Characterizing Stiffness of Human Prostates Using Acoustic Radiation Force

Acoustic Radiation Force Impulse (ARFI) imaging has been previously reported to portray normal anatomic structures and pathologies in er vivo human prostates with good contrast and resolution These findings were based on comparison with histological slides and McNeal s zonal anatomy In ARFI images the central zone (CZ) appears darker (smaller displacement) than other anatomic zones and prostate cancer (PCa) is darker than normal tissue in the peripheral zone (PZ) Since displacement amplitudes in ARFI images are determined by both the underlying tissue stiffness and the amplitude of acoustic rail anon force that vanes with acoustic attenuation one question that arises is how the relative displacements in prostate ARFI images are related to the underlying prostatic tissue stiffness In linear isotropic elastic materials and in tissues that are relatively uniform in acoustic attenuation (e g liver) relative displicement in ARFI images has been shown to be correlated with underlying tissue stiffness However the prostate is known to be heterogeneous Variations in acoustic attenuation of prostatic structures could confound the interpretation of ARFI images due to the associated variations in the applied acoustic radiation force Therefore in this study co registered three dimensional (3D) ARFI datasets and quantitative shear wave elasticity imaging (SWEI) datasets were acquired in freshly excised human prostates to investigate the relationship between displacement amplitudes in ARFI prostate images and the m itched reconstructed shear moduli The lateral time to peak (LTTP) algorithm was applied to the SWEI data to compute the shear wave speed and reconstruct the shear moduli Five types of prostatic tissue (PZ CZ transition zone (TZ) and benign prostatic hyperplasia (BPH) PCa and atrophy) were identified whose shear moduli were quantified to be 4 1 +/- 0 8 kPa, 9 9 +/- 0 9 kPa, 4 8 +/- 0 6 kPa, 10 0 +/- 1 0 kPa and 8 0 kPa respectively Linear regression was per formed to compare ARFI displacement amplitudes and the Inverse of the corresponding reconstructed shear moduli at multiple depths The results indicate an inverse relation between ARFI displacement amplitude and reconstructed shear modulus at all depths These findings support the conclusion that ARFI prostate Images portray underlying tissue stiffness variations