Modification of intensity distributions from large aperture ultrasound sources

Clarke, Robert L.

doi:10.1016/0301-5629(94)00128-z

Cited by 18 publications

(11 citation statements)

References 25 publications

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“…For example, the requirement for concurrent ultrasonic imaging may call for the removal of a central hole from the power transducer. Predictions of the extent of field perturbation to be expected under such conditions have been made by Clarke [13].…”

Section: D=\aui4mentioning

confidence: 99%

“…In practice, treatment of an extended tumour volume may require the focal point to be scanned over that volume, a process that can negate the desired selectivity unless compensatory cooling of the surrounding tissue occurs, by blood perfusion or otherwise. In this connection there is considerable value in a more general field modelling programme, such as Clarke's [13], which can predict the entire field and not just the focal region.…”

Section: D=\aui4mentioning

confidence: 99%

See 1 more Smart Citation

High intensity focused ultrasound—potential for cancer treatment

Hill¹,

Haar²

1995

The British Journal of Radiology

343

145

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The prospect of being able to use "minimally invasive" surgical techniques is of great interest today, particularly for reasons of health economics, patient acceptability and reduced morbidity. High intensity focused ultrasound (HIFU) has long been known to offer the potential of very precise "trackless lesioning" but has only recently, with the advent of high quality methods of medical imaging, become a practicable possibility. High intensity beams can readily be achieved using either bowel or lens focusing procedures and, by choice of a suitable acoustic frequency, regions of tissue destruction--"lesions"--can be induced at depths of up to at least 10 cm with exposure times of the order of 1 s. Theoretical and experimental evidence indicates that the primary mechanism of damage is thermal, i.e. "cooking" of the tissues. Both conventional cavitation and boiling of tissue water may complicate the situation. Furthermore, substantial non-linear behaviour is involved. On histological appearance the lesions have a spatially sharp demarcation between regions of normal and dead cells. When attempts are made to ablate a block of tissue, by creating an array of adjacent elementary lesions, a phenomenon is observed of inhibition of formation of a lesion whose placing is too close to that of a neighbour. Provided that this problem is dealt with, complete ablation of an extended block of tissue can be achieved. For animal tumours in particular, this observation is reinforced by evidence both of in vitro cell survival and of tumour growth delay experiments. Clinically, the sites accessible for HIFU treatment will be limited by the need for a suitably wide acoustic window that either is available naturally or can be provided by a relatively minor surgical procedure. Tumour sites which thus offer a realistic prospect for local control (and some of which are already the subject of phase 1 trials) include liver, bladder, kidney, prostate, breast and brain. There is also considerable interest in non-cancer applications in these and other sites.

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Section: D=\aui4mentioning

confidence: 99%

Section: D=\aui4mentioning

confidence: 99%

High intensity focused ultrasound—potential for cancer treatment

Hill¹,

Haar²

1995

The British Journal of Radiology

343

145

View full text Add to dashboard Cite

show abstract

“…A 0.5‐mm diameter element GEC‐Marconi polyvinylide fluoride (PVDF) membrane hydrophone (Y‐34‐3598) was used to measure the acoustic pressure profile in three orthogonal directions (one along the sound axis and two perpendicular to the sound axis). For the “truncated circle”–shaped HIFU transducers (43 mm diameter × 21 mm) the focal region, which is determined by the transducer geometry and frequency and thus was similar for all the transducers tested, was found to be ellipsoidal in shape and approximately 10.2 mm × 3.0 mm × 1.4 mm (–6 dB beam width), which compared well with simulated acoustic pressure fields produced using a linear ultrasound propagation model in water (24).…”

Section: Methodsmentioning

confidence: 99%

Design and development of a prototype endocavitary probe for high‐intensity focused ultrasound delivery with integrated magnetic resonance imaging

Wharton

Rivens

Haar

et al. 2007

Magnetic Resonance Imaging

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Purpose: To integrate a high intensity focused ultrasound (HIFU) transducer with an MR receiver coil for endocavitary MR-guided thermal ablation of localized pelvic lesions. Materials and Methods:A hollow semicylindrical probe (diameter 3.2 cm) with a rectangular upper surface (7.2 cm ϫ 3.2 cm) was designed to house a HIFU transducer and enable acoustic contact with an intraluminal wall. The probe was distally rounded to ease endocavitary insertion and was proximally tapered to a 1.5-cm diameter cylindrical handle through which the irrigation tubes (for transducer cooling) and electrical connections were passed. MR compatibility of piezoceramic and piezocomposite transducers was assessed using gradient-echo (GRE) sequences. The radiofrequency (RF) tuning of identical 6.5 cm ϫ 2.5 cm rectangular receiver coils on the upper surface of the probe was adjusted to compensate for the presence of the conductive components of the HIFU transducers. A T1-weighted (T1-W) sliding window dual-echo GRE sequence monitored phase changes in the focal zone of each transducer. High-intensity (2400 W/cm -2 ), short duration (Ͻ1.5 seconds) exposures produced subtherapeutic temperature rises.Results: For T1-W images, signal-to-noise ratio (SNR) improved by 40% as a result of quartering the conductive surface of the piezoceramic transducer. A piezocomposite transducer showed a further 28% improvement. SNRs for an endocavitary coil in the focal plane of the HIFU transducer (4 cm from its face) were three times greater than from a phased body array coil. Local shimming improved uniformity of phase images. Phase changes were detected at subtherapeutic exposures. Conclusion:We combined a HIFU transducer with an MR receiver coil in an endocavitary probe. SNRs were improved by quartering the conductive surface of the piezoceramic. Further improvement was achieved with a piezocomposite transducer. A phase change was seen on MR images during both subtherapeutic and therapeutic HIFU exposures.

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“…Increasing the intensity of the ripple increases the magnitude of the mechanical vibrations and movements of the particles and therefore the magnitude of the received echoes when these are to be processed. The intensity used in medical diagnosis oscillate between 10 and 50 m / 2 , while in therapy, as in the case of diathermy can work in a range of 1 to 3 / 2 There are other uses as cavitation in which the destruction of molecules are intended as in lithotripsy or in nebulization it works with intensities from 10 to 20 / 2 [101] Another magnitude to consider is the speed of ultrasound through a medium; this depends on the density and compressibility of the same, the denser it might be, higher speed of ultrasound will be. [102] Knowing the speed of ultrasound in a medium, one can calculate the depth of reflection points correspond to generate echoes, if it can find the time that it takes to return each echo produced by a change in tissue [103].…”

Section: Characteristic Values Of the Ultrasound Wavesmentioning

confidence: 99%

Ultrasound applications to medicine part i: physical principles.

López

2013

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Modification of intensity distributions from large aperture ultrasound sources

Cited by 18 publications

References 25 publications

High intensity focused ultrasound—potential for cancer treatment

High intensity focused ultrasound—potential for cancer treatment

Design and development of a prototype endocavitary probe for high‐intensity focused ultrasound delivery with integrated magnetic resonance imaging

Ultrasound applications to medicine part i: physical principles.

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