Nigel Cronin

Microwaves for menorrhagia: a new fast technique for endometrial ablation

Current ablative techniques for treating menorrhagia are unsatisfactory. We tried microwave energy, delivered by an 8 mm diameter probe in the uterine cavity, to treat 23 patients with functional menorrhagia. The mean treatment time was 2 min 12 s (range 50-310 s). 6 months after treatment the success rate is 83%, 13 patients (57%) are amenorrhoeic, and six (26%) are experiencing light menstruation. Three initial failures have been successfully retreated. The technique is safe, and is easier and quicker to perform than current alternatives.

Microwave endometrial ablation: development, clinical trials and outcomes at three years

Objective To describe the introduction of microwave endometrial ablation to clinical practice, and to report the outcomes three years after endometrial ablation.

The histological features of microwave coagulation therapy: an assessment of a new applicator design

Microwave ablation of tumours within the liver may become an adjunct or alternative to resection in patients with primary or secondary cancers. This technique combines the benefits of a large, localized coagulative effect with a single insertion of the applicator, in a significantly shorter time than comparable treatments. A new range of microwave applicators were developed and tested in animal models and both ex‐vivo and in‐vivo specimens of human liver at resection.

Rapid Microwave Ablation of Large Hepatocellular Carcinoma in a High-risk Patient

A 74-year-old male with an inoperable, large (6 cm in diameter) primary hepatocellular carcinoma of the liver was successfully treated using a novel microwave ablating system. Using a single applicator, the tumour was treated at 150 W for 4 minutes. An ablation zone 8 cm in diameter was achieved, which gradually shrunk to form scar tissue that remained unchanged without tumour recurrence for 2 years.

Terahertz Systems: The Demands on Devices

Many potential applications for terahertz technology have been suggested at on time or another. These fall broadly into two categories, those which require the use of terahertz frequencies by their nature and those which are currently being developed at lower frequencies - below 100 GHz, say - but which might benefit from the use of shorter wavelengths were suitable technology available. Prominent among applications in the former category are astronomy and remote sensing. Two examples of satellite radiometer systems currently in the planning stages are master and soprano. The improvements in device technology which would greatly benefit these systems include the provision of a good solid-state local oscillator source capable of delivering at least 1 mW of power. Failing this improvements in the design and efficiency of frequency multipliers would be highly desirable. The development of the SBV may be significant here. As far as the mixer is concerned, apart from reductions in conversion loss and noise temperature improved device mount structures which are more rugged and reproducible than the conventional ‘cats whisker’ mount are urgently needed. If such mounts can be used for device integration so much the better. There are specific applications for one-off scientific instruments for a variety of measurement applications. One example is given of a system designed to measure the scattering from a single-particle scatter. These measurements being in the nature of low frequency scale modelling of infrared scattering. In the millimetre wave region, up to 100 GHz there are several highly commercial applications, in particular high frequency communications and automobile radar. The question is would these be better implemented at higher frequencies were suitable device technology available. The consensus of opinion among works in this field is that there is little advantage in such a move, however, recent advances in the new techniques of micromachining indicate that if, in particular, the source problem could be solved, there may indeed be practical advantages to be gained by the use of shorter wavelengths.

A Microwave Surface Applicator for Tissue Coagulation: Technical Characteristics and Performances

This work describes the mechanical and the electromagnetic design of a microwave surface applicator used to coagulate liver tissue in the treatment of hepatic tumors. A good prediction of the ratio between reflected and forward microwave power (return loss) is obtained with a finite element model using commercial software. Laboratory testing of the applicator performed in polyacrylamide gel (PAG) and in ex vivo bovine liver show a hemispherical heat distribution pattern and hemispherical ablations up to 20 mm in diameter and 15 mm in depth in a controlled manner in 1 min. The applicator can also be used to coagulate larger areas of tissue with 2–5 mm depth by moving the applicator on the surface of the tissue. Experimental results indicate that the coagulated volume of tissue is approximately proportional to the energy delivered into ex vivo bovine liver, hemispherical in shape, obtained in short time duration with a volumetric rate of coagulated tissue of about 50 mm3 /s.

Comparison of measured and computed conversion loss from a resonant tunneling device multiplier

The behavior of a resonant tunneling device (RTD) as a multiplier over a range of bias voltage is investigated. The experimental results agree well with large-signal simulations based on a simple equivalent circuit with element values derived from the I-V characteristic and low-frequency small-signal impedance measurements. This technique can be extended to assist in the design and realization of millimeter and submillimeter RTD multipliers.<<ETX>>

Determination and reduction of the capacitance associated with the bonding pads of planar millimeter-wave mixer diodes

A calculation of the capacitance associated with the metal bonding pads of a planar millimeter-wavelength mixer diode is presented. This capacitance is the largest component associated with such a device, contributing a calculated 22 fF toward a total diode capacitance of 30 fF. A demonstration of how the pad capacitance can be almost halved by incorporating an air bridge into the diode structure is included. Computer simulations show that this additional processing step can cause a 1.2-dB drop in mixer conversion loss at 94 GHz.<<ETX>>

Computer modeling of electromagnetic and thermal effects in microwave soft tissue ablation (Invited Paper)

Microwave Endometrial Ablation (MEA) is a technique that can be used for the treatment of abnormal uterine bleeding. The procedure involves sweeping a specially designed microwave applicator throughout the uterine cavity to achieve an ideally uniform depth of tissue necrosis of between 5 and 6mm. We have performed a computer analysis of the MEA procedure in which finite element analysis was used to determine the SAR pattern around the applicator. This was followed by a Green Function based solution of the Bioheat equation to determine the resulting induced temperatures. The method developed is applicable to situations involving a moving microwave source, as used in MEA. The validity of the simulation was verified by measurements in a tissue phantom material using a purpose built applicator and a calibrated pulling device. From the calculated temperatures the depth of necrosis was assessed through integration of the resulting rates of cell death estimated using the Arrhenius equation. The Arrhenius parameters used were derived from published data on BHK cells. Good agreement was seen between the calculated depths of cell necrosis and those found in human in-vivo testing.

Microwave soft tissue ablation (Invited Paper)

Microsulis, in conjunction with the University of Bath have developed a set of novel microwave applicators for the ablation of soft tissues. These interstitial applicators have been designed for use in open surgical, laparoscopic and percutaneous settings and range in diameter from 2.4 to 7 mm. A 20 mm diameter flat faced interface applicator was developed as an adjunct to the open surgical interstitial applicator and has been applied to the treatment of surface breaking lesions in hepatobiliary surgery. Taken as a complete tool set the applicators are capable of treating a wide range of conditions in a safe and efficacious manner. The modality employs a radiated electromagnetic field at the allocated medical frequency of 2.45 GHz and powers between 30 and 150 Watts. Computer simulations, bench testing, safety and efficacy testing, ex-vivo and in-vivo work plus clinical trials have demonstrated that these systems are capable of generating large volumes of ablation in short times with favourable ablation geometries. Clinical studies have shown very low complication rates with minimal local recurrence. It is considered that this modality offers major advantages over currently marketed products. The technique is considered to be particularly safe as it is quick and there is no passage of current obviating the requirement for grounding pads. Since the microwave field operates primarily on water and all soft tissues with the exception of fat are made up of approximately 70% water the heating pattern is highly predictable making repeatability a key factor for this modality.