Ovarian tissue cryopreservation has become the standard procedure for fertility preservation in young cancer patients who are facing loss of fertility due to impending chemotherapy and radiation therapy. According to the guidelines of the American Society of Clinical Oncology (ASCO) [
1], although ovarian tissue cryopreservation is still an experimental and viable option for fertility preservation, more than 130 live births have already been reported [
2‐
4]. Furthermore, in Germany, around 400 ovarian tissue cryopreservation procedures are carried out each year [
5]. To date, more than 1500 ovarian tissue cryopreservation procedures have been performed in the Nordic countries [
6]. In addition, two live births were reported applying the new clinical procedure of ovarian tissue transplantation (IVA: in vitro activation) as a fertility treatment for patients with primary ovarian insufficiency (POI) [
7,
8]. Globally, the live birth rate from transplanted frozen-thawed ovarian tissue is approximately 30% [
3,
5,
9,
10]. Although ovarian function is well recovered among most transplanted cases [
3,
11], only 67–75% of patients had at least 1 year of ovarian tissue activity [
10]. The duration of ovarian tissue activity normally depends on the number of remaining primordial follicles contained in the transplanted ovarian tissue. The main reasons for follicle loss are “burst” or “activation” of primordial follicle recruitment and ischemic apoptosis [
3]. However, selection of ovarian tissue that includes a maximum number of primordial follicles is important for improving the outcome of ovarian tissue transplantation. Therefore, a procedure needs to be established for the assessment of ovarian reserve in ovarian tissue.
Optical coherence tomography (OCT) is a non-invasive imaging technique that provides high-resolution images for a range of clinical applications [
12,
13]. By measuring back-scattered light from microstructural features in tissues, OCT images include micron-scale detail to a penetration depth of 1–3 mm [
12,
14]. OCT has recently been used for the imaging of tissues for clinical examination of areas that can be accessed directly or by using an endoscope or catheter. OCT is used in such fields as ophthalmology [
15,
16] and dentistry [
17,
18], and to evaluate such areas of the body as the gastrointestinal tract [
19,
20], coronary blood vessels [
21,
22], colon [
23], breast [
24,
25], and more [
12,
14]. Some researchers have been investigating the application of OCT in evaluating the anatomical features of normal ovarian tissue [
13,
14,
26‐
29]. In particular, a study has been reported on the clinical application of OCT for the detection of malignant cells and to search for primordial follicles in formalin-fixed and embedded ovarian tissue for fertility preservation [
30]. In addition, researchers have recently reported a study using mice ovaries to investigate the possibility of using OCT to assess ovarian reserve [
31].
The present study investigated the possibility of using OCT to assess the localization of primordial follicles and ovarian reserve in ovarian tissue, using non-fixed human ovarian tissue that had been cryopreserved for fertility preservation due to POI and impending treatment of hematological disease and cancer.