High Frequency Reflex Transmission Imaging: Feasibility for Eventual Application to the Diagnosis of Skin Tumours

Summary and Discussion

Reflex Transmission Imaging (RTI) has been implemented in order to map the relative attenuation characteristics of the skin surface. Phantoms made of a homogeneous backscattering gelatin material, containing surface attenuating discs of varying thickness, were used to evaluate image quality by measuring contrast-to-speckle ratio and plotting contrast-detail curves. Using these phantoms it was shown that of two transducers evaluated for RTI, a 20 MHz poorly focused transducer provided images of better quality than a 15 MHz. well-focused transducer, due to its better sensitivity.

Attenuating discs as small as 1 mm in diameter in the phantom were clearly visible with this experimental RTI skin imaging system and a preliminary RTI skin image that was obtained in vitro clearly visualised an attenuating benign tumour against surrounding healthy tissue. Further work will aim to optimise high frequency RTI and assess its usefulness for skin tumour diagnosis.

A preliminary contrast detail phantom for RTI, constructed from surface attenuating discs, proved to provide a successful method for assessing relative image quality. However, the limits of spatial resolution for both transducers could not be explored using attenuating discs because diameters smaller than 1 mm were not available due to construction difficulties. This restriction has since been circumvented using a phantom constructed from surface attenuating triangles that can provide linear object dimensions of hundreds of microns, which will be reported in a future paper.