Integrated Endoscope for Real-Time 3D Ultrasound Imaging and Hyperthermia: Feasibility Study

Abstract

The goal of this research is to determine the feasibility of using a single endoscopic probe for the combined purpose of real-time 3D (RT3D) ultrasound imaging of a target organ and the delivery of ultrasound therapy to facilitate the absorption of compounds for cancer treatment. Recent research in ultrasound therapy has shown that ultrasound-mediated drug delivery improves absorption of treatments for prostate, cervical and esophageal cancer. The ability to combine ultrasound hyperthermia and 3D imaging could improve visualization and targeting of cancerous tissues. In this study, numerical modeling and experimental measurements were developed to determine the feasibility of combined therapy and imaging with a 1cm diameter endoscopic RT3D probe with 504 transmitters and 252 receive channels. This device operates at 5 MHz and has a 6.3 mm × 6.3 mm aperture to produce real time 3D pyramidal scans of 60–120 degrees incorporating 64 × 64 = 4,096 image lines at 30 volumes/sec interleaved with a 3D steerable therapy beam. A finite-element mesh was constructed with over 128,000 elements in LS-DYNA to simulate the induced temperature rise from our transducer with a 3 cm deep focus in tissue. Quarter-symmetry of the transducer was used to reduce mesh size and computation time. Based on intensity values calculated in Field II using the transducer's array geometry, a minimum I _SPTA of 3.6 W/cm² is required from our endoscope probe in order to induce a temperature rise of 4°C within five minutes. Experimental measurements of the array's power output capabilities were conducted using a PVDF hydrophone placed 3 cm away from the face of the transducer in a watertank. Using a PDA14 Signatec data acquisition board to capture full volumes of transmitted ultrasound data, it was determined that the probe can presently maintain intensity values up to 2.4 W/cm² over indefinite times for therapeutic applications combined with intermittent 3D scanning to maintain targeting. These values were acquired using 8 cycle bursts at a prf of 6 kHz. Ex vivo heating experiments of excised pork tissue yielded a maximum temperature rises of 2.3°C over 5 minutes of ultrasound exposure with an average rise of 1.8 ± 0.2°C over 5 trials. Modifications to the power supply and transducer array may enable us to reach the higher intensities required to facilitate drug delivery therapy.

Keywords

3D endoscope hyperthermia imaging ultrasound

Get full access to this article

View all access options for this article.

References

Diederich

Hynynen

. Ultrasound technology for hyperthermia. Ultrasound Med Biol 25, 871–87 (1999).

Meyer

Shin

Kong

, Drug targeting using thermally responsive polymers and local hyperthermia. J Control Release 74, 213–24 (2001).

Liu

. Therapeutic ultrasound: its application in drug delivery. Med Res Rev 22, 204–23 (2002).

Chen

Lin

Kuo

. One-dimensional phased array with mechanical motion for conformal ultrasound hyperthermia. Phys Med Biol 48, 167–82 (2003).

Lin

Fan

Yen

, A theoretical study of cylindrical ultrasound transducers for intracavitary hyperthermia. Int J Radiat Oncol Biol Phys 46, 1329–36 (2000).

Chopra

Bronskill

Foster

. Feasibility of linear arrays for interstitial ultrasound thermal therapy. Med Phys 27, 1281–6 (2000).

Hynynen

. The feasibility of interstitial ultrasound hyperthermia. Med Phys 19, 979–87 (1992).

Smith

Pavy

von Ramm

. High-speed ultrasound volumetric imaging system part I: transducer design and beam steering. IEEE Trans Ultrason Ferroelectr Freq Contr 38, 100–108 (1991).

von Ramm

Smith

Pavy

. High-speed ultrasound volumetric imaging system part II: parallel processing and image display. IEEE Trans Ultrason Ferroelectr Freq Contr 38, 109–115 (1991).

10.

Lee

Suh

. Design and characterization of an intracavitary ultrasound hyperthermia applicator for recurrent or residual lesions in the vaginal cuff. Int J Hyperthermia 19, 563–74 (2003).

11.

Hurwitz

Kaplan

Svensson

, Feasibility and patient tolerance of a novel transrectal ultrasound hyperthermia system for treatment of prostate cancer. Int J Hyperthermia 17, 31–7 (2001).

12.

Sakamoto

Katoh

Shimizu

, Clinical results of treatment of advanced esophageal carcinoma with hyperthermia in combination with chemoradiotherapy. Chest 112, 1487–93 (1997).

13.

Cho

Liu

Cobb

, Ultrasound-induced mild hyperthermia as a novel approach to increase drug uptake in brain microvessel endothelial cells. Pharm Res 19, 1123–9 (2002).

14.

Light

Idriss

Sullivan

, Real-time 3D ultrasonic laparoscopy. Ultrasonic Imaging 27, 89–100 (2005).

15.

Pua

Fronheiser

Noble

, 3-D ultrasound guidance of surgical robotics: a feasibility study. IEEE Trans Ultrason Ferroelectr Freq Control 53, 1999–2008 (2006).

16.

Gentry

Sachedina

Smith

. Catheter ultrasound phased-array transducers for thermal ablation: a feasibility study. Ultrasonic Imaging 27, 89–100 (2005).

17.

Gentry

Smith

. Integrated catheter for 3-D intracardiac echocardiography and ultrasound ablation. IEEE Trans Ultrason Ferroelectr Freq Control 51, 800–8 (2004).

18.

Jensen

Svendsen

. Calculation of pressure pields from arbitrarily shaped, apodized, and excited ultrasound transducers. IEEE Trans Ultrason Ferroelectr Freq Contr 39, 262–267 (1992).

19.

Exposure Criteria for Medical Diagnostic Ultrasound: I Criteria Based on Thermal Mechanisms. 1992, National Council on Radiation Protection and Measurement: Bethesda, MD.

20.

Duck

. Physical Properties of Tissue: a Comprehensive Reference Book (Academic Press, London; San Diego, 1990).

21.

Nyborg

. Solutions of the bio-heat transfer equation. Phys Med Biol 33, 785–92 (1988).

22.

Center for Devices and Radiological Health, 510(k) Guide for Measuring and Reporting Acoustic Output of Diagnostic Ultrasound Medical Devices. 1985, FDA: Rockville, MD.