Ultrasound News: Sound Judgment — Using 3D Diagnostic Imaging to Assess Dermal Trauma
By Robert L. Bard, MD, DABR, FASLM
Radiology Today
Vol. 21 No. 2 P. 30

Since the advent of high-resolution 3D sonograms, digital scanning and diagnostic imaging technologies have completely revolutionized treatment protocols by offering safe, accurate readings and real-time tracking. Where skin sampling and biopsies were once the primary preop clinical evaluation solution, all major skin injuries relating to acute wounds and burns required a better way to evaluate trauma depth and wound healing without the risk of complications. Use of today’s ultrasound technology provides a more effective and noninvasive evaluation of any burn’s intensity and depth during on-site diagnosis, through high-resolution point-of-care units. In addition, wound healing and complications may also be serially observed. Nonradiopaque foreign bodies can be quickly detected to allow image-guided removal with decreased morbidity. Also, 3D volumetric mapping shows nerves and vessels as well as fragments that lie outside the initial point of entry.

Depth of Injury and Tissue Viability
The use of high-resolution sonography to accurately measure burn depth is studied with the application of copious sterile gel or a sterile gel standoff pad. It is also imaged by technologies such as near-infrared spectroscopy, thermography, nuclear radiotracer analysis, fluorescent imaging, hyperspectral imaging, laser Doppler imaging (LDI), multiphoton microscopy, reflectance confocal microscopy (RCM), and optical coherence tomography. These latter systems are currently depth limited to 1 to 2 mm.1

Burn tissue viability is quantitatively evaluated by tissue vascularity and oxygenation assessable by all the vascular and perfusion imaging modalities with the depth limitations previously described. The cicatrix generally contains abundant perilesional vascular supply, allowing for better healing following reconstructive surgical procedures.2

Optimally, the burn depth is measured using standard 15 to 22 MHz probes—and experimentally from 30 to 200 MHz—and is highly reliable to find the demarcation between normal dermis and edematous tissue. The presence of calcified or carbonized skin will appear as an echogenic region where the sonic shadowing is proportional to the extent of tissue destruction and appears similar to the iceball effect of frozen human tissue, which is used as a clinical endpoint of successful thermal cryosurgery. In addition to visualizing fluid formation in the epidermis (blistering), Doppler sonography is useful for assessing the viability of tissue, which is serially and quantitatively studied by 3D Doppler histogram analysis of the injured tissue volume. In second-degree burns, improvement is demonstrated by decreasing edematous dermal thickness on interval imaging studies and, when normalized, is compared with the healthy adjacent tissue depth.

Measurement of skin thickness is variable by anatomic site and does not relate directly to function. Tissue health and successful wound healing are highly correlated with the presence of stem cell–rich sweat ducts and hair follicles, measurable by extremely high-resolution sonography and essential for reepithelialization.3 Recent studies have explored RCM imaging of burn and other wounds to track and predict healing.

Newer optical technologies with higher resolution can show microvessels that may be useful in skin grafts and tissue flaps to verify blood perfusion and avoid potential rejection. Infectious complications in serious burns create inflammatory new vessels that are readily imaged by sonograms, as well as deeper subdermal and intramuscular abscesses, which are routinely drained under ultrasound guidance procedures. Potential future noninvasive spectral and hyperspectral devices for dermal health observation, such as tissue oxygenation and vessel flow parameters, have not yet been fully studied in burn patients. While LDI is currently used in the hospital setting, the possibility of an emergency response team carrying a portable sonogram is feasible, since noncontact options are available.4

Identifying Foreign Bodies
Occurrence of penetrating foreign bodies is common in patients visiting the emergency department; however, many occur during strenuous physical activity, and emotional stress may be discounted as minor or temporary and forgotten when the pain or erythema subsides.5 The foreign body may remain asymptomatic for long periods of time or rapidly develop a wide range of complications including pain from abscess formation, chronic discharging wound, necrotizing fasciitis, granulomas leading to bone and joint destruction including tendon infiltration with shredding and tearing, vascular events including thrombophlebitis with or without pulmonary emboli, and generalized massive soft tissue injury.6-11

Some foreign bodies are radiographically visible, if metallic, or possess radiopaque content. Nonradiopaque glass and wooden fragments are often horizontally aligned with the skin surface and frequently indistinguishable on 2D sonograms from the normal fibrous septae coursing parallel to the dermis. 3D or real-time 4D imaging shows these foreign bodies in sharp contrast to the adjacent subcutaneous or musculotendinous tissue.

The body reacts to these intrusions by initiating a protective inflammatory process that produces a circumferential sphere of echo poor tissue around acute lesions. The “halo” is echo poor, sharply highlighting the more central brightly echogenic foreign body representing edema, abscess, or granulation tissue, and Doppler demonstrates peripheral neovascularity corresponding to the degree of the inflammation.11 In cases of less-severe tissue reaction, the edema or chronic inflammatory tissue may be insufficient to spotlight the foreign body. In these instances, the object generally produces an interruption of the sound beam penetration, which produces a “sonic shadow” effect that appears as a darkened vertical zone within the whiter normal tissues. An extreme example of this finding occurs when the foreign body or chronic inflammation calcifies, as we see in calcific tendinitis or the common tropical parasitic infestations that generate subcutaneous masses, which are now reaching the United States due to globalization.

Sonography is particularly important in the extremities, since weight bearing and movement affect the distribution of the foreign body in the penetrated tissues. The wood, metal, or glass may fracture with displacement of fragments or be forced into unexpected locations not predicted by the initial portal of entry.

Imaging Variables
An intratendinous location cannot be easily imaged during surgical exploration, whereas sonography can pinpoint the site before or during surgery with intraoperative probes. Surgical image-guided foreign body removal has been performed by military field surgeons for more than 20 years with highly reduced surgical morbidity, due to point-of-care portable sonogram units that transmit results over the internet or satellite phone.

Foreign bodies that lie predominantly in the horizontal plane appear as linear bright echoes, with or without the accompanying black shadow on standard 2D imaging. Since 3D sonography is multiplanar, the greatest dimension will be more easily identified in any one of the three planes that occur simultaneously while scanning. A further refinement of 3D imaging is its 4D potential, which is real-time operator adjustment of the probe angle and position to optimize the foreign body in its most recognizable silhouette.

For example, fiberglass threads are barely distinguishable from the normal nail bed structures on 2D but appear in stark contrast to the background in 3D. Splinter imaging is particularly optimized by very high–frequency probes, which can show the fragmented strands, perilesional fluid, and black sonic shadowing that may be missed by lower-frequency probes. Significant perilesional fluid allows easier extraction of the splinter and is optimally mapped at higher frequencies, potentially permitting minimally invasive removal by forceps.

Similarly, intraepidermal superficial splinters may appear as pigmented lesions to the naked eye but are quickly triangulated in depth by the 2D and 3D technology. Subdermal lesions are likewise difficult to image in 2D; however, the frequent occurrence of perilesional fluid due to local inflammatory processes creates a black background for the foreign object to be highlighted.

As noted earlier, sonography has been used by the military of advanced countries to provide point-of-care imaging and image guidance for minimally invasive extraction techniques for more than two decades. This technology was initially developed for battlefield use by H. Theodore Harcke, MD, for the US Army Special Forces units a quarter of a century ago.12 In emergent cases with military and law enforcement trauma scars, metallic fragments comingled with clothing fabric or the commonly used Kevlar vest may be included in the area of study. These foreign bodies may be located within the scar or several centimeters distant.

— Robert L. Bard, MD, DABR, FASLM, has pioneered digital imaging technologies as alternatives to surgical biopsies for dermatologic and solid organ neoplastic disease since 1972. He is the author of Image Guided Dermatologic Treatments, Image Guided Prostate Cancer Treatment, and Dynamic Contrast-Enhanced MRI Atlas of Prostate Cancer and is a member of leading international imaging societies.

1. Monstrey S, Hoeksema H, Verbelen J, Pirayesh A, Blondeel P. Assessment of burn depth and burn wound healing potential. Burns. 2008;34(6):761-769.

2. Iftimia N, Ferguson RD, Mujat M, et al. Combined reflectance confocal microscopy/optical coherence tomography imaging for skin burn assessment. Biomed Opt Express. 2013;4(5):680-695.

3. Foster FS, Zhang MY, Zhou YQ, et al. A new ultrasound instrument for in vivo microimaging of mice. Ultrasound Med Biol. 2002;28(9):1165-1172.

4. Iraniha S, Cinat Me, VanderKam VM, et al. Determination of burn depth with noncontact ultrasonography. J Burn Rehabil. 2000;21(4):333-338.

5. Tantray MD, Rather A, Manaan Q, Andleeb I, Mohammad M, Gull Y. Role of ultrasound in detection of radiolucent foreign bodies in extremities. Strategies Trauma Limb Reconstr. 2018;13(2):81-85.

6. Fakoor M. Prolonged retention of an intramedullary wooden foreign body. Pak J Med Sci. 2006;22:78-79.

7. Freund EI, Weigl K. Foreign body granuloma. A cause of trigger thumb. J Hand Surg Br. 1984;9(2):210.

8. Choudhari KA, Muthu T, Tan MH. Progressive ulnar neuropathy caused by delayed migration of a foreign body. Br J Neurosurg. 2001;15(3):263-265.

9. Meurer WJ. Radial artery pseudoaneurysm caused by occult retained glass from hand laceration. Pediatr Emerg Care. 2009;25(4):255-257.

10. Flom LL, Ellis GL. Radiologic evaluation of foreign bodies. Emerg Med Clin North Am. 1992;10(1):163-176.

11. Little CM, Parker MG, Callowich MC, Sartori JC. The ultrasonic detection of soft tissue foreign bodies. Invest Radiol. 1986;21(3):275-277.

12. Harcke HT, Rooks VJ. Sonographic localization and management of metallic fragments: a report of five cases. Mil Med. 2012;177(8):988-992.