Clinical Review

Imaging Tools for Noninvasive Hair Assessment

Cutis. 2023 July;112(1):E52-E57 | doi:10.12788/cutis.0834

Trichology tools historically have been limited in their ability to provide noninvasive detailed assessments of the hair and scalp. Recent advances in diagnostic and treatment monitoring technologies have begun to fill this gap. Global photography previously relied on a film camera and stereotactic imaging equipment but has been simplified by the advent of cameras that use software analysis and provide adjustable outlines to match facial features for the capture of standardized views. Reflectance confocal microscopy (RCM) and optical coherence tomography (OCT) both enable in vivo visualization of subcutaneous structures and provide new insight into the dynamic subclinical changes of alopecia. Recent efforts focus on training convolutional neural networks to quantify various hair parameters on OCT scans. When scalp biopsy is necessary, trichoscopy, RCM, and OCT can guide in selecting biopsy sites. Because of the growing clinical applications of these technologies, clinicians should be aware of the advantages and limitations of noninvasive hair-imaging tools.

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Practice Points

Reflectance confocal microscopy (RCM) imaging can be taken at levels from the stratum corneum to the papillary dermis and can be used to study scalp discoid lupus, lichen planopilaris, frontal fibrosing alopecia, alopecia areata, and androgenetic alopecia.
Because of its ability to distinguish different stages of disease, RCM can be recommended as an intermediate step between trichoscopy and histology for the diagnosis and management of hair disease.
Optical coherence tomography has the potential to monitor early subclinical responses to alopecia therapies while also improving hair transplantation outcomes by allowing for visualization of the subcutaneous angle of hair follicles.
Software development paired with trichoscopy has the ability to quantify hair growth parameters such as hair count, density, and diameter.

References

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New imaging tools along with adaptations to existing technologies have been emerging in recent years, with the potential to improve hair diagnostics and treatment monitoring. We provide an overview of 4 noninvasive hair imaging technologies: global photography, trichoscopy, reflectance confocal microscopy (RCM), and optical coherence tomography (OCT). For each instrument, we discuss current and future applications in clinical practice and research along with advantages and disadvantages.

Global Photography

Global photography allows for the analysis of hair growth, volume, distribution, and density through serial standardized photographs.¹ Global photography was first introduced for hair growth studies in 1987 and soon after was used for hair and scalp assessments in finasteride clinical trials.²

Hair Assessment—Washed, dried, and combed hair, without hair product, are required for accurate imaging; wet conditions increase reflection and promote hair clumping, thus revealing more scalp and depicting the patient as having less hair.¹ Headshots are taken from short distances and use stereotactic positioning devices to create 4 global views: vertex, midline, frontal, and temporal.³ Stereotactic positioning involves fixing the patient’s chin and forehead as well as mounting the camera and flash device to ensure proper magnification. These adjustments ensure lighting remains consistent throughout consecutive study visits.⁴ Various grading scales are available for use in hair growth clinical studies to increase objectivity in the analysis of serial global photographs. A blinded evaluator should assess the before and after photographs to limit experimenter bias. Global photography often is combined with quantitative software analysis for improved detection of hair changes.¹

Advancements—Growing interest in improving global photography has resulted in various application-based, artificial intelligence (AI)–mediated tools to simplify photograph collection and analysis. For instance, new hair analysis software utilizes AI algorithms to account for facial features in determining the optimal angle for capturing global photographs (Figure 1), which simplifies the generation of global photography images through smartphone applications and obviates the need for additional stereotactic positioning equipment.^5,6

FIGURE 1. Global photography provides adjustable outlines for consistent head positioning.

Limitations—Clinicians should be aware of global photography’s requirements for consistency in lighting, camera settings, film, and image processing, which can limit the accuracy of hair assessment over time if not replicated correctly.^7,8 Emerging global photography software has helped to overcome some of these limitations.

Global photography is less precise when a patient’s hair loss is less than 50%, as it is difficult to discern subtle hair changes. Thus, global photography provides limited utility in assessing minimal to moderate hair loss.⁹ Currently, global photography largely functions as an adjunct tool for other hair analysis methods rather than as a stand-alone tool.

Trichoscopy

Trichoscopy (also known as dermoscopy of the hair and scalp) may be performed with a manual dermoscope (with 10× magnification) or a digital videodermatoscope (up to 1000× magnification).^10-12 Unlike global photography, trichoscopy provides a detailed structural analysis of hair shafts, follicular openings, and perifollicular and interfollicular areas.¹³ Kinoshita-Ise and Sachdeva¹³ provided an in-depth, updated review of trichoscopy terminology with their definitions and associated conditions (with prevalence), which should be referenced when performing trichoscopic examination.

Affixing a Scalp Dressing With Hairpins

Imaging Tools for Noninvasive Hair Assessment

References

Global Photography

Trichoscopy

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