Ultrasonic Measurement Techniques and Equipment Output Levels

Stewart, Harold F.

doi:10.1007/978-1-4612-5805-6_3

Cited by 54 publications

(19 citation statements)

References 35 publications

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“…In other experiments that use phantoms, the drift during the image acquisition was measured to be within 20.01 ppm/h. The drift would be less than 0.0002 ppm for the image acquisition within 1 min.…”

Section: Discussionmentioning

confidence: 99%

Optimization of spoiled gradient‐echo phase imaging for in vivo localization of a focused ultrasound beam

Chung

Hynynen

Colucci

et al. 1996

Magnetic Resonance in Med

195

149

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The parameters of a spoiled gradient-echo (SPGR) pulse sequence have been optimized for in vivo localization of a focused ultrasound beam. Temperature elevation was measured by using the proton resonance frequency shift technique, and the phase difference signal-to-noise ratio (SNR delta phi) was estimated in skeletal muscle and kidney cortex in 10 rabbits. Optimized parameters included the echo time equivalent to T2* of the tissue, the longest repetition time possible with a 20-s sonication, and the flip angle equivalent to the Ernst angle. Optimal SPGR phase imaging can detect a sonication beam with a peak phase difference of 0.55 radian, which corresponds to a temperature elevation of 7.3 degrees C. The sonication beam can be localized within one voxel (0.6 x 0.6 x 5 mm3) at power levels that are below the threshold for thermal damage of the tissue.

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Section: Discussionmentioning

confidence: 99%

Optimization of spoiled gradient‐echo phase imaging for in vivo localization of a focused ultrasound beam

Chung

Hynynen

Colucci

et al. 1996

Magnetic Resonance in Med

195

149

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“…23 The value of R ͑isodose constant͒, which is temperature dependent, was chosen based on experimental data: 5 Rϭ0.5 for temperatures above 43°C and Rϭ0. 25 for temperatures below 43°C. The boundary of an isothermal dose value of 240 min at the reference temperature of 43°C was selected to predict the size of the necrosed tissue volume in muscle.…”

Section: A Simulation Of the Focused Ultrasound Beammentioning

confidence: 99%

Thermal dosimetry of a focused ultrasound beam in vivo by magnetic resonance imaging

1999

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Magnetic resonance imaging (MRI) thermometry has been utilized for in vivo evaluation of thermal exposure induced by a focused ultrasound beam. A simulation study of the focused ultrasound beam was conducted to select imaging parameters for reducing the error due to the spatial and temporal averaging of MRI. Temperature imaging based on the proton resonance frequency shift was utilized to obtain the temperature distribution during sonication in the skeletal muscle of eight rabbits. MRI-derived temperature information was then used to calculate the thermal dose distribution induced by the sonication and to estimate the coagulated tissue volume. The tissue changes were also evaluated directly by taking the T2-weighted and the contrast agent enhanced T1-weighted MR images. Errors in the temperature and thermal dose measurements were found to be minimal using the following parameters: slice thickness = 3 mm, voxel dimension = 0.6 mm, and scan time per image = 3.4 s. The estimated dimensions of the coagulated tissue volume were in good agreement with the tissue damages seen on the contrast agent enhanced T1-weighted images. The tissue damage seen on the histology was closely matched to the ones seen on the T2-weighted images. This study showed that MRI thermometry has significant potential for both monitoring the thermal exposure and evaluating the tissue damage. This would allow real-time control of the sonication parameters to optimize clinical treatments.

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“…The weight changes on the target due to the ultrasound radiation force were recorded by the HP9836 computer via the IEEE-488 interface. The warming of the target and the convergence of the beam were estimated and taken into account in the program that calculated the total acoustical power from the measurements [10]. At high output powers, low duty cycles were used in order to reduce water streaming.…”

Section: Generation Of Ultrasoundmentioning

confidence: 99%

A scanned, focused, multiple transducer ultrasonic system for localized hyperthermia treatments

Hynynen¹,

Roemer²,

Anhalt

et al. 2010

International Journal of Hyperthermia

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A commercial diagnostic ultrasound scanner (Octoson) was modified for performing hyperthermia treatments. The temperature elevations were induced in tissues by four large, focused ultrasonic transducers whose common focal zone was scanned along a computer controlled path as determined from B-scan images. The system is described and the results of preliminary tests demonstrating some of its capabilities are given. Extensive tests with canine thighs and kidneys were performed. The blood flow to the kidneys was controllable, and thus tumours having different blood perfusion rates could be simulated. The results showed that the system is capable of inducing a local temperature maximum deep in tissues (up to 10 cm was tested) and that tissues with high perfusion rates could be heated.

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Ultrasonic Measurement Techniques and Equipment Output Levels

Cited by 54 publications

References 35 publications

Optimization of spoiled gradient‐echo phase imaging for in vivo localization of a focused ultrasound beam

Optimization of spoiled gradient‐echo phase imaging for in vivo localization of a focused ultrasound beam

Thermal dosimetry of a focused ultrasound beam in vivo by magnetic resonance imaging

A scanned, focused, multiple transducer ultrasonic system for localized hyperthermia treatments

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