Ultrasound

Ultrasound is one of the earliest modalities applied for human imaging and has been used in many different fields.  This technology is based on penetration characteristics of a certain medium of interest (human organs in this case) and measurement of the reflection signals. The reflected signal can reveal details about the anatomy of the medium according to its echogenecity. Advantages of ultrasound include its portability,ease of use, low cost, lack of radiation leading to broad application of this modality.

Although conventional ultrasound can provide 3D images, the most well known ultrasound images are acquired in B mode, which represent 2D image reconstruction. The resolution of ultrasound increases with higher frequencies at the cost of decreasing tissue penetration. Although this is a limitation in internal organ imaging, this would be an advantage in diagnostic imaging of the skin. The frequency of current ultrasound transducers available for diagnostic purpose ranges from 7 to 20 MHz. On the research front, ultrasound probes of up to 75 to 100 MHz are used for animal imaging. A higher frequency ultrasound could be potentially applied to image the skin with the capability to reach depths of 2 to 5mm.

Characterization of skin lesion

Conventional ultrasound has been applied to characteritze benign and malignant lesions. Based on specific ultrasonic patterns and echogenecity of various lesions, ultrasound has been shown to be superior to palpation in diagnosis of subepidemal lesions including lipomas, epidermal cyst, and ganglionic cyst. With the additional information obtained using Doppler phenomenon, ultrasound can also be beneficial in characterizing vascular lesions. Overall, ultrasound technology, even in its current state, can increase diagnostic accuracy if applied in the right setting.

Skin lesion response to therapy

In literature, there is evidence that ultrasound characterization of lesions can be used to assess response to treatment on follow up studies.

Pre-surgical evaluation for malignant and benign lesions

Ultrasound can evaluate the size, shape, and depth the lesion (in concordance with the resolution of the particular ultrasound machine being used). In addition, the relationship of the lesions to adjacent vessels and structures can be assessed preoperatively.

In inflammatory lesions, such as Hidradenitis Suppurtiva, it has been reported that ultrasound characteristics including echolucent areas and degree of dilated follicles can help evaluate the degree of disease involvement. An accurate assessment of skin involvement is important prior to surgery because complete excision needed in order to prevent recurrence.

Future Directions

As a physics fact, as the frequencies of ultrasound waves increases, the penetration into the tissue decreases consequently. However, given the unique superficial location of the skin and subcutaneous lesions, higher resolution can be achieved through increasing the frequency of ultrasonic waves with less concern about the depth of penetration. A future direction is to use ultra-high frequencies up to 100 to 200 MHz to substantially improve anatomic characterization of lesions that are small, thin, or show an infiltrative pattern. Moreover, at higher frequencies the basement membrane, which is the landmark to determine the invasive nature of epidermal skin cancers, could potentially be evaluated reliably in vivo prior to biopsy. Finally, it is important for scientists and industries to work together to develop techniques and innovative instrument modifications to the current technology that can in order to compensate for the angle of the curvature of the skin.

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