title: Quantitative ultrasound imaging for monitoring in situ high-intensity focused ultrasound exposure.
abstract: Quantitative ultrasound (QUS) imaging is hypothesized to map temperature elevations induced in tissue with high spatial and temporal resolution. To test this hypothesis, QUS techniques were examined to monitor high-intensity focused ultrasound (HIFU) exposure of tissue. In situ experiments were conducted on mammary adenocarcinoma tumors grown in rats and lesions were formed using a HIFU system. A thermocouple was inserted into the tumor to provide estimates of temperature at one location. Backscattered time-domain waveforms from the tissue during exposure were recorded using a clinical ultrasonic imaging system. Backscatter coefficients were estimated using a reference phantom technique. Two parameters were estimated from the backscatter coefficient (effective scatterer diameter (ESD) and effective acoustic concentration (EAC). The changes in the average parameters in the regions corresponding to the HIFU focus over time were correlated to the temperature readings from the thermocouple. The changes in the EAC parameter were consistently correlated to temperature during both heating and cooling of the tumors. The changes in the ESD did not have a consistent trend with temperature. The mean ESD and EAC before exposure were 120 ± 16 μm and 32 ± 3 dB/cm3, respectively, and changed to 144 ± 9 μm and 51 ± 7 dB/cm3, respectively, just before the last HIFU pulse was delivered to the tissue. After the tissue cooled down to 37 °C, the mean ESD and EAC were 126 ± 8 μm and 35 ± 4 dB/cm3, respectively. Peak temperature in the range of 50-60 °C was recorded by a thermocouple placed just behind the tumor. These results suggest that QUS techniques have the potential to be used for non-invasive monitoring of HIFU exposure.
authors: Acoustic MedSystems Inc., Savoy, IL, USA Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
authors: Goutam
authors: G
authors: Ghoshal
authors: Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
authors: Jeremy P
authors: JP
authors: Kemmerer
authors: Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
authors: Chandra
authors: C
authors: Karunakaran
authors: Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
authors: Rami
authors: R
authors: Abuhabsah
authors: Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
authors: Rita J
authors: RJ
authors: Miller
authors: Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
authors: Sandhya
authors: S
authors: Sarwate
authors: Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA oelze@illinois.edu.
authors: Michael L
authors: ML
authors: Oelze
mesh_terms: D000230:Adenocarcinoma / Q000000981:diagnostic imaging* / Q000601:surgery*; D000818:Animals; D045744:Cell Line, Tumor; D004867:Equipment Design; D005260:Female; D057086:High-Intensity Focused Ultrasound Ablation / Q000295:instrumentation*; D008325:Mammary Neoplasms, Experimental / Q000000981:diagnostic imaging* / Q000601:surgery*; D051381:Rats; D011916:Rats, Inbred F344; D014463:Ultrasonography
keywords: HIFU; effective scatterer concentration; effective scatterer diameter; parametric imaging; quantitative ultrasound imaging