Biomedical subjects

Claire McCann

Publications and source records attributed to Claire McCann.

6 recordsLinked to original sources

PubMed2006

Development of a novel loosely wound helical coil for interstitial radiofrequency thermal therapy.

We have developed a novel, radiofrequency 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 solenoid or helical coil designed to be loosely wound inside a tumour and excited with radiofrequency energy. Typically, we associate a uniform axially directed magnetic field with a solenoid coil, which when time varying, results in an electric field inside the coil, which lies mainly in the circumferential direction. In addition to this magnetically induced electric field, there exists a less familiar axially directed electric field inside the coil. Previous investigators have demonstrated the presence of this secondary axial electric field both experimentally and theoretically. Our design exploits the size and uniformity of these electric fields, for heating and coagulating a large tissue volume with a single applicator. The loosely wound solenoid is constructed from Nitinol, an electrically conductive shape memory alloy that permits the minimally invasive percutaneous insertion of the coil through a single cannulating delivery needle. To demonstrate the potential of this device and to determine the optimal frequency of operation, phantom tissue models and finite-element calculation models using COMSOL 3.2 were used to characterize frequency- and geometry-dependent trends in absorption rate density (ARD), which is proportional to electric field intensity. Radial and axial ARD profiles were measured, calculated and evaluated to determine the frequency and geometry best suited for producing large, homogenous coagulation volumes. Based on the trade-off between radial and axial uniformities of the ARD profiles, a 2 cm diameter coil with a 4 cm length and 1 cm pitch, operated at 27.12 MHz, produced the optimal heating pattern, as determined using tissue-mimicking phantom models.

Alloys↗

PubMed2006

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

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.

Alloys↗

PubMed2004

Comparative evaluation of image quality from three CT simulation scanners.

Today, radiation therapy (RT) is moving toward increased radiation dose to the tumor as a result of 3D conformal RT (3DCRT) and intensity-modulated RT (IMRT), which have been made possible by advances in volumetric-based image planning with digital imaging systems such as computed tomography (CT). Treatment planning for such RT requires superior CT image quality. Our goal in this study was to evaluate and to compare the image quality of three unique CT simulation scanners available at our center for both single- and multiple-slice helical scanners. These scanners included a conventional 70-cm bore single-slice scanner (Philips Medical Systems), a large 85-cm bore single-slice scanner (Philips Medical Systems), and a 70-cm bore multislice scanner (GE Medical Systems). Image quality was evaluated in terms of image noise, low-contrast detectability (LCD), limiting spatial resolution (modulation transfer function), and slice thickness accuracy in accordance with guidelines set out by the AAPM. A commercially available Catphan phantom was used to characterize image quality for both axial and helical modes of scanning. We found that image quality was generally comparable for all scanners. Limiting spatial resolution and slice thickness accuracy were comparable for all three scanners for both scanning modes. The multislice unit was superior in terms of noise content, resulting in improved visualization of small, low-contrast objects, which is of significant clinical importance, particularly for soft tissue delineation. In addition, the multislice unit optimizes volume coverage speed and longitudinal resolution without compromising image quality, a significant advantage for the radiation oncology environment.

Equipment Design↗

PubMed2003

Feasibility of salvage interstitial microwave thermal therapy for prostate carcinoma following failed brachytherapy: studies in a tissue equivalent phantom.

Thermal therapy is an experimental treatment to destroy solid tumours by heating them to temperatures ranging from 55 degrees C to 90 degrees C, inducing thermal coagulation and necrosis of the tumour. We are investigating the feasibility of interstitial microwave thermal therapy as a salvage treatment for prostate cancer patients with local recurrence following failed brachytherapy. Due to the electrical and thermal conductivity of the brachytherapy seeds, we hypothesized that the seeds could scatter the microwave energy and cause unpredictable heating. To investigate this, a 915 MHz helical antenna was inserted into a muscle-equivalent phantom with and without brachytherapy seeds. Following a 10 W, 5 s input to the antenna, the temperature rise was used to calculate absorbed power, also referred to as specific absorption rate (SAR). Plane wave models based on Maxwell's equations were also used to characterize the electromagnetic scattering effect of the seeds. In addition, the phantom was heated with 8 W for 5 min to quantify the effect of the seeds on the temperature distribution during extended heating. SAR measurements indicated that the seeds had no significant effect on the shape and size of the SAR pattern of the antenna. However, the plane wave simulations indicated that the seeds could scatter the microwave energy resulting in hot spots at the seed edges. Lack of experimental evidence of these hot spots was probably due to the complex polarization of the microwaves emitted by the helical antenna. Extended heating experiments also demonstrated that the seeds had no significant effect on the temperature distributions and rates of temperature rise measured in the phantom. The results indicate that brachytherapy seeds are not a technical impediment to interstitial microwave thermal therapy as a salvage treatment following failed brachytherapy.

Brachytherapy↗

PubMed2003

The transition to parenthood among young African American and Latino couples: relational predictors of risk for parental dysfunction.

This study examined relationship factors associated with parental dysfunction among young African American and Latino couples. Parent dysfunction was defined in terms of parenting stress, child abuse potential, physically punitive behavior, and paternal disengagement. Fathers who reported positive relations with their own parents and partners before childbirth reported more positive adjustments to parenthood at follow-up. The quality of the prebirth partner relationship buffered the impact of a relationship breakup on a young father's adjustment to parenthood. The quality of a mother's relationship with her parents was the best predictor of her adjustment to parenthood. However, mothers who reported large declines in the quality of the partner relationship also reported high levels of parenting stress. Clinical and policy implications of findings are discussed.

Adaptation, Psychological↗

PubMed2003

Interstitial microwave thermal therapy for prostate cancer.

Thermal therapy is used to kill tumors by heating them to temperatures >50 degrees C for an extended period of time. Cell death results from thermal coagulation. The energy sources available for this approach include radiofrequency electrodes, microwave antennas, laser fiberoptics, and ultrasound transducers. Each of these modalities has the potential to be delivered in a minimally invasive manner, and many theoretical and experimental investigations of these devices have been performed. This review describes current knowledge of interstitial microwave thermal therapy for prostate cancer. Examples are given from an ongoing trial in patients who have recurrent or persistent disease following radiation therapy. Future directions for pretreatment planning and real-time monitoring and control are discussed. These techniques have the potential to optimize treatments on a patient-specific basis and will be instrumental in planned future trials of this therapy as first line for prostate cancer.

Animals↗