Value of bowel preparation techniques for prostate MRI: a preliminary study

Multiparametric MRI (mpMRI) has become an invaluable tool in assessment of men at risk for prostate cancer [1, 2]. Superior MRI image quality (IQ) is indispensable for the radiologist to deliver an accurate diagnosis [3]. The importance of scan quality for prostate cancer detection is reflected in the recent development of a new scoring system for the evaluation of multiparametric prostate MRI IQ, the Prostate Imaging Quality (PI-QUAL) score [4], which rates diagnostic quality by means of technical and visual assessment criteria. Scan quality can be impaired by artifacts, such as motion or susceptibility. Several patient preparation techniques have been proposed to mitigate those artifacts [5‐7].

Motion artifacts can lead to ghosting, blurring and a reduced signal-to-noise ratio, particularly in images with a long scan time, like T2-weighted images [8, 9]. A superior IQ is particularly valuable for discerning fine anatomical structures, for example the border of nodules within the transitional zone when differentiating between a PI-RADS 2 and 3 score [10]. In this context, antispasmodic agents such as hyoscine N-butylbromide (HBB) are widely used for suppression of bowel peristalsis. However, study results regarding the use of HBB are equivocal, as some authors did find positive effects on artifact reduction and/or IQ [7, 11], while others did not [9, 12].

Gas or stool may distend the rectum, introduce susceptibility artifacts and deform the dorsal prostate contour through geometric distortion [13, 14]. This issue may be particularly unfavorable, as the majority of prostate carcinomas arise within the peripheral zone [15]. Diffusion-weighted imaging (DWI) suffers most from these types of artifacts, notably at higher field strengths [16]. Hence, measures to evacuate the rectum before the MRI exam seem reasonable. Studies investigating the use of a preparatory microenema (ME) before scanning revealed that stool/gas and related artifacts in DWI can be reduced significantly [17, 18]. Lim et al. [19] even showed that the amount of stool correlates positively with motion artifacts on T2w. However, the effect either does not [19] or only modestly translate into better IQ itself [18], indicating the complexity of the topic, as solely emptying the rectum or reducing artifacts does not seem to be sufficient. Imposing fasting measures prior to the MR scan is another hypothesis on how to reduce bowel peristalsis. However, the topic has not been investigated extensively up to date. The discrepancy of the results in the literature on HBB and ME most likely explains why there was no consensus reached regarding this topic in current guidelines such as the “Prostate Imaging and Reporting Data System (PI-RADS) v2.1” (10). Finally, despite the fact that HBB and ME are very often used simultaneously, no study investigated the effect of those techniques in combination or the specific contribution of one intervention alone regarding IQ in prostate MRI.

Therefore, the purpose of this study was to investigate the value of HBB, ME, DR in combination and alone for artifact reduction and IQ in prostate MRI.

In our study, ME had a positive impact on reducing artifacts and improving IQ. Antispasmodic pre-medication with HBB and DR or combinations thereof appear to show no positive or synergic effect.

Bowel peristalsis may induce movement of pelvic organs, eventually leading to artifacts depending on the direction of k-space sampling [8, 9]. Our study results showed no benefit with HBB, neither when used exclusively, nor in combination with ME and or DR. We observed a positive trend toward better delineation of anatomic detail and less motion artifacts on T2w sequences for R1 only; however, the difference was not statistically significant. These results are in line with Wagner [9] and Roethke et al. [12]. Still, the data must be interpreted with caution due to comparably lower field strength (1.5T) used by Wagner et al. [9] in their study setting. Roethke et al. [12] assessed IQ parameters on the level of the whole MRI exam, and not based on a single sequence. There are two studies [7, 11] which are methodologically and technically similar to our study setup, demonstrating higher IQ and lower motion-related artifacts with HBB in T2w images. This might in part be explained by a different dose compared to our study setup. While we injected 20 mg of HBB, Slough [11] and Ullrich et al. [7] used a dose of 40 mg. However, despite intense pharmacodynamic and -kinetic investigation of the effects of HBB on bowel peristalsis [21], it is still not clearly established whether to use 20 or 40 mg in prostate imaging. Some MRI and CT studies suggest that the injection of 20 mg i. v. may be sufficient [8, 22‐24]. Also results from a CT colonography study confirm that 20 mg of HBB i. v. significantly improved colonic distension without further improvement when increasing the dose to 40 mg [25]. Furthermore, empirically raising the dose to 40 mg HBB remains problematic due to associated side-effects, which may be significantly underestimated, as reported by Johnson et al. [8]. To summarize, whether the dose of 20 mg gives a sufficient explanation for the discrepancy of the available data remains unclear. We excluded patients with contraindications such as a history of glaucoma, severe urinary retention and cardiac arrythmia. However, studies have reported that it might be feasible to acknowledge only unstable cardiac disease as a contraindication and instead brief patients in advance about potential ocular symptoms, so they can seek medical help in the case of symptoms. This is due to the fact that particularly patients with new/undiagnosed cases of glaucoma have been described to be those truly at risk of acute angle glaucoma [26]. Hence, HBB side-effects might only be relevant to a small minority of patients. Based on (i) a superior potency for suppression of bowel peristalsis and (ii) a more favorable side-effect profile due to a lack of anticholinergic properties, glucagon may be a viable alternative [27]. Gutzeit et al. reported the best efficacy and longest duration of bowel peristalsis suppression for a combination of intramuscularly injected HBB and i. v. injected Glucagon, allegedly due to synergistic effects [28].

The bowel is subject to spontaneous phasic activity [29] which may be amplified by ingestion of food/coffee through initiation of propulsive peristaltic waves. Theoretically, fasting prior to the MRI exam should reduce this activity. However, in our study setting imposed DR did not add incremental value to (i) HBB alone or (ii) HBB and ME combined. Moreover, Reader 2 rated IQ in the HBB+/ME−/DR+ cohort significantly worse, as compared to the cohort using ME in combination with DR or with HBB and DR combined. Nevertheless, as bowel peristalsis may be influenced through different interacting mechanisms, the authors believe that—despite not reaching statistical significance—inhibition of bowel peristalsis may still be useful in prostate MRI, as also indicated by Roethke et al. [12].

Rectal distension through stool or gas has been shown to significantly increase geometric distortion of the prostate gland [14]. This effect is particularly pronounced in echoplanar imaging (EPI) and on higher field strengths [8, 9]. Two studies [17, 18] demonstrated that ME may reduce gas-related artifacts significantly in DWI. Our data confirms these results. However, while Coskun et al. [18] found only moderately positive effects in terms of artifact reduction in one of two readers, our results show stronger evidence in support of ME. The increase in DWI IQ translated into significantly better perception of overall IQ of the whole mpMRI exam and logistic regression analysis revealed ME as the single significant predictor of ‘good’ whole MRI IQ. Using ME before prostate MRI increased the chance for having ‘good’ whole MRI IQ by almost 3 times independently in both readers (OR R1, 2.98 and R2, 2.73). In line with our results, Lim et al. [19] found less stool in patients who used ME and the amount of stool did correlate with motion artifacts on T2w. However, DWI IQ did not improve with the use of ME. This is perhaps rooted in the low study power [19], as only a minority of patients in their study (n = 32) in the non-enema group had moderate or large amounts of stool, as opposed to our corresponding patient cohort (mean stool score 2.44/3). In addition, we observed a positive effect of ME on rectal evacuation independently of the concurrently used HBB and/or DR. According to the available literature, ME seemingly has a positive effect on rectum evacuation and it has the potential to significantly decrease susceptibility artifacts on DWI [5, 17]. Yet, it does not exert enough effect on bowel peristalsis in order to improve IQ in T2w. ME is generally safe and easy to use. However, self-administration in a hospital setting on-site before the MR exam might be stressful, leading to unsuccessful application and hence increasing the risk of incomplete bowel preparation. Administrating ME prior to the MR exam at home might be a way (i) for increasing the probability for a technically successful application and (ii) ensuring that ME can fully take effect before the scan. We acknowledge that there may be alternative approaches for artifact reduction [10]. However, ME is a bowel preparation technique for which available data (i) clearly indicates a positive effect on reduction of bowel peristalsis [18], (ii) strongly suggests improvement of DWI quality [5], (iii) where practically no side-effects are expected [30] and (iv) costs of the intervention are very low [5].

We recognize the following limitations. The patient count per cohort results in a moderate study power compared to some of the abovementioned studies [7, 11, 18]. When DR were introduced into clinical routine, HBB was already implemented, hence cohort/s of patients without HBB in combination with DR were not available. Moreover, when assessing the value of DR, a meaningful comparison was only possible between cohorts 3/3F and 4/4F, as otherwise > 1 parameter would have been altered between the cohorts and attribution of an observed effect to one of the bowel preparation techniques would be difficult. Finally, this study has investigated parameters of IQ between patients receiving different bowel preparation techniques. Therefore, studies investigating diagnostic accuracy will possibly put the potential benefits of bowel preparation techniques into perspective.