatomic zones, and prostate cancer (PCa) is stiffer than normal tissue in the peripheral zone and benign prostatic hyperplasia (BPH). Since displacement amplitudes in ARFI images are determined by both the underlying tissue stiffness and the amplitude of acoustic radiation force, one question that arises is: how are the relative displacements in ARFI images related to the underlying tissue stiffness? In this study, co-registered three-dimensional (3D) ARFI datasets and shear wave elasticity imaging (SWEI) datasets were acquired to investigate the relationship between displacement amplitudes in ARFI images and the underlying tissue stiffness. Six freshly excised human prostates were collected and imaged. The lateral time-to-peak (TTP) algorithm was used to reconstruct the tissue stiffness. Linear regression was performed between ARFI displacement amplitudes and the inverse of the corresponding reconstructed shear moduli. Five types of prostatic tissues were identified in ARFI images, and their stiffnesses were quantified.