Ultrasonic Hyperthermia for Ophthalmic Therapy

Lizzi, Frederic L.; Coleman, D. Jackson; Driller, J.; Ostromogilsky, M.; Chang, Stanley; Greenall, P.

doi:10.1109/t-su.1984.31532

Cited by 59 publications

(20 citation statements)

References 9 publications

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“…Our initial model was applicable to thin tissue layers. Computed results were found to be in excellent agreement with measured temperatures and lesion sizes in the sclera and chorioretinal complex [15], Our tumor model extends these earlier results. The current model [16] assumes linear acoustic propagation, temperature-independent tissue properties and spatially uniform thermal constants and perfusion.…”

Section: Theoretical Model Of Small Ablative Lesionssupporting

confidence: 85%

“…Our simulations indicate how several factors interact with ablation lesion production [15,16]. For very short exposures (less than about 0.5 s in the above case), the temperature rises are linearly related to the in situ inten sity (which closely resembles the incident beam), the absorption coefficient and time.…”

Section: Beam Damage Integralmentioning

confidence: 71%

“…The follow ing paragraphs illustrate how we have employed these strategies for specific ablative ocular treatments that re with our recent model results. Another application requir ing very small lesions involves retinal tear confinements; for the above transducer, we found that suitable lesion diameters (less than 0.5 mm) could be produced by 0.25-second exposures at spatial average, focused intensities of 1 kW/cm2 [15].…”

Section: Illustrative Experimental and Clinical Datamentioning

confidence: 91%

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High-Precision Thermotherapy for Small Lesions

Lizzi

1993

Eur Urol

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Section: Theoretical Model Of Small Ablative Lesionssupporting

confidence: 85%

Section: Beam Damage Integralmentioning

confidence: 71%

Section: Illustrative Experimental and Clinical Datamentioning

confidence: 91%

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High-Precision Thermotherapy for Small Lesions

Lizzi

1993

Eur Urol

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“…It was shown that at two different ultrasonic frequencies, 3 and 4 MHz, identical constant volume curves resulted even though there were two different threshold levels (Dunn and Fry, 1971). Later, a damage integral was defined to predict the occurrence and dimensions of thermally induced ophthalmic lesions (Lizzi et al, 1984).…”

Section: Dosimetrymentioning

confidence: 99%

Ultrasound–biophysics mechanisms

O’Brien

2007

Progress in Biophysics and Molecular Biology

596

416

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Ultrasonic biophysics is the study of mechanisms responsible for how ultrasound and biological materials interact. Ultrasound-induced bioeffect or risk studies focus on issues related to the effects of ultrasound on biological materials. On the other hand, when biological materials affect the ultrasonic wave, this can be viewed as the basis for diagnostic ultrasound. Thus, an understanding of the interaction of ultrasound with tissue provides the scientific basis for image production and risk assessment. Relative to the bioeffect or risk studies, that is, the biophysical mechanisms by which ultrasound affects biological materials, ultrasound-induced bioeffects are generally separated into thermal and nonthermal mechanisms. Ultrasonic dosimetry is concerned with the quantitative determination of ultrasonic energy interaction with biological materials. Whenever ultrasonic energy is propagated into an attenuating material such as tissue, the amplitude of the wave decreases with distance. This attenuation is due to either absorption or scattering. Absorption is a mechanism that represents that portion of ultrasonic wave that is converted into heat, and scattering can be thought of as that portion of the wave, which changes direction. Because the medium can absorb energy to produce heat, a temperature rise may occur as long as the rate of heat production is greater than the rate of heat removal. Current interest with thermally mediated ultrasound-induced bioeffects has focused on the thermal isoeffect concept. The non-thermal mechanism that has received the most attention is acoustically generated cavitation wherein ultrasonic energy by cavitation bubbles is concentrated. Acoustic cavitation, in a broad sense, refers to ultrasonically induced bubble activity occurring in a biological material that contains pre-existing gaseous inclusions. Cavitation-related mechanisms include radiation force, microstreaming, shock waves, free radicals, microjets and strain. It is more challenging to deduce the causes of mechanical effects in tissues that do not contain gas bodies. These ultrasonic biophysics mechanisms will be discussed in the context of diagnostic ultrasound exposure risk concerns.

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“…Ultrasound has become a leading method for realizing such procedures, due to its ability to accurately focus energy into the body in order to heat and destroy small volumes of tissue. A wide range of treatments have been investigated to treat tumors, to ablate the prostate for benign hyperplasia (BHP) [1][2][3], to control bleeding [4], for cardiac treatments [5], to treat various eye conditions [6], and to treat brain disorders [7]. An increasing number of clinical treatments and trials are being conducted worldwide for tumor ablation in various organs, while exciting prospects for enhancing and expanding present therapies are underway.…”

Section: Introductionmentioning

confidence: 99%