Defaecation disorders, such as intussusception, rectocele, enterocele and pelvic organ prolapse, severely impact the quality of life of sufferers and incur a significant economic burden on health services [1]. Due to age and prior history of multiple instrumented or vaginal deliveries, nearly 50% of multiparous women aged more than 50 years suffer from some form of pelvic floor disorder [2]. In the UK, a survey by the Royal College of Obstetricians and Gynaecologists on two thousand women reported that over 60% of women have at least one symptom of poor pelvic floor health, with 69% not having spoken about their pelvic floor health to anyone in the NHS [3]. In the USA, nearly 25% of women receive a diagnosis of pelvic floor disorder, and approximately 200,000 women undergo surgery every year [4]. Patients typically present with complaints/symptoms of faecal incontinence, pain during defaecation, chronic constipation, abnormal urination, sphincter defects, or sexual dysfunction [1, 4, 5].

Imaging of the rectum is an important component of the conventional clinical assessment of pelvic floor disorder and subsequent surgical planning. The two main techniques used routinely are fluoroscopic proctography or supine magnetic resonance imaging (MRI) defaecography. Fluoroscopic proctography involves collecting a series of X-rays during defaecation after administering barium contrast per rectum (and often orally to outline the small bowel). As X-ray imaging is a planar imaging tool, fluoroscopic proctography cannot image all three pelvic floor compartments at one time; it only images the luminal aspect of the bowel wall [6]. Thus, it is less sensitive at detecting abnormalities in the anterior pelvic compartment e.g., the urinary bladder, caused by general pelvic floor weakness [5]. Moreover, it involves a significant level of ionising radiation exposure [5, 7] for women of child-bearing age [1] with a mean effective dose of 4.9 mSv [8].

Contrary to X-ray-based techniques, MRI involves no ionising radiation and, therefore, has no potential detrimental effects to future health. Moreover, it allows superior temporal and spatial resolution as well as imaging in multiple planes [8] with superior contrast to enable better delineation of the pelvic floor anatomy. However, conventional supine MR-based defaecating proctography (sMRDP) involves patients attempting to push out a gel from their rectums whilst lying down; patients find it difficult and uncomfortable to carry out the voiding phase, which reveals the most clinically relevant information [1]. In addition, due to this abnormal posture, the process fails to mimic the normal structural or functional changes of the pelvic floor during defaecation [9], partially limiting the clinical/diagnostic value of sMRDP. For example, fluoroscopic proctography is more sensitive than MRDP in detecting rectal intussusception, a condition where the bowel wall folds in on itself during defaecation [9]. A study has shown that only 50% of patients were able to push out an artificial stool when lying down compared to 80% when sitting up [10].

Upright MRDP (uMRDP) with an open configuration magnet allows patients to defaecate in their regular seated posture. Thus, it mitigates the limitations of sMRDP and enables clinicians to visualise anorectal morphology and functional changes of the complete pelvic floor while patients are defaecating in their typical upright posture.

Many previous studies have investigated the prospects of uMRDP and compared its utility to fluoroscopic proctography, but not without limitations related to patient comfort, image quality, and/or resolution for capturing dynamic details. For example, many used T1-weighted imaging to suppress water contrast, which results in poor imaging of the bladder and bowel. They enhanced contrast by mixing gadolinium-based contrast agent (GBCA) with rectal paste (i.e., ultrasound gel, mashed potatoes, etc.) [1, 5,6,7,8], but gadolinium contrast carries the risks of allergic reaction and involves the additional cost and environmental impact of GBCA [11]. Many studies have also used urethral catheters or placed markers in the vagina and/or rectum to optimise their data quality [1, 8, 12,13,14,15], but such methods are invasive, may be uncomfortable, and could increase the risk of infection. Moreover, the existing radio-frequency (RF) coils for typical uMRDP imaging might not give dedicated coverage to the pelvic floor areas, limiting image quality. Coils strapped around the pelvis might cause discomfort and intervene with the natural manoeuvres during defaecation [7, 8]. Therefore, alternative imaging sequences and a comfortable RF coil structure with suitable coverage should improve the efficacy of the technique.

In this study, we use a 0.5 T ASG Open MR scanner with a purpose-built RF commode coil and optimised T2-w acquisition protocol to propose a safe and comfortable method of performing uMRDP in the sitting position. The commode system with integrated RF coils substitutes the strapping of coils around the pelvis and ensures comfort as well as uninterrupted pelvic floor movement during defaecation. The T2-w dynamic sequence aims to provide sufficient contrast without invasive GBCA injection into the vagina, urinary bladder or small bowel. Our aim is three-fold: first, to investigate the feasibility of the equipment and sequences for imaging seated defaecation in healthy volunteers; second, to assess the quality of the dynamic data for extracting the conventional anatomical and functional metrices used for clinical assessments; finally, to evaluate the inter-rater and intra-rater variability in pelvic floor metrices, as extracted by two expert Radiologists.