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Arch Aesthetic Plast Surg > Volume 29(2); 2023 > Article
Park, Ho, and Manonukul: Hair diameter measurement methods: micrometer caliper versus phototrichogram

Abstract

Background

Hair diameter is a crucial element in deciding the treatment and predicting the prognosis of hair transplantation in patients with hair loss.

Methods

Ten female volunteers participated in this study. Three sites at different horizontal positions of the scalp were chosen for measurement: midoccipital, mastoid, and temporal. Three boxes of 1 cm2 were marked from superior to inferior along the midline of each site, and five anagen hairs ≥10 cm long were randomly sampled from each box. The thickness of each collected hair was measured at three positions along the hair length: 1 cm, 5 cm, and 10 cm from the surface of the skin. The diameters of the hairs were measured using a micrometer caliper and a Folliscope phototrichogram, and the measurements were compared.

Results

The average thickness of all hairs was 76.90±12.29 μm when measured with the caliper and 108.78±19.97 μm when measured with the phototrichogram. There was a statistically significant difference between the two measurement methods (P<0.001). The average hair thickness from the three areas (midoccipital, mastoid, and temporal) showed a significant difference between the caliper and the Folliscope hair measurements (P<0.001): midoccipital area (caliper, 74.46±9.71 μm; Folliscope, 109.03±19.59 μm), mastoid area (caliper, 76.36±10.67 μm; Folliscope, 103.73±18.67 μm), and temporal area (caliper, 79.89±15.18 μm; Folliscope, 113.59±20.43 μm).

Conclusions

Measuring hair thickness using a phototrichogram, which generates a measurement of the long-axis dimension, is clinically useful in the treatment of patients with hair loss and patients undergoing hair transplantation.

INTRODUCTION

Hair diameter is a crucial element in deciding the treatment and predicting the prognosis of hair transplantation in patients with hair loss [1-3]. Ishino et al. [4] reported that a decrease in hair thickness, rather than a decrease in hair density, was the main finding in men with androgenetic alopecia.
Hair diameter is the most crucial prognostic factor in determining the surgical results of hair transplantation. Higher volume and coverage can be achieved with transplantation of thick donor hairs. Meanwhile, thin-caliber hairs are needed to mimic the natural texture of eyebrows, eyelashes, the female hairline, sideburns, and the temporal region [5-7]. Thus, the measurement of hair caliber has clinical importance in planning hair transplant surgery, evaluating the progression of hair loss, and determining the effectiveness of hair loss treatment.
Hair caliber is typically measured using a micrometer caliper or a phototrichogram [8,9]. In addition, Erdogan et al. [10] introduced the KEBOT system, an artificial intelligence-based comprehensive analysis system for hair transplant surgery with follicular unit excision and noted that the measurements of hair diameter converged along the length of the long axis of the hair shaft.
Bayramoglu et al. [9] compared the diameter of hair measured using a scanning electron microscope and a micrometer caliper and demonstrated that the caliper measured the length of the short axis of the hair.
The two primary methods of measuring hair caliber include the micrometer caliper, which physically and mechanically measures hair thickness, and the phototrichogram, which measures hair thickness by an imaging process. This study compared the two methods of measuring hair on various parts of the scalp.

METHODS

Ten female volunteers participated in the study. All procedures performed were in accordance with the Declaration of Helsinki (as revised in 2013). Institutional review board approval was not required as this report was not a prospective or systematic investigation of treatment. All participants were Korean and had black hair. The participants’ age ranged from 25 to 41 years with a mean of 33 years. Candidates with a history of previous hair transplantation surgery, hair disease, or face-lift surgery were excluded.
Three sites at different horizontal positions (hereafter referred to as horizontal sites) were chosen for measurement: midoccipital, mastoid, and temporal (Fig. 1). At each site, three 1 cm2 boxes were marked from superior to inferior along the midline of the site, and hair samples were randomly collected from these boxes (hereafter referred to as vertical boxes). The midoccipital point at the upper border of the helical rim was set as a reference point. The point directly above the reference point was designated as the middle point (M), the point below as the inferior point (I), and the point above the middle point as the superior point (S).
Five anagen hairs ≥10 cm long were randomly sampled from each box. The hairs were screened by a highly experienced hair surgeon to ensure they were in the anagen phase. The thickness of the collected hairs was measured at three positions: 1 cm, 5 cm, and 10 cm from the surface of the skin. There were 1,350 measurements overall: 45 hairs per person were collected (a total of 450 hairs) and measurements were made at three positions for each hair.
The diameters of the hairs were measured using an electronic micrometer caliper (Baoshishan) and a Folliscope phototrichogram (LeadM), and the resulting data were compared and statistically analyzed (Figs. 2, 3).

Statistical analysis

SPSS version 25.0 (IBM Corp., Armonk, NY, USA) was used for statistical analysis. A paired-sample t-test was performed to find the difference in the measurement of hair thickness between the caliper and the Folliscope. A four-way analysis of variance was performed to compare the measurements of the four major analysis variables (the 10 participants, the horizontal site, the vertical box, and the position along the hair length). Multivariate analysis of variance (MANOVA) was performed to investigate differences in the measurements between the caliper and the Folliscope in terms of the horizontal site, vertical box, and position along the hair length.

RESULTS

The thickness of all hairs was 76.90±12.29 μm when measured with the caliper and 108.78±19.97 μm when measured with the Folliscope. There was a statistically significant difference between the two measurement methods (P<0.001).

Difference in measurements between the caliper and Folliscope

Paired-sample t-tests were performed to examine differences in measurements between the caliper and Folliscope.

All measurements

A statistically significant difference was found between the hair measurements of the caliper and the Folliscope (t=−60.301, P<0.001; paired-sample t-test). The average diameter was 76.90±12.29 μm with the caliper and 108.78±19.97 μm with the Folliscope.

Midoccipital

A statistically significant difference was found between the midoccipital hair measurements of the caliper and the Folliscope (t=−41.456, P<0.001; paired-sample t-test). The average diameter was 74.46±9.71 μm with the caliper and 109.03±19.59 μm with the Folliscope.

Mastoid

A statistically significant difference was found between the mastoid hair measurements of the caliper and the Folliscope (t=−32.1186, P<0.001; paired-sample t-test). The average hair diameter was 76.36±10.67 μm with the caliper and 103.73±18.67 μm with the Folliscope.

Temporal

A statistically significant difference was found between the temporal hair measurements of the caliper and the Folliscope (t=−33.222, P<0.001). The average diameter was 79.89±15.18 μm with the caliper and 113.59±20.43 μm with the Folliscope.

Multivariate analysis of variance

MANOVA was performed to examine measurement differences between the caliper and Folliscope for the four major variables. The four major variables were study participants, the horizontal site (O: midoccipital, M: mastoid, T: temporal), the vertical box (S: superior, M: middle, I: inferior), and position along the hair shaft (1: at 1 cm, 5: at 5 cm, 10: at 10 cm). Significant differences were found in the measurement of hair thickness between the caliper and the Folliscope for the horizontal site (Wilks lambda=0.932, F=23.544, P=0.000), vertical box (Wilks lambda=0.983, F=5.639, P=0.000), position along the hair length (Wilks lambda=0.986, F=4.530, P=0.001) and horizontal site×vertical box (Wilks lambda=0.983, F=2.901, P=0.003).

DISCUSSION

The measurement of hair thickness is important in determining the progress of hair loss and the effect of treatment. Such measurement is also important in hair transplant surgery. Hair caliber is an important element in surgical planning, predicting the prognosis, and assessing results.
A review of existing studies revealed two primary methods for measuring the thickness of hair: a mechanical and physical method using a micrometer caliper and a digital imaging method using a phototrichogram.
Various theories have been proposed for the cause of curly hair. One representative theory is that the structural differences of cell types and their lateral segregation are the main factors driving curl formation. In general, straight hair has a rounded cross-section, whereas curly hair has a flatter, elliptical cross-section [11,12].
Thicker hair tends to be frizzier and has a greater difference between the lengths of the long axis and short axis. Bryant and Porter observed a highly significant relationship between curliness and ellipticity in African hair [13].
Erdogan et al. [10] introduced the KEBOT system, a new robotic and vision-based imaging system and artificial intelligence-based analysis approach and stated that the thickness measured by digital image processing converges along the long-axis dimension of the hair. Bayramoglu et al. [9] reported that a measurement by micrometer caliper represents the short-axis dimension of the hair. The KEBOT system has many advantages in terms of measuring density and coverage value (CV), and the entire scalp can be easily scanned by region. However, because the head must be shaved before taking measurements, the system can be used only prior to surgery and cannot be used in follow-up visits when hair has grown out or in surgical cases that do not require shaving of the donor area, such as in long-hair or non-shaven follicular unit excision. The system is also difficult to purchase.
The micrometer caliper has disadvantages in that hair strands must be cut one by one, and its measurements are largely representative of the short-axis dimension.
Measurements made using a phototrichogram are easy to calculate and do not require shaving. They are close to the long-axis dimension and more comparable to the thickness of hair as visualized by the human eye.
The present study, like that of Bayramoglu et al. [9], found that the measurements obtained with the micrometer caliper compared to those obtained with the Folliscope were significantly different, presumably due to the elliptical shape of the hair shaft cross-section.
Harris introduced the concept of the hair diameter index (HDI) [14], expressed as
HDI=HSD×(hairs/cm2)/100,
where HSD is the hair shaft diameter, measured in μm.
The HDI ranges between 1 and 200 when the HSD is measured in μm. Erdogan introduced the CV, a concept similar to the HDI [9]. The CV is calculated as follicular units per square centimeter multiplied by the number of hairs per follicle and average hair diameter. Both the HDI and CV provide a mathematical criterion for adequate coverage in hair transplantation. The CV and HDI, as measures of scalp coverage, represent coverage of the scalp as seen by the human eye. Therefore, the coverage of the scalp is more strongly related to the long-axis dimension than the short-axis dimension of the elliptical hair shaft.
In this study, both the caliper and Folliscope showed a statistically significant difference in each measurement site and in the overall sum (P<0.001) (Table 1). When directly comparing the average values, there was a difference of approximately 30%. Although there have been reports that investigated caliper and Folliscope measurements separately or showed their association with the short axis and the long axis, this study is the first to make a direct comparison of the two methods in the same patients and confirm a major difference.
Since the degree of scalp coverage is associated with the visual effect of hair transplantation, the long axis value is clinically more significant than the short axis.
Mechanically measuring the thickness of each hair strand with a micro-caliper can be difficult and time-consuming, even more so when working with many hairs. Also, the short axis of the hair that it measures, does not accurately reflect the perceived scalp coverage.
The Folliscope phototrichogram takes a high-resolution photo of the hair shaft to visually measure its caliber. As this reflects the long axis of the hair, its measurements have a stronger correlation with scalp coverage. Moreover, the Folliscope allows for easier measurements and can be stored for follow-up visits.
Based on its advantages, the measurement of hair thickness using a phototrichogram, which is a measure of the long-axis dimension, is useful in the treatment of patients with hair loss and patients undergoing hair transplants.
In conclusion, the phototrichogram is clinically useful in the treatment of patients with hair loss and hair transplants.

CONFLICTS OF INTEREST

No potential conflict of interest relevant to this article was reported.

Notes

Ethical approval

The study was performed in accordance with the principles of the Declaration of Helsinki.

Patient consent

The participants provided written informed consent for the publication and use of their images.

Fig. 1.
Sites for hair sampling. (A) Occipital area. (B) Temporal area.
aaps-2022-00423f1.jpg
Fig. 2.
Use of the phototrichogram. (A) Photographing the scalp with phototrichogram. (B) Software for analyzing phototrichogram images.
aaps-2022-00423f2.jpg
Fig. 3.
Micrometer caliper.
aaps-2022-00423f3.jpg
Table 1.
Difference in measurements between the caliper and Folliscope
Caliper (μm) Folliscope (μm) P-value
Midoccipital 74.46 ± 9.71 109.03 ± 19.59 < 0.001
Mastoid 76.36 ± 10.67 103.73 ± 18.67 < 0.001
Temporal 79.89 ± 15.18 113.59 ± 20.43 < 0.001
Total 76.90 ± 12.29 108.78 ± 19.97 < 0.001

Values are presented as mean±SD.

REFERENCES

1. Devroye J. An overview of the donor area: basic principles. In: Unger WP, Shapiro R, Unger R, et al., editors. Hair transplantation. 5th ed. Informa Healthcare; 2011. p. 247-62.

2. Park JH, Park JM, Kim NR, et al. Hair diameter evaluation in different regions of the safe donor area in Asian populations. Int J Dermatol 2017;56:784-7.
crossref pmid pdf
3. Okochi M, Fukushima T, Okochi H, et al. Donor site of follicular unit excision hair transplantation: the relationship between appearance and actual hair density, and hair diameter. J Plast Surg Hand Surg 2020;54:172-6.
crossref pmid
4. Ishino A, Takahashi T, Suzuki J, et al. Contribution of hair density and hair diameter to the appearance and progression of androgenetic alopecia in Japanese men. Br J Dermatol 2014;171:1052-9.
crossref pmid pdf
5. Yun SS, Park JH, Na YC. Hair diameter variation in different vertical regions of the occipital safe donor area. Arch Plast Surg 2017;44:332-6.
crossref pmid pmc pdf
6. Park JH, Kim NR, Manonukul K. Eyebrow transplantation using long hair follicular unit excision technique. Plast Reconstr Surg Glob Open 2021;9:e3598.
crossref pmid pmc
7. Umar S. Use of nape and peri-auricular hair by follicular unit extraction to create soft hairlines and temples: my experience with 128 patients. Aesthet Surg J 2015;35:903-9.
crossref pmid
8. Kim JE, Lee JH, Choi KH, et al. Phototrichogram analysis of normal scalp hair characteristics with aging. Eur J Dermatol 2013;23:849-56.
crossref pmid
9. Bayramoglu A, Erdogan K, Urhan O, et al. Hair diameter measurements for planning follicular unit extraction surgery (FUE): is there a correlation between the micrometer caliper and scanning electron microscopy (SEM) findings? J Cosmet Dermatol 2022;21:1086-92.
crossref pmid pdf
10. Erdogan K, Acun O, Kucukmanisa A, et al. KEBOT: an artificial intelligence based comprehensive analysis system for FUE based hair transplantation. IEEE Access 2020;8:200461-76.
crossref
11. Wortmann FJ, Wortmann G, Sripho T. Why is hair curly? Deductions from the structure and the biomechanics of the mature hair shaft. Exp Dermatol 2020;29:366-72.
crossref pmid pdf
12. Robbins CR. Chemical and physical behavior of human hair. 2n5thd ed. Springer Verlag; 2012.

13. Bryant H, Porter CE. Hair ethnicity. In: Evans T, Wickett RR, Budzynski BW, et al., editors. Practical modern hair science. Allured Business Media; 2012. p. 193-221.

14. Harris JA. The development and application of the hair diameter index (HDI). Hair Transplant Forum Int 2021;31:1-8.
crossref
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