Cancer in the female reproductive system most frequently occurs in the uterus or cervix, with endometrial cancer and cervical cancer ranked the sixth [1] and fourth [2] most common cancers globally among women [3]. Characterization of the healthy uterus and cervix, and subsequent identification of diseased tissue, is challenging as water and the cellular density of normal tissue vary during the menstrual cycle (MC). Current research using functional magnetic resonance imaging (fMRI) [[4], [5], [6]], including our own studies [7], indicate that uterine zones show dynamic changes across the MC on diffusion tensor imaging (DTI) and intravoxel incoherent motion diffusion weighted imaging (IVIM-DWI) sequences.

In the cervix, conventional MRI shows no morphological changes during the MC [8], however, fluctuating hormone levels could cause biological changes [9], which may be detected on fMRI. Additionally, the size, structure and tissue content of the cervix may change with age and parity. With respect to age, the volume of the uterus and cervix and the thickness of the endometrium and junctional zone peak in women aged 41–50 years [8], while the premature birth rate [10] and risk of maternal complications such as thrombosis [11] increase, and adverse birth outcomes are minimized [12], in women aged 29–30 years. With respect to parity, cervical remodeling may occur before and during delivery [13] and should be considered when evaluating MR images [14]. To the authors' knowledge, there are no publications exploring changes in the cervix during the MC in women of reproductive age using fMRI sequences such as IVIM-DWI.

The apparent-diffusion-coefficient (ADC) value is a quantitative parameter derived from DWI [15]. The ADC value has been validated as an imaging biomarker for diffuse or focal cervicogenic disease [[16], [17], [18], [19]] and monitoring treatment response in malignant tumors [20,21]. The ADC value is measured based on the random motion of water molecules, but the reliability of ADC values may be limited by the perfusion effect [15,22]. In contrast, the IVIM technique, which measures DWI over multiple b values [15], estimates molecular diffusion and perfusion effects separately, using the parameters D (diffusion coefficient), f (perfusion fraction), and D* (perfusion-related diffusion coefficient) [23]. D and f were significantly lower in patients with early cervical cancer and residual tumor after biopsy compared with no residual tumor [18,24,25], and all parameters except the D value may facilitate the diagnosis of cervical cancer [26]. Although the IVIM technique has been used for cervicogenic diseases [18,24,25,27], the utility of this approach may be challenged if IVIM-DWI parameters vary during the MC [7] or are influenced by age and parity. The objective of this study was to define the IVIM-DWI parameters of the healthy cervix in women of reproductive age, and the biological characteristics of this tissue across the MC. Subgroup analyses of subjects stratified by age and parity (younger [18 - < 30 years] vs. older [≥30–45 years]; parity 0 vs. parity 1 and 2) were performed.