Microwave time delay spectroscopic imagery of isolated canine kidney

A Transmission-Based Dielectric Property Probe for Clinical Applications

We have developed a transmission-based, open-ended coaxial dielectric probe that can be used in clinical situations and overcomes many of the limitations related to the typical reflection-based dielectric probes. The approach utilizes the low profile, open-ended coaxial cables enabling clinicians to still probe relatively compact spaces. The sensing depth can be extended to as large as 1.5 to 2 cm compared with the more typical range of 0.3 mm for conventional probes and is dramatically less affected by measurement technique variability including poor sample contact and cable bending. As a precursor to an actual clinical implementation, we study the technique in a range of homogeneous liquids with substantially varying dielectric properties. The initial results demonstrate good agreement between the transmission-based probe and commercial, reflection-based probes and pave the way for more substantial clinical implementation.

Design and evaluation of a novel breast cancer detection system combining both thermoacoustic (TA) and photoacoustic (PA) tomography

We have developed a novel scanner for breast cancer detection, integrating both thermoacoustic and photoacoustic techniques to achieve dual contrast (microwave and light absorption) imaging. This scanner is nonionizing, low cost, and can potentially provide high-resolution, dual modality three-dimensional images of the breast. The scanner uses front instead of side breast compression and dry instead of gel ultrasonic coupling. Here we present the design of the breast scanner along with initial tissue phantom study results as a precursor to an actual patient study.

Microwave imaging of tissue blood content changes

Active microwave imaging gives information on the dielectric properties of of the body, allowing the collection of data that are distinct from, but complementary to, those available from other imaging methods based on different radiations. Two types of microwave imaging systems have been developed. The first is a planar system that irradiates the object with a plane wave and collects scattered phase and amplitude data at 1024 points on a parallel plane. The data can be reconstructed using a back propagation technique to give an image of the object. The second type of system is a tomographic scanner, consisting of a multiplexed 64-element circular array of waveguides. The waveguides are electronically scanned, alternately as sources and receivers, to give a complete scan of the object with no mechanical movement. A tomographic 'slice' of the object is reconstructed using spectral domain interpolation. Both systems work at 2.45 GHz with an incident power less than 1 mW cm-2 at the object and require a coupling medium (usually water) between the object and the source/receiver. Imaging parameters are appropriate for clinical use: a spatial resolution of 1 cm, measurement time of a few seconds and contrast resolution of around 1%. The effects of changes in perfusion on images of isolated animal organs are presented. Images have also been obtained, with both systems, of the internal dielectric structure of the forearm and of variations in dielectric properties due to changes of tissue blood content effected by application and release of tourniquets to the upper arm. Results show that these changes are well demonstrated by microwave imaging, and possible clinical applications are discussed.

Active microwave computed brain tomography: the response to a challenge

The potential application of active microwave techniques to brain imaging is studied by numerical simulations and experimentally using a recently developed cylindrical microwave scanner. The potential advantages and limitations of this method in static and dynamic brain imaging are presented and compared with other imaging techniques.

Active microwave tomographic imaging of isolated, perfused animal organs

The relative transparency of biological materials to high-frequency electromagnetic waves has encouraged the development of new systems for imaging. This report describes experiments of microwave tomography conducted on a prototype. The object to be analyzed is submerged in water and is illuminated by a plane wave. The total electric field is analyzed by a microwave camera. The recorded data are then processed numerically in order to reconstruct the image that corresponds to the distribution of equivalent currents in a defined plane of a section. Experiments have been conducted on isolated kidneys with and without perfusion. The influence of the perfusing solution temperature has also been studied. These experiments show the potential of this system, especially through the correlation between microwave images and the biological structures. They also confirm previous results concerning spatial resolution and depth of exploration. Finally, the results demonstrate the influence of temperature and support the applicability of this imaging system in non-invasive thermometry, especially for clinical hyperthermia.

Acoustical imaging of a model of a human hand using pulsed microwave irradiation

Pulsed 5.66-GHz microwave energy irradiated a model of a human hand that was positioned above a submerged planar array of 400 hydrophones. Hydrophone response data were analyzed by a computer that graphically reproduced the image.