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Chopra, Rajiv; Luginbuhl, C.; Weymouth, Alfred J.; Foster, F. Stuart; Bronskill, Michael

doi:10.1088/0031-9155/46/12/305

Cited by 44 publications

(6 citation statements)

References 37 publications

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“…Directional heating can be realized through the use of sectored cylindrical, 21 curvilinear, 22 or planar transducers. 23,24 Multielement transducer configurations can be utilized to adjust the energy distribution along the length of the heating applicator. 25,26 Multifrequency transducers can be used to adjust the radial distance of energy deposition from each transducer.…”

Section: Introductionmentioning

confidence: 99%

“…25,26 Multifrequency transducers can be used to adjust the radial distance of energy deposition from each transducer. 27 These transducer designs enable the generation of intricate thermal damage patterns in three dimensions, 22,23,28,29 which can be important in reducing some of the side effects common in other forms of therapy for prostate cancer. 4 Equally important is the capability to monitor the heating pattern produced during treatment.…”

Section: Introductionmentioning

confidence: 99%

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MRI‐compatible transurethral ultrasound system for the treatment of localized prostate cancer using rotational control

et al. 2008

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Magnetic resonance imaging (MRI)-guided transurethral ultrasound therapy is a potential minimally invasive treatment for localized prostate cancer offering precise targeting of tissue within the gland, short treatment times, and the capability to quantify the spatial heating pattern delivered during therapy. A significant challenge in MRI-guided ultrasound therapy is the design and construction of MRI-compatible equipment capable of operation in a closed-bore MR imager. We describe a prototype system developed for MRI-guided transurethral ultrasound therapy and characterize the performance of the different components including the heating applicator design, rotational motor, and radio frequency electronics. The ultrasound heating applicator described in this study incorporates a planar transducer and is capable of producing high intensity ultrasound energy in a localized region of tissue. Results demonstrated that the heating applicator exhibits excellent MRI-compatibility, enabling precise MR temperature measurements to be acquired as close as 6 mm from the device. Simultaneous imaging and rotational motion was also possible during treatment using a motor based on piezoelectric actuators. Heating experiments performed in both phantoms and in a canine model with the prototype system verified the capability to perform simultaneous MR imaging and therapy delivery with this system. Real-time control over therapy using MR temperature measurements acquired during heating can be implemented to achieve precise patterns of thermal damage within the prostate gland. The technical feasibility of using the system developed in this study for MRI-guided transurethral ultrasound therapy in a closed-bore MR imager has been demonstrated.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

MRI‐compatible transurethral ultrasound system for the treatment of localized prostate cancer using rotational control

et al. 2008

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“…Control over the spatial deposition of energy can be achieved with some ultrasoundbased transurethral heating applicators. Directional heating can be realized through the use of sectored cylindrical transducers (Diederich et al 2000) or planar transducers (Chopra et al 2001, Lafon et al 1998. Multi-element transducer configurations can be utilized to adjust the energy distribution along the length of the heating applicator (Diederich and Burdette 1996).…”

Section: Introductionmentioning

confidence: 99%

“…Multi-frequency transducers can enable greater control over the radial energy deposition from each transducer (Chopra et al 2003). These transducer designs enable the generation of intricate thermal damage patterns in three dimensions (Chopra et al 2001, Tyreus et al 2003 which is particularly important in avoiding the side effects common in other forms of therapy for prostate cancer (Potosky et al 2004).…”

Section: Introductionmentioning

confidence: 99%

Analysis of factors important for transurethral ultrasound prostate heating using MR temperature feedback

Chopra¹,

Wachsmuth²,

Burtnyk³

et al. 2006

Phys. Med. Biol.

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The feasibility of using MR thermometry for temperature feedback to control a transurethral ultrasound heating applicator with planar transducers was investigated. The sensitivity of a temperature-based feedback algorithm to spatial (control point area, slice thickness, angular alignment) and non-spatial (imaging time, temperature uncertainty) parameters was evaluated through numerical simulations. The angular alignment of the control point with the ultrasound beam was an important parameter affecting the average spatial error in heat delivery. The other spatial parameters were less influential, thus providing an opportunity to reduce spatial resolution for increased SNR in the MR imaging. The update time was the most important non-spatial parameter determining the performance of the control algorithm. Combined non-spatial and spatial parameters achieved acceptable performance with a voxel size of 3 mm x 3 mm, a 10 mm slice thickness and a 5 s update time. Temperature uncertainty of up to 2 degrees C had little effect on the performance of the control algorithm but did reduce the average error slightly due to a systematic, noise-induced overestimation of the boundary temperature. These simulations imply that MR thermometry performed on clinical 1.5 T imaging systems is of sufficient quality for use as thermal feedback for conformal prostate thermal therapy with transurethral ultrasound heating applicators incorporating planar transducers.

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“…Deardorff et al (1998) produced large lesions approximately 30 mm in diameter (measured perpendicular to transducer axis), using a single-element cylindrical ultrasound transducer (2.5 mm od and 10 mm length, 7.2 MHz resonant frequency). Chopra et al (2001) showed that a single-element scanned planar transducer (3 mm × 15 mm) produced thermal lesions in excised bovine liver tissue with a maximum diameter of 36 mm at 4.7 MHz, also measured perpendicular to the axis of the transducer. These ultrasound-generated lesions are considered large in comparison to those produced by other single, interstitial thermal therapy applicators such as lasers and microwave antennae, but are smaller than the lesions produced by our helical coils.…”

Section: Discussionmentioning

confidence: 99%

The use of a dispersive ground electrode with a loosely wound helical coil for interstitial radiofrequency thermal therapy

McCann¹,

Sherar²

2006

Phys. Med. Biol.

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We have developed a novel, thermal therapy device designed to improve local control of large solid tumours using heat in the range 55-90 degrees C. The device is a helical coil designed to be loosely wound inside a tumour and excited with radiofrequency energy at 27.12 MHz. This design exploits the size and uniformity of the electric fields generated by magnetic induction inside this solenoidal geometry for heating and coagulating a large target volume. The use of the electrically conductive shape memory alloy Nitinol for the coil and an external ground plane permit the minimally invasive percutaneous insertion of the coil through a single cannulating delivery needle. To demonstrate the feasibility of this device, phantom models and finite-element models using COMSOL 3.2 were used to characterize uniformity of the radial and axial ARD (absorption rate density) profiles of different monopolar coil geometries. COMSOL 3.2 was also used to calculate temperature profiles and distributions produced by these coils in a non-perfused tissue-mimicking domain following a 10 min heating period. ARD results showed that optimum radial and axial uniformities were achieved with a 0.75 cm pitch and 3 cm length for a 1.5 cm diameter coil, and a 1.4 cm pitch and 4.2 cm length for a 2 cm diameter coil. These coils were able to produce lesions in excised bovine liver of 4 cm x 4.5 cm and 3.5 cm x 6.5 cm, respectively. Predicted temperature profiles showed similar profile sizes and shapes in a non-perfused domain, with the absolute temperature rise determined by the source input to the coil. These results demonstrate the potential of this interstitial, monopolar induction coil device for heating large tumours using a single applicator delivered through a single needle insertion.

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Cited by 44 publications

References 37 publications

MRI‐compatible transurethral ultrasound system for the treatment of localized prostate cancer using rotational control

MRI‐compatible transurethral ultrasound system for the treatment of localized prostate cancer using rotational control

Analysis of factors important for transurethral ultrasound prostate heating using MR temperature feedback

The use of a dispersive ground electrode with a loosely wound helical coil for interstitial radiofrequency thermal therapy

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