Sarah Kathryn Patch PhD, Presenter: Nothing to Disclose

David Hull MD, Abstract Co-Author: Nothing to Disclose

Majorca Thomas, Abstract Co-Author: Nothing to Disclose

Stephanie Griep, Abstract Co-Author: Nothing to Disclose

Kenneth Jacobsohn MD, Abstract Co-Author: Nothing to Disclose

William See MD, Abstract Co-Author: Nothing to Disclose

If results of a larger study also support the hypothesis that the contrast mechanism is sensitive to cancer then development of a clinical prototype for in vivo imaging will be warranted.

Prostate cancer is a good application for thermoacoustic imaging for several reasons. Mechanical properties of healthy and cancerous prostate tissue are well matched, so the assumption of constant sound speed is accurate. Measurements represent integrals of the thermoacoustic source term over spheres centered at the transducer focus. Signal production by very high frequency irradiation is proportional to ionic content, and ionic content of prostatic fluids produced by healthy tissue in the peripheral zone is approximately three times higher than in blood and plasma whereas cancer suppresses ionic content. Signal strength is therefore expected to decrease with extent of cancerous involvement.

To test this hypothesis we imaged fresh human prostate specimens ex vivo and compared to the gold standard, histology. Over two-dozen specimens were imaged immediately after radical prostatectomy performed as part of normal care. Irradiation pulses with carrier frequency 108 MHz ensured excellent electromagnetic depth penetration. 700 ns pulses with power exceeding 20 kW propagated 20-25 mJ into a benchtop imaging system. 2.25 MHz focused single element transducers received the thermoacoustic pulses, which were amplified by 54 dB and signal averaged 64 times before recording to disc. Spatial encoding was performed in step-and-shoot mode, with 1.8-degree rotations between views and 3 mm translation between acquisition slices. Approximately 20 slices were acquired per specimen. Reconstruction was performed by filtered backprojection after extensive preprocessing. The peripheral zone was subdivided into regions of interest corresponding to tissue type (Gleason grade, HGPin, inflammation, etc), as annotated on histology slides from three cases.  

Reconstructions revealed some common features: the verumontanum and urethra are frequently visualized.   Mean reconstruction values in cancer-free regions were four times greater than in regions with high percentage of cancer.

Patch, S, Hull, D, Thomas, M, Griep, S, Jacobsohn, K, See, W, Thermoacoustic Imaging of Fresh Prostate Specimens – Preliminary Comparison to Histology.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14004000.html