Real-time magnetic resonance imaging (MRI): anatomical changes during physiological voiding in men

Validation of Dynamic 3D MRI for Urodynamics Assessment Using an Anatomically Realistic In Vitro Model of the Bladder

Lowery urinary tract symptoms (LUTS) affect a large majority of the aging population. 3D Dynamic MRI shows promise as a noninvasive diagnostic tool that can assess bladder anatomy and function (urodynamics) while overcoming challenges associated with current urodynamic assessment methods. However, validation of this technique remains an unmet need. In this study, an anatomically realistic, bladder-mimicking in vitro flow model was created and used to systematically benchmark 3D dynamic MRI performance using a highly controllable syringe pump. Time-resolved volumes of the synthetic bladder model were obtained during simulated filling and voiding events and used to calculate volumetric flowrate. During MRI acquisitions, pressure during each event was recorded and used to create PV loops for work assessment. Error between control and MRI-derived volume for voiding and filling events exhibited 3.36% and 4.66% differences, respectively. A slight increase in average error was observed for MRI-derived flowrate when compared to the control flowrate (4.90% and 7.67% for voiding and filling, respectively). Overall, average error in segmented volumes increased with decreasing volume flowrate. Pressure drops were observed during voiding. Pressure increased during filling. Enhanced validation of novel 3D MRI urodynamics is achieved by using high-resolution PIV for visualizing and quantifying velocity inside the bladder model, which is not currently possible with 3D Dynamic MRI.

Technical feasibility of uro-dynamic MRI study of voiding biomechanics: a pilot study

INTRODUCTION

Dynamic volumetric MRI was used to non-invasively assess voiding biomechanics in a healthy male volunteer.

METHODS

Using 3D Differential Subsampling with Cartesian Ordering (DISCO) Flex acquisition sequence, volumetric bladder images were obtained throughout the voiding effort. These were subsequently segmented using MIMICS. Segmented anatomical volumes were used to quantify total voided volume, post-void residual, volumetric displacement of urine over time, bladder neck angle, sphericity index, and prostatic urethral angle through the voiding effort.

RESULTS

Bladder sphericity index correlated positively with flow rate. The greatest degree of bladder neck funneling correlated with the maximum urine flow rate. There was straightening of the prostatic urethral angle during voiding that also correlated positively with urine flow.

CONCLUSION

This pilot study confirms the potential of dynamic MRI to provide non-invasive assessment of lower urinary tract anatomy and biomechanics during voiding.

Dynamic simulation and analysis of the influence of urethral morphological changes on urodynamics after benign prostatic hyperplasia surgery: A computational fluid dynamics study

BACKGROUND AND OBJECTIVE

Computational fluid dynamics (CFD) technology has been widely used in medicine to simulate and analyse urine flow characteristics in urology. In previous studies, researchers have modelled the analysis with a simple circular urethra, ignoring the effect of the patient's true urethral morphology on the urinary flow rate. Moreover, the studies tended to be steady-state simulations rather than dynamic simulations. Therefore, this study is established a relatively realistic model of the posterior urethra based on MRI data combined with the urodynamic data of patients and analysed the urodynamic characteristics of the posterior urethra model after benign prostatic hyperplasia (BPH) surgery using a CFD dynamic simulation.

METHODS

Based on clinical MRI data, a three-dimensional real urethral model was established for two patients with BPH after surgery. The boundary conditions were set according to the patients' real urodynamic data, and a Reynolds averaged Navier‒Stokes model was used for transient simulations. The dynamic simulation depicted the entire urination process, and the urine flow characteristics were studied under real urethral morphology after surgery.

RESULTS

1. By comparing the three-dimensional trajectory of urine and the vortex identification cloud map based on the Q criterion, we intuitively observed the distribution of the vortex in the model, and a 'gourd-shaped' urethra was more likely to generate a vortex than a 'funnel-shaped' urethra. 2. After surgery for BPH, the changes in the posterior urethral pressure were mainly concentrated in the urethral membrane, and the velocity increased while the pressure decreased. The curve of the posterior urethral pressure changes during urination was simulated and calculated. The posterior urethral pressure gradients of the two patients were 6.6 cmH2O and 5.26 cmH2O.

CONCLUSIONS

The complete urinary discharge process can be dynamically simulated using CFD techniques. By comparing the simulation results, the posterior urethral morphology can have an important impact on the urinary flow characteristics. Determining the location of vortex generation can lay a foundation for personalized surgical plans for patients in the future. Furthermore, numerical simulations can provide a new method for the study of non-invasive posterior urethral pressure gradients.

Transperineal pelvic floor ultrasound in male

INTRODUCTION

The pelvic floor (PF) is a highly complex structure which may be affected by various stimulating factors like decreased PF support. As ultrasound can dynamically observe the position and mobility of anatomical structures, However, there are very few studies on PF ultrasound in males.

MATERIALS AND METHODS

Twenty-one male patients with normal conditions underwent transperineal pelvic floor ultrasound (TPFU) examination. Ultrasound was performed in a supine lithotomy position. The probe was pressed on the sagittal plane of the perineum and adjusted till the anorectal angle, as well as bladder, were located and the median prostate and pubic symphysis were visible on the sagittal plane. TPFU was carried out to observe the patterns of pelvic floor movement during different phases, measure ultrasound parameters of the PF in men, and assess the potential applications and prospects of the male PF.

RESULTS

Two-dimensional male PF ultrasound can detect the bladder, prostate, male urethra, anus, rectum. Resting, Valsalva, and contraction phases of the PF are clearly shown, the pelvic organs in the Valsalva phase shift to the dorsal foot side, and shift to the cephalic ventral side when the levator ani muscle (LAM) contracts. Three-dimensional male PF ultrasound can visually show the shape and structure of the levator ani muscle hiatus.

CONCLUSION

It is a feasible examination tool for detecting PF disorders. However, there are still many fields to explore in the future.

Why upright standing men urinate more efficiently than in supine position: A morphological analysis with real-time magnetic resonance imaging

PURPOSE

Few studies have examined the effects of body position on urination efficiency morphologically. We aimed to dissect out the anatomical changes of pelvic organs during urination in the upright and supine positions by a real-time magnetic resonance imaging (rtMRI) system.

METHODS

Thirteen healthy male volunteers aged 26-60 years were included in the study. The sagittal real-time two-dimensional images were taken to evaluate urinary efficiency, along with change in six morphological indices at the time of storage and the beginning of voiding, in both upright ant supine positions.

RESULTS

Urination was more efficient in upright position than in supine position, as expressed by higher average rate of bladder emptying (9.9 ± 4.2 vs. 6.8 ± 2.9 ml/s, p < 0.05) and also by fewer participants showing significant residual urine (1/13 vs. 7/13, p < 0.05). At the onset of voiding in standing position, the levator ani (LA) muscle moves downward and backward followed by descent of the bladder neck and rotation of the prostate around the symphysis. Such changes were expressed by two morphological indices. One was posterior vesicourethral angle at the start of voiding, 152 ± 7 versus 140 ± 1 in upright and supine position (p < 0.05). The other index was the change in angle between the LA line and pubo-coccygeal line in upright and supine position, 9.4 ± 9.9 versus 1.6 ± 7.9 before voiding (p < 0.05) and 30.2 ± 14.0 versus 17.3 ± 12.9 after the start of voiding (p < 0.05).

CONCLUSION

The dynamic relaxation of LA seemed to be a key movement that enables more efficient urination in standing position than in supine position.

A pilot study of bladder voiding with real-time MRI and computational fluid dynamics

Lower urinary track symptoms (LUTS) affect many older adults. Multi-channel urodynamic studies provide information about bladder pressure and urinary flow but offer little insight into changes in bladder anatomy and detrusor muscle function. Here we present a novel method for real time MRI during bladder voiding. This was performed in a small cohort of healthy men and men with benign prostatic hyperplasia and lower urinary tract symptoms (BPH/LUTS) to demonstrate proof of principle; The MRI urodynamic protocol was successfully implemented, and bladder wall displacement and urine flow dynamics were calculated. Displacement analysis on healthy controls showed the greatest bladder wall displacement in the dome of the bladder while men with BPH/LUTS exhibited decreased and asymmetric bladder wall motion. Computational fluid dynamics of voiding showed men with BPH/LUTS had larger recirculation regions in the bladder. This study demonstrates the feasibility of performing MRI voiding studies and their potential to provide new insight into lower urinary tract function in health and disease.

Exploring pelvic floor muscle activity in men with lower urinary tract symptoms

Aim

We aimed to explore the utility of the Multiple Array Probe Leiden (MAPLe) device to assess pelvic floor muscle activity in men with lower urinary tract symptoms (LUTS).

Methods

This was an observational cohort study performed at the urology outpatient department of a large teaching hospital in the Netherlands between April and October 2018. We recruited male patients referred for the assessment of LUTS, without a history of prostate surgery, if they had an International Prostate Symptom Score greater than or equal to 8. The MAPLe device was then used to assess the puborectalis, pubococcygeus, iliococcygeus, urogenital diaphragm, and the internal and external anal sphincters during three tasks: a rest period (1 minute), five maximum voluntary contractions (held for 3 seconds each), and three maximal endurance contractions (held for 15 seconds each).

Results

In total, 57 patients were included, 5 of which had diabetes mellitus. Muscle activity at rest was significantly lower than during either contraction task and did not differ between the muscle groups. By contrast, the external anal sphincter had significantly less activity than any other muscle group during the endurance task, and the internal anal sphincter and puborectalis had significantly less activity during the maximum voluntary contraction task. No association was found between pelvic floor muscle activity and LUTS severity during any task.

Conclusion

Pelvic floor muscle activity and LUTS severity appear to be unrelated, but this does not completely exclude the possibility of muscle involvement in the development or experience of symptoms. Further research is needed.

MRI of the Male Pelvic Floor

The pelvic floor is a complex structure that supports the pelvic organs and provides resting tone and voluntary control of the urethral and anal sphincters. Dysfunction of or injury to the pelvic floor can lead to gastrointestinal, urinary, and sexual dysfunction. The prevalence of pelvic floor disorders is much lower in men than in women, and because of this, the majority of the published literature pertaining to MRI of the pelvic floor is oriented toward evaluation of the female pelvic floor. The male pelvic floor has sex-specific differences in anatomy and pathophysiologic disorders. Despite these differences, static and dynamic MRI features of these disorders, specifically gastrointestinal disorders, are similar in both sexes. MRI and MR defecography can be used to evaluate anorectal disorders related to the pelvic floor. MRI can also be used after prostatectomy to help predict the risk of postsurgical incontinence, to evaluate postsurgical function by using dynamic voiding MR cystourethrography, and subsequently, to assess causes of incontinence treatment failure. Increased tone of the pelvic musculature in men secondary to chronic pain can lead to sexual dysfunction. This article reviews normal male pelvic floor anatomy and how it differs from the female pelvis; MRI techniques for imaging the male pelvis; and urinary, gastrointestinal, and sexual conditions related to abnormalities of pelvic floor structures in men.Online supplemental material is available for this article.^©RSNA, 2019.

Correlation between prostatic urethral angulation and symptomatic improvement after surgery in patients with lower urinary tract symptoms according to prostate size

PURPOSE

To investigate the effect of prostate anatomical factors on the changes in lower urinary tract symptoms (LUTS) and uroflowmetric values after surgery.

METHODS

The medical records of 448 patients who underwent transurethral resection of the prostate (TURP) from January 2006 to December 2018 were analyzed retrospectively. Changes in the International Prostate Symptom Score (IPSS), maximum flow rate (Qmax), and post-void residual urine volume (PVR) at 3 months after TURP were evaluated. Prostate volume, intravesical prostatic protrusion (IPP), and prostatic urethral angulation (PUA) were measured using transrectal ultrasonography, and their effect on the changes in LUTS after TURP was analyzed using multivariable linear regression.

RESULTS

Among patients with prostate volume < 50 mL, preoperative IPSS total score (IPSS-t), voiding symptom score (IPSS-vs), and storage symptom score (IPSS-ss) were significantly better in patients with a smaller PUA (< 51°) than in those with a larger PUA (≥ 51°) (p = 0.001, < 0.001, and 0.020, respectively). Changes in IPSS-t, IPSS-vs, IPSS-ss, and PVR at 3 months after TURP were significantly correlated with PUA (p ≤ 0.001, < 0.001, 0.048, and 0.012, respectively). Multivariable linear regression revealed PUA to be independently associated with changes in IPPS-t and IPSS-vs (p = 0.025 and < 0.001, respectively) only in patients with prostate volume < 50 mL.

CONCLUSION

Prostatic urethral angulation was significantly associated with postoperative changes in LUTS only in patients with small prostate, and had no clinical significance in patients with large prostate. In patients with small prostate and large PUA, surgery should actively be considered.

Direct mechanical characterization of prostate tissue-a systematic review

BACKGROUND

Direct mechanical characterization of tissue is the application of engineering techniques to biological tissue to ascertain stiffness or elasticity, which can change in response to disease states. A number of papers have been published on the application of these techniques to prostate tissue with a range of results reported. There is a marked variability in the results depending on testing techniques and disease state of the prostate tissue. We aimed to clarify the utility of direct mechanical characterization of prostate tissue in identifying disease states.

METHODS

A systematic review of the published literature regarding direct mechanical characterization of prostate tissue was undertaking according to PRISMA guidelines.

RESULTS

A variety of testing methods have been used, including compression, indentation, and tensile testing, as well as some indirect testing techniques, such as shear-wave elastography. There is strong evidence of significant stiffness differences between cancerous and non-cancerous prostate tissue, as well as correlations with prostate cancer stage. There is a correlation with increasing prostate stiffness and increasing lower urinary tract symptoms in patients with benign prostate hyperplasia. There is a wide variation in the testing methods and protocols used in the literature making direct comparison between papers difficult. Most studies utilise ex-vivo or cadaveric tissue, while none incorporate in vivo testing.

CONCLUSION

Direct mechanical assessment of prostate tissue permits a better understanding of the pathological and physiological changes that are occurring within the tissue. Further work is needed to include prospective and in vivo data to aid medical device design and investigate non-surgical methods of managing prostate disease.

Adreno-muscarinic synergy in the male human urinary outflow tract

AIM

To examine putative interaction between adrenergic and muscarinic contractile activation in the human urinary outflow tract.

METHODS

Tissue from the trigone and prostatic urethra was obtained from 12 cystectomy and 16 prostatectomy specimen. Contractions were elicited by exposure to exogenous agonists before and after inhibition of Rho kinase and protein kinase c (PKC). Immunofluorescence and Western-blot studies were performed using antibodies to muscarinic M3-receptors (M3-R) and alpha1A-adrenoreceptors (alpha1A-AR). The study is registered with ClinicalTrials.gov, number NCT01227447.

RESULTS

There was strong co-localization of M3-R and alpha1A-AR on trigonal and urethral myocytes. Western blot analysis revealed a significantly higher expression of alpha1A-AR in the superficial than in the deep trigone. Phenylephrine (PE, 1 μm) augmented contractions induced by carbachol (CA, 3 μm) to more than threefold control in the male superficial trigone, and to about sevenfold control in the proximal urethra. No such potentiation could be detected in female bladder outlet. Both PKC inhibitor GF 109203X and Rho kinase inhibitor Y-27632 reduced responses to 1 μM PE as well as to 3 μM CA significantly. However, the synergistic effect of the combined intervention remained proportionally unaffected.

CONCLUSIONS

Muscarinic and adrenergic receptor activation exerts a strong synergistic effect in the male human bladder trigone and proximal urethra.

Displacement patterns of stranded I-125 seeds after permanent brachytherapy of the prostate: Dosimetry in the operating room put into perspective

BACKGROUND AND PURPOSE

The reliability of post-implant dosimetry in the OR depends on the geometrical variability of implant and anatomy after the procedure. The purpose was to gain detailed information on seed displacement patterns in different sectors of the prostate.

MATERIALS AND METHODS

Of 33 patients with stranded seed implants the seed geometry and the dose distribution were compared between the situation in the OR just after the procedure, based on ultrasound images, and the situation after 1month, based on registered CT and MR images.

RESULTS

There was a substantial displacement of ventral seeds of 3.8±2.5mm in caudal direction (p<0.001). Of these ventral seeds cranially located seeds moved more than caudally located seeds, 4.5±2.7mm and 2.9±2.6mm, respectively (p<0.001). The D₉₀ in the dorsal-caudal and ventral-caudal sectors increased with respectively 44±20Gy and 29±28Gy (p<0.001) and decreased with 17±31Gy in the ventral-cranial sector (p=0.008).

CONCLUSIONS

There were substantial changes in dose distribution 1month after the procedure, mainly due to implant and prostate shrinkage and displacement of ventral seed strands in caudal direction. When performing dynamic dosimetry or dosimetry at the end of the procedure the effect of these phenomena has to be taken into account when using stranded seeds.

MRI evaluation of benign prostatic hyperplasia: Correlation with international prostate symptom score

PURPOSE

To investigate the correlation between magnetic resonance imaging (MRI)-derived prostate parameters and benign prostatic hyperplasia (BPH) type with the International Prostate Symptom Score (IPSS).

MATERIALS AND METHODS

In all, 61 patients (median age, 60; range, 41-81 years) who underwent preoperative MRI and prostatectomy were included in this retrospective study. The MRI-based parameters including total prostate volume (TPV), transition zone (TZ) volume (TZV), TZ index, intravesical prostatic protrusion (IPP), the anterior fibromuscular stroma (AFMS) distance, prostatic urethral angle, bladder wall thickness, urethral wall thickness, urethral compression, urethral wall changes, and BPH type were correlated with total IPSS, IPSS-storage symptom (IPSS-ss), IPSS-voiding symptom (IPSS-vs), and responses to the individual IPSS questions using Spearman (ρ) or Pearson (r) correlation coefficients, one-way analysis of variance (ANOVA), and multiple linear regression.

RESULTS

TPV (r = 0.414, P = 0.001), TZV (r = 0.405, P = 0.001), IPP (r = 0.270, P = 0.04), and AFMS distance (r = 0.363, P = 0.004) correlated with total IPSS. In multiple linear regression analysis, TZV was the only predictor for total IPSS (P = 0.001), IPSS-ss (P < 0.001), IPSS-vs (P = 0.03), and the scores for the IPSS questions 1 (P = 0.03) and 4 (P = 0.001). TPV was a predictor of the scores for questions 2 (P = 0.003), 3 (P = 0.009), and 7 (P < 0.001).

CONCLUSION

Several MRI-derived prostate measurements (TPV, TZV, IPP, AFMS distance) correlated with total IPSS. TZV was the only predictor for total IPSS based on multiple regression analysis.

LEVEL OF EVIDENCE

3 J. Magn. Reson. Imaging 2017;45:917-925.

[Diagnosis and surgical treatment of postprostatectomy stress incontinence: recommendation of the working group Urologische Funktionsdiagnostik und Urologie der Frau]

Today, for the surgical treatment of postprostatectomy incontinence, several treatment options are available, e.g., adjustable and functional sling systems, artificial sphincter, bulking agents, and balloons. However, no recommendations in terms of specific diagnostic tools and differentiated treatment options for everyday life are available. Our aim is to provide some clinically relevant recommendations for the necessary diagnostic workup and different treatment options of postprostatetectomy incontinence to support clinical decisions in everyday life. Treatment selection should be based on contraindications. However, there is a broad overlap of the various surgical options.

Is a wider angle of the membranous urethra associated with incontinence after radical prostatectomy?

PURPOSE

To investigate whether differences in the anatomy and dynamics of the pelvic floor (PF) in patients after radical prostatectomy (RP) depicted on magnetic resonance imaging (MRI) are associated with continence status.

METHODS

In the prospective designed study, 24 patients with post-prostatectomy stress urinary incontinence were enrolled. Additionally, 10 continent patients after RP were matched for age, body mass index and perioperative parameters. All patients underwent continence assessment and MRI (TrueFISP sequence; TR 4.57 ms; TE 2.29 ms; slice thickness 7 mm; FOV 270 mm) 12 months after RP. Images were analyzed for membranous urethra length (MUL), angle of the membranous urethra (AMU), severity of periurethral/urethral fibrosis, lifting of the levator ani muscle, lowering of the posterior bladder wall (BPW), bladder neck (BN) and external urinary sphincter (EUS), and symphyseal rotation of these structures during the Valsalva maneuver and voiding.

RESULTS

Compared to continent controls, incontinent patients showed a significant wider AMU during voiding (p = 0.002) and more pronounced lowering of the BN and EUS (p < 0.001). No differences between the groups were found in symphyseal rotation of the analyzed structures, MUL and severity of periurethral/urethral fibrosis.

CONCLUSIONS

The angle of the membranous urethra as a result of anchoring of the BN and EUS in the PF appears to be an important functional factor with an essential impact on continence after RP. Functional MRI seems to be a helpful imaging tool for morphologic and dynamic evaluation of the PF.

[Imaging diagnostics of the male pelvic floor]

The understanding of the female pelvic floor during the last 20 years was very much influenced by the new techniques of sonographic and magnetic resonance imaging (MRI). Functional imaging of the male pelvic floor is, however, still in its infancy. In analogy to ultrasound examinations of the female pelvic floor, perineal ultrasound can be also be applied to men. The mobility of the proximal urethra, scarring of the bladder neck or implanted suburethral meshes can be easily visualized. Studies on healthy men provide information about different muscular structures during micturition. Morphology and function of the external sphincter can be visualized with transrectal or intraurethral ultrasound and also with a perineal approach. Using functional MRI the complex interactions of bladder, urethra, external sphincter and pelvic floor muscles can be evaluated. Functional MRI is so far not generally available but enables a better understanding of the function of the male pelvic floor. Imaging of the male pelvic floor makes a substantial contribution for improving surgical procedures for male incontinence in the future.

Ultrasound-triggered BSA/SPION hybrid nanoclusters for liver-specific magnetic resonance imaging

Nanoclusters of superparamagnetic iron oxide nanoparticles (SPION) are developed for liver-specific magnetic resonance imaging (MRI) by a unique synthesis route. The process is efficient, environmentally benign, and straight forward within five minutes. The clustering effect is triggered in the presence of bovine serum albumin (BSA) aqueous phase under ultrasonication condition. The hydrophobic SPION are densely self-assembled into BSA/SPION hybrid nanoclusters with a uniform size of ~86 nm. The as-prepared BSA/SPION hybrid nanoclusters are found to be biocompatible and stable. They exhibit high transverse relaxivity and longitudinal relaxivity in water (r(2) and r(1) values are 600.8 and 4.3 s(-1) per mM of Fe(3+), respectively). In vivo T(2)-weighted MRI shows excellent enhancement in liver with an imaging time-window up to 48 h. In vivo biodistribution study indicates a gradual excretion of the nanoclusters via hepatobiliary (HB) processing. No toxicity is observed in the in vivo and ex vivo experiments. The BSA/SPION hybrid nanoclusters present great potential in MRI as the liver-specific contrast agents (CAs).