Prostate Cancer Detection Using 3-D Shear Wave Elasticity Imaging

Abstract

Transrectal ultrasound (TRUS) B-mode imaging provides insufficient sensitivity and specificity for prostate cancer (PCa) targeting when used for biopsy guidance. Shear wave elasticity imaging (SWEI) is an elasticity imaging technique that has been commercially implemented and is sensitive and specific for PCa. We have developed a SWEI system capable of 3-D data acquisition using a dense acoustic radiation force (ARF) push approach that leads to enhanced shear wave signal-to-noise ratio compared with that of the commercially available SWEI systems and facilitates screening of the entire gland before biopsy. Additionally, we imaged and assessed 36 patients undergoing radical prostatectomy using 3-D SWEI and determined a shear wave speed threshold separating PCa from healthy prostate tissue with sensitivities and specificities akin to those for multiparametric magnetic resonance imaging fusion biopsy. The approach measured the mean shear wave speed in each prostate region to be 4.8 m/s (Young's modulus E = 69.1 kPa) in the peripheral zone, 5.3 m/s (E = 84.3 kPa) in the central gland and 6.0 m/s (E = 108.0 kPa) for PCa with statistically significant (p < 0.0001) differences among all regions. Three-dimensional SWEI receiver operating characteristic analyses identified a threshold of 5.6 m/s (E = 94.1 kPa) to separate PCa from healthy tissue with a sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and area under the curve (AUC) of 81%, 82%, 69%, 89% and 0.84, respectively. Additionally, a shear wave speed ratio was assessed to normalize for tissue compression and patient variability, which yielded a threshold of 1.11 to separate PCa from healthy prostate tissue and was accompanied by a substantial increase in specificity, PPV and AUC, where the sensitivity, specificity, PPV, NPV and AUC were 75%, 90%, 79%, 88% and 0.90, respectively. This work illustrates the feasibility of using 3-D SWEI data to detect and localize PCa and demonstrates the benefits of normalizing for applied compression during data acquisition for use in biopsy targeting studies.

Keywords: Acoustic radiation force impulse imaging; Elasticity imaging; Prostate cancer; Shear wave elasticity imaging.

Figure 1:

The axial histology slide corresponding to the center of a Gleason grade group 3 (Gleason 4+3=7) PCa foci, with the prostate capsule (black), Gleason pattern 4 PCa (purple), and Gleason pattern 3 PCa (green) also indicated. B. TRUS in vivo axial B-mode image from the matched region in the prostate which was used to identify and segment the prostate capsule (green). C. Matched in vivo ARFI axial image which was used to identify and segment the CG (black). D. Matched in vivo SWEI axial image indicating both the capsule and CG segmentations along with the PCa segmentation (purple). E. in vivo SWEI coronal image corresponding to a plane bisecting the PCa along the dashed black line in D with the capsule (green), CG (black) and PCa (purple) also included. F. 3D visualization of the segmented prostate capsule (green) and PCa (purple, arrow). In subplots C-E, voxels which did not meet the data quality requirements were excluded (blue). PCa = prostate cancer; TRUS = transrectal ultrasound; ARFI = acoustic radiation force impulse; CG = central gland; SWEI = shear wave elasticity imaging;

Figure 2:

Boxplots representing the mean SWS values in each prostate versus the prostate region (PZ – peripheral zone; CG – central gland; PCa – segmented prostate cancer). Each column contains data from 36 patients. Statistically significant differences (p<0.0001) are indicated by asterisks (*). SWS = shear wave speed.

Figure 3:

Boxplots representing the mean SWS values in each PCa foci grouped by Gleason grade group (GG). The number of cancerous regions is indicated for each grade group. No statistically different (p<0.05) relationships were identified between grade groups. SWS = shear wave speed.

Figure 4:

Boxplots representing the ratio of the regional mean SWS to the entire prostate mean SWS versus the prostate region (PZ – peripheral zone; CG – central gland; PCa – segmented prostate cancer). Each column contains data from 36 patients. Statistically significant differences (p<0.0001) are indicated by asterisks (*).

Figure 5:

Boxplots representing the mean SWS ratio values in each PCa foci grouped by Gleason Grade group (GG). The number of cancerous regions is indicated for each grade group. No statistically different (p<0.05) relationships were identified between grade groups.

Figure 6:

ROC curves for the SWS mean approach (light blue), the SWS ratio approach (orange), the histogram equalized ARFI (green), and the histogram equalized ARFI ratio (red). Note all ROC curves yield AUCs well above 0.5. The value which maximizes the Youden index for the SWS mean approach is 5.6 m/s, for the SWS ratio approach is 1.11, for the histogram equalized ARFI data is 104, and for the histogram equalized ARFI ratio is 0.94. ROC = receiver operating characteristic; SWS = shear wave speed; Hist. EQ ARFI = histogram equalized acoustic radiation force impulse.

Figure 7:

The mean histogram equalized ARFI values versus the mean SWS values for each prostate region in each patient. SWS = shear wave speed; ARFI Hist. EQ = histogram equalized acoustic radiation force impulse; PZ = peripheral zone; CG = central gland; PCa = prostate cancer.