Diffusion tensor imaging and fiber tractography for the visualization of the female pelvic floor

Tissue Characterization of Puborectalis Muscle From 3-D Ultrasound

Pelvic floor (PF) muscles have the role of preventing pelvic organ descent. The puborectalis muscle (PRM), which is one of the female PF muscles, can be damaged during child delivery. This damage can potentially cause irreversible muscle trauma and even lead to an avulsion, which is disconnection of the muscle from its insertion point, the pubic bone. Ultrasound imaging allows diagnosis of such trauma based on comparison of geometric features of a damaged muscle with the geometric features of a healthy muscle. Although avulsion, which is considered severe damage, can be diagnosed, microdamage within the muscle itself leading to structural changes cannot be diagnosed by visual inspection through imaging only. Therefore, we developed a quantitative ultrasound tissue characterization method to obtain information on the state of the tissue of the PRM and the presence of microdamage in avulsed PRMs. The muscle was segmented as the region of interest (ROI) and further subdivided into six regions of interest (sub-ROIs). Mean echogenicity, entropy and shape parameter of the statistical distribution of gray values were analyzed on two of these sub-ROIs nearest to the bone. The regions nearest to the bones are also the most likely regions to exhibit damage in case of disconnection or avulsion. This analysis was performed for both the muscle at rest and the muscle in contraction. We found that, for PRMs with unilateral avulsion compared with undamaged PRMs, the mean echogenicity (p = 0.02) and shape parameter (p < 0.01) were higher, whereas the entropy was lower (p < 0.01). This method might be applicable to quantification of PRM damage within the muscle.

Anorectal Anatomy and Function

Anatomy of pelvic floor muscles has long been controversial. Novel imaging modalities, such as three-dimensional transperineal ultrasound imaging, MRI, and diffusion tensor imaging, have revealed unique myoarchitecture of the external anal sphincter and puborectalis muscle. High-resolution anal manometry, high-definition anal manometry, and functional luminal imaging probe are important new tools to assess anal sphincter and puborectalis muscle function. Increased understanding of the structure and function of anal sphincter complex/pelvic floor muscle has improved the ability to diagnose patients with pelvic floor disorders. New therapeutic modalities to treat anal/fecal incontinence and other pelvic floor disorders will emerge in the near future.

In vivo evaluation of the levator ani muscle in primiparous women using diffusion tensor imaging and fiber tractography

OBJECTIVE

To characterize the levator ani muscle (LAM) injury after first vaginal delivery and investigate the clinical application of diffusion tensor imaging (DTI) and fiber tractography in evaluating the LAM.

METHODS

Fifty-eight primiparous women at 6 weeks after vaginal delivery and 27 nulliparous women as controls underwent T2-weighted sequence and DTI sequence of the pelvic floor. A LAM scoring system was used to characterize the morphological changes. Fiber tractography of each major subdivision of LAM was performed, followed by assessment of the quality of fiber tracking. Fractional anisotropy (FA), apparent diffusion coefficient (ADC), fiber volume, and length were calculated.

RESULTS

Puborectalis and iliococcygeus injuries were observed in 30/58 (51.7%) and 10/58 (17.2%) primiparae, respectively. No LAM defects were identified in the control group. For the puborectalis, the FA values were lower (P = 0.010) and ADC values were higher (P = 0.024) in the primiparous group than in the control group. For the iliococcygeus, the fiber volume values were lower in the primiparous group than in the control group (P = 0.004).

CONCLUSION

Vaginal delivery can result in LAM injury at the puborectalis. DTI parameters can assist in the quantitative diagnosis of the LAM injury.

Evaluation of the female bladder neck and urethra using MRI with fiber tractography: Prospective study on a large cohort of continent women

AIMS

To prospectively evaluate the performance of a last generation magnetic resonance imaging (MRI) device with tractography to identify the normal female urethral sphincters in terms of morphology and quantification on a large cohort of continent women.

METHODS

We have recorded the data of 75 continent women who underwent a diffusion tensor imaging (DTI) sequence with fiber tractography during a pelvic MR examination. Three groups of age were analyzed in terms of color fiber tracking quality and quantitative parameters (fractional anisotropy [FA] and mean diffusibility [MD]). Statistical analysis was done for the qualitative assessment using weighted kappa statistics of Cohen and for the quantitative parameters using a non-parametric Kruskal-Wallis test.

RESULTS

For all cases, fiber-tracking resulted in a satisfactory representation of the complexity of the orientation of the fibers. The interobserver concordance of qualitative data was substantial, calculated at 0.78 (confidence interval: 0.71-0.85). For FA, there was no statistically significant difference with the age between the three urethral segments (p > 0.05). However, we registered a significant difference inside each group between the different segments (p < 0.05), corresponding to different orientation of fibers. For MD, we have found a statistically significant difference both between levels inside each group and according the age, meaning a variation of the water mobility for each type of musculature and with age (p < 0.05).

CONCLUSION

DTI with fiber tractography performed on a recent MR unit is a robust method for the three-dimensional visualization of the details and connections of the urethral female sphincters. Quantitative variations with age need to be considered.

Treatment of Stress Urinary Incontinence with Muscle Stem Cells and Stem Cell Components: Chances, Challenges and Future Prospects

Urinary incontinence (UI) is a major problem in health care and more than 400 million people worldwide suffer from involuntary loss of urine. With an increase in the aging population, UI is likely to become even more prominent over the next decades and the economic burden is substantial. Among the different subtypes of UI, stress urinary incontinence (SUI) is the most prevalent and focus of this review. The main underlying causes for SUI are pregnancy and childbirth, accidents with direct trauma to the pelvis or medical treatments that affect the pelvic floor, such as surgery or irradiation. Conservative approaches for the treatment of SUI are pelvic physiotherapy, behavioral and lifestyle changes, and the use of pessaries. Current surgical treatment options include slings, colposuspensions, bulking agents and artificial urinary sphincters. These treatments have limitations with effectiveness and bear the risk of long-term side effects. Furthermore, surgical options do not treat the underlying pathophysiological causes of SUI. Thus, there is an urgent need for alternative treatments, which are effective, minimally invasive and have only a limited risk for adverse effects. Regenerative medicine is an emerging field, focusing on the repair, replacement or regeneration of human tissues and organs using precursor cells and their components. This article critically reviews recent advances in the therapeutic strategies for the management of SUI and outlines future possibilities and challenges.

Novel Application of Photogrammetry to Quantify Fascicle Orientations of Female Cadaveric Pelvic Floor Muscles

Although critical for understanding and simulating pelvic floor muscle function and pathophysiology, the fascicle arrangements of the coccygeus and levator ani remain mostly undetermined. We performed close-range photogrammetry on cadaveric pelvic floor muscles to robustly quantify surface fascicle orientations. The pelvic floor muscles of 5 female cadavers were exposed through anatomic dissections, removed en bloc, and photographed from every required angle. Overlapping images were mapped onto in silico geometries and muscle fascicles were traced manually. Tangent vectors were calculated along each trace; interpolated to define continuous, 3D vector fields; and projected onto axial and sagittal planes to calculate angles with respect to the pubococcygeal line. Contralateral and ipsilateral pelvic floor muscles were compared within each donor (Kuiper's tests) and using mean values from all donors (William-Watsons tests). Contralateral muscles and all but one ipsilateral muscle pair differed significantly within each donor (p < 0.001). When mean values were considered collectively, no contralateral or ipsilateral statistical differences were found but all muscles compared differed by more than 10° on average. Close-range photogrammetry and subsequent analyses robustly quantified surface fascicle orientations of the pelvic floor muscles. The continuous, 3D vector fields provide data necessary for improving simulations of the female pelvic floor muscles.

Evaluation of Urinary Sphincter Function by Rapid Magnetic Resonance Diffusion Tensor Imaging

Purpose

This study aimed to assess the feasibility of a rapid diffusion tensor imaging (DTI) for evaluation of the female urinary sphincter function based on differentiation between rest and muscle contraction.

Methods

Magnetic resonance imaging (MRI) of the lower pelvis was performed at 3 Tesla in 10 healthy female volunteers (21–36 years; body mass index, 20.8±3.6 kg/m²) between June and July 2019. High-resolution T1- and T2-weighted images were acquired for anatomical reference, and following DTI performed in 4 experiment phases: twice during rest (denoted rest-1, rest-2) and contraction (contraction-1, contraction-2). Manual segmentation of the urinary sphincter and the levator ani muscles were performed by 2 independent readers. Mean diffusivity (MD) and fractional anisotropy (FA) values derived from DTI volumes were compared in search for significant differences between the experiment phases. Interreader agreement was assessed by intraclass correlation coefficient (ICC).

Results

Kruskal-Wallis test showed significant differences between MD values among all the experiment phases, by both independent readers (1st: X² [3,76]=17.16, P<0.001 and 2nd: X² [3,76]=15.88, P<0.01). Post hoc analysis revealed differences in MD values by both readers between: rest-1 vs. contraction-1 (least P<0.05), rest-1 vs. contraction-2 (P<0.01), rest-2 vs. contraction-1 (P<0.03), rest-2 vs. contraction-2 (P=0.02) with overall mean ‘rest’ to ‘contraction’ ΔMD=20.6%. No MD or FA differences were found between rest-1 vs. rest-2 and contraction-1 vs. contraction-2 among all the experiment phases, and interreader agreement was ICC=0.85 (MD) and ICC=0.79 (FA).

Conclusions

Rapid DTI might prospectively act as a supporting tool for the evaluation of female pelvic floor muscle function, and incontinence assessment.

In Vivo Imaging-Based 3-Dimensional Pelvic Prototype Models to Improve Education Regarding Sexual Anatomy and Physiology

BACKGROUND

Myths, misconceptions, and taboos about sexual anatomy and physiology are common and can affect sexual health and maintain harmful practices and beliefs.

AIM

To construct a female and a preliminary male 3-dimensional (3D) pelvic model on the basis of in vivo imaging, which could be studied in sex education and clinical practice.

METHODS

We retrospectively studied the images of 200 female pelvic magnetic resonance examinations and reviewed the literature to choose the optimum magnetic resonance imaging (MRI) protocol for the study of the clitoris and surrounding organs. We also conducted a cross-sectional study of 30 women who were undergoing a pelvic MRI. 15 women had undergone female genital mutilation/cutting involving the clitoris and 15 had not. The best-quality MRI images of 3 uncut and 1 cut clitoris, together with the principal surrounding pelvic organs, were selected to generate 3D reconstructions using dedicated software. The same software was used to reconstruct the anatomy of the penis and the principal surrounding pelvic organs, based on contrast-enhanced computer tomography images. Images of both models were exported in .stl format and cleaned to obtain single manifold objects in free, open source software. Each organ model was sliced and 3D printed. A preliminary feedback was collected from 13 potential users working in urology, gynaecology, sexual medicine, physiotherapy, and education.

OUTCOMES

The main outcomes of this study are a kit of 3D pelvic models, 2-dimensional figures of female and male sexual anatomy, and files for 3D printing.

RESULTS

We present a kit containing 3D models and 2-dimensional figures of female and male sexual anatomy, based on in vivo imaging and, feedbacks and suggestions received from potential users.

CLINICAL TRANSLATION

Our kit can be used in anatomy and sex education among and by health professionals, teachers, sex educators, students, and the general population.

STRENGTHS & LIMITATIONS

The strengths are that the models were based on in vivo imaging, can be dismantled/reassembled, and show analogous anatomic structures of the clitoris and the penis. The female models represent diversity, including women with female genital mutilation/cutting. The limitations are that the male model is preliminary and can be improved if based on an MRI; that imaging-based anatomic representations can differ from anatomic dissections; and that the models represent the sexual organs at rest or during an unknown state of arousal only.

CONCLUSION

Our kit can be studied in anatomy, biology, and sex education, as well as in clinical practice. Abdulcadir J, Dewaele R, Firmenich N, et al. In Vivo Imaging-Based 3-Dimensional Pelvic Prototype Models to Improve Education Regarding Sexual Anatomy and Physiology. J Sex Med 2020;17:1590-1602.

Connectivity of the Superficial Muscles of the Human Perineum: A Diffusion Tensor Imaging-Based Global Tractography Study

Despite the importance of pelvic floor muscles, significant controversy still exists about the true structural details of these muscles. We provide an objective analysis of the architecture and orientation of the superficial muscles of the perineum using a novel approach. Magnetic Resonance Diffusion Tensor Images (MR-DTI) were acquired in 10 healthy asymptomatic nulliparous women, and 4 healthy males. Global tractography was then used to generate the architecture of the muscles. Micro-CT imaging of a male cadaver was performed for validation of the fiber tracking results. Results show that muscles fibers of the external anal sphincter, from the right and left side, cross midline in the region of the perineal body to continue as transverse perinea and bulbospongiosus muscles of the opposite side. The morphology of the external anal sphincter resembles that of the number '8' or a "purse string". The crossing of muscle fascicles in the perineal body was supported by micro-CT imaging in the male subject. The superficial muscles of the perineum, and external anal sphincter are frequently damaged during child birth related injuries to the pelvic floor; we propose the use of MR-DTI based global tractography as a non-invasive imaging technique to assess damage to these muscles.

Effect of androgen deprivation and radiation therapy on MRI fiber tractography in prostate cancer: can we assess treatment response on imaging?

OBJECTIVE

To evaluate quantitative changes in Diffusion Tensor Magnetic Resonance Tractography in prostate cancer following androgen deprivation and radiation therapy.

METHODS

22 patients with elevated PSA and biopsy proven prostate carcinoma who underwent MRI of the prostate at 1.5 T with an endorectal coil were included. Group A) was the study group (n = 11), participants who underwent androgen deprivation and/or radiation therapy and group B) were Gleason-matched control group (n = 11) participants who did not undergo such therapy. Diffusion weighted images were used to generate three-dimensional (3D) map of fiber tracts from DTI. 3D regions of interest (ROI) were drawn over the tumor and healthy prostatic parenchyma in both groups to record tract number and tract density. Tumor region and normal parenchymal tract densities within each group were compared.

RESULTS

Mean tract density in the tumor region and normal parenchyma was 2.3 and 3.3 in study group (tract numbers: 116.6 and 170.2 respectively) and 1.6 and 2.7 in the control group respectively (tract numbers: 252.5 and 346.3 respectively). The difference between these values was statistically significant for the control group (p = 0.0018) but not for the study group (p = 0.11). The difference between the tract numbers of tumor and normal parenchyma appears to narrow following therapy.

CONCLUSION

The study demonstrated utility in using tractography as a biomarker in prostate cancer patients post treatment.

ADVANCES IN KNOWLEDGE

Quantitative DTI fiber tractography is a promising imaging biomarker to quantitatively assess treatment response in the setting of post-androgen deprivation and radiation therapy for prostate cancer.

Clinical and MRI changes of puborectalis and iliococcygeus after a short period of intensive pelvic floor muscles training with or without instrumentation : A prospective randomized controlled trial

PURPOSE

This study evaluates the impact of a 3-week period of intensive pelvic floor muscles training (PFMT), with or without instrumentation, on clinical and static magnetic resonance imaging (MRI) changes of puborectalis (PR) and iliococcygeus (IL) muscles.

METHODS

24 healthy young women were enrolled in the study and 17 achieved the 9 sessions of 30 min training exercises and conducted all assessments. Participants were randomly assigned in two training groups: voluntary contractions combined with hypopressive exercises (HYPO) or biofeedback exercises combined with transvaginal electrical stimulations (ELEC). Clinical and T2-weighted MRI assessments were realized before and after training.

RESULTS

Modified Oxford Grading System (MOGS) scores for left PR and perineal body significantly increased in the two groups (p = 0.039, p = 0.008), but MOGS score for right PR significantly increased only in HYPO (p = 0.020). Muscle volumes of right and left IL significantly decreased (p = 0.040, p = 0.045) after training as well as signal intensities of right and left PR (p = 0.040, p = 0.021) and thickness of right and left IL at mid-vagina location (p = 0.012, p = 0.011).

CONCLUSIONS

A short period of intensive PFMT induces clinical and morphological changes in PFMs at rest suggesting a decrease in IL volume and adipose content of PR. Although the results suggested that an intensive non-instrumented PFMT is as effective as an instrumented training, future controlled studies with greater sample sizes are needed to establish the relative and absolute effectiveness of each of the two interventions.

Modern Theories of Pelvic Floor Support : A Topical Review of Modern Studies on Structural and Functional Pelvic Floor Support from Medical Imaging, Computational Modeling, and Electromyographic Perspectives

PURPOSE OF REVIEW

Weakened pelvic floor support is believed to be the main cause of various pelvic floor disorders. Modern theories of pelvic floor support stress on the structural and functional integrity of multiple structures and their interplay to maintain normal pelvic floor functions. Connective tissues provide passive pelvic floor support while pelvic floor muscles provide active support through voluntary contraction. Advanced modern medical technologies allow us to comprehensively and thoroughly evaluate the interaction of supporting structures and assess both active and passive support functions. The pathophysiology of various pelvic floor disorders associated with pelvic floor weakness is now under scrutiny from the combination of (1) morphological, (2) dynamic (through computational modeling), and (3) neurophysiological perspectives. This topical review aims to update newly emerged studies assessing pelvic floor support function among these three categories.

RECENT FINDINGS

A literature search was performed with emphasis on (1) medical imaging studies that assess pelvic floor muscle architecture, (2) subject-specific computational modeling studies that address new topics such as modeling muscle contractions, and (3) pelvic floor neurophysiology studies that report novel devices or findings such as high-density surface electromyography techniques. We found that recent computational modeling studies are featured with more realistic soft tissue constitutive models (e.g., active muscle contraction) as well as an increasing interest in simulating surgical interventions (e.g., artificial sphincter). Diffusion tensor imaging provides a useful non-invasive tool to characterize pelvic floor muscles at the microstructural level, which can be potentially used to improve the accuracy of the simulation of muscle contraction. Studies using high-density surface electromyography anal and vaginal probes on large patient cohorts have been recently reported. Influences of vaginal delivery on the distribution of innervation zones of pelvic floor muscles are clarified, providing useful guidance for a better protection of women during delivery. We are now in a period of transition to advanced diagnostic and predictive pelvic floor medicine. Our findings highlight the application of diffusion tensor imaging, computational models with consideration of active pelvic floor muscle contraction, high-density surface electromyography, and their potential integration, as tools to push the boundary of our knowledge in pelvic floor support and better shape current clinical practice.

Quantitative study of prostate cancer using three dimensional fiber tractography

AIM: To investigate feasibility of a quantitative study of prostate cancer using three dimensional (3D) fiber tractography.

METHODS: In this institutional review board approved retrospective study, 24 men with biopsy proven prostate cancer underwent prostate magnetic resonance imaging (MRI) with an endorectal coil on a 1.5 T MRI scanner. Single shot echo-planar diffusion weighted images were acquired with b = 0.600 s/mm², six gradient directions. Open-source available software TrackVis and its Diffusion Toolkit were used to generate diffusion tensor imaging (DTI) map and 3D fiber tracts. Multiple 3D spherical regions of interest were drawn over the areas of tumor and healthy prostatic parenchyma to measure tract density, apparent diffusion coefficient (ADC) and fractional anisotropy (FA), which were statistically analyzed.

RESULTS: DTI tractography showed rich fiber tract anatomy with tract heterogeneity. Mean tumor region and normal parenchymal tract densities were 2.53 and 3.37 respectively (P < 0.001). In the tumor, mean ADC was 0.0011 × 10^-3 mm²/s vs 0.0014 × 10^-3 mm²/s in the normal parenchyma (P < 0.001). The FA values for tumor and normal parenchyma were 0.2047 and 0.2259 respectively (P = 0.3819).

CONCLUSION: DTI tractography of the prostate is feasible and depicts congregate fibers within the gland. Tract density may offer new biomarker to distinguish tumor from normal tissue.

Diffusion weighted magnetic resonance imaging and its recent trend-a survey

Since its inception in 1985, diffusion weighted magnetic resonance imaging has been evolving and is becoming instrumental in diagnosis and investigation of tissue functions in various organs including brain, cartilage, and liver. Even though brain related pathology and/or investigation remains as the main application, diffusion weighted magnetic resonance imaging (DWI) is becoming a standard in oncology and in several other applications. This review article provides a brief introduction of diffusion weighted magnetic resonance imaging, challenges involved and recent advancements.

Assessment of Postoperative Tendon Quality in Patients With Achilles Tendon Rupture Using Diffusion Tensor Imaging and Tendon Fiber Tracking

Although pre- and postoperative imaging of Achilles tendon rupture (ATR) has been well documented, radiographic evaluations of postoperative intratendinous healing and microstructure are still lacking. Diffusion tensor imaging (DTI) is an innovative technique that offers a noninvasive method for describing the microstructure characteristics and organization of tissues. DTI was used in the present study for quantitative assessment of fiber continuity postoperatively in patients with acute ATR. The data from 16 patients with ATR from 2005 to 2012 were retrospectively analyzed. The microstructure of ART was evaluated using tendon fiber tracking, tendon continuity, fractional anisotropy, and apparent diffusion coefficient values by way of DTI. The distal and proximal portions were measured separately in both the ruptured and the healthy extremities of each patient. The mean patient age was 41.56 ± 8.49 (range 26 to 56) years. The median duration of follow-up was 21 (range 6 to 80) months. The tendon fractional anisotropy values of the ruptured Achilles tendon were significantly lower statistically than those of the normal side (p = .001). However, none of the differences between the 2 groups with respect to the distal and proximal apparent diffusion coefficient were statistically significant (p = .358 and p = .899, respectively). In addition, the fractional anisotropy and apparent diffusion coefficient measurements were not significantly different in the proximal and distal regions of the ruptured tendons compared with the healthy tendons. The present study used DTI and fiber tracking to demonstrate the radiologic properties of postoperative Achilles tendons with respect to trajectory and tendinous fiber continuity. Quantifying DTI and fiber tractography offers an innovative and effective tool that might be able to detect microstructural abnormalities not appreciable using conventional radiologic techniques.