Patients with claustrophobic anxiety, who are more likely to be frightened during MR imaging, have been reported to experience claustrophobia in up to 35% of all examinations . To complete the scan, conscious sedation and additional sequences (after sedation) may be necessary in these patients. This situation involves significant risks of adverse events [7–9] and is associated with additional costs because it reduces workflow, limits patient acceptance, and wastes valuable scanning time and thus induces costs. On the other hand, prematurely terminated scans as well mean an important financial loss for the health care system. Improved patient comfort during MR imaging (mainly reduction of noise and sensation of confinement) appears to be essential to avoid claustrophobic reactions [10, 11].
A more patient-centered design of closed MR systems is one effective approach to make MR imaging more comfortable for patients. Few studies have investigated patient acceptance and the potential to reduce claustrophobic anxiety of recent closed MR scanners with noise reduction and short- and wide-bore design in comparison to conventional MR scanners.
In a large cohort study of 55,734 outpatients, Dewey et al. assessed the potential to reduce claustrophobia of a recent 1.5-T MR scanner with 97% noise reduction and a short- and wide-bore design . Patients were examined on either the recent or a conventional MR scanner. The recent MR scanner was shown to reduce claustrophobia by a factor of 3, although there were more head-first examinations on that scanner. Intraindividual comparisons of patients who underwent imaging on both MR units showed similar results with a claustrophobia rate of below 1% .
In a retrospective study on the occurrence of claustrophobia in 5,682 patients examined on either a 1.5-T closed MR scanner or a 0.5-T noise-reduced MR scanner with a short and wide bore Dantendorfer et al. found no significant difference between the two MR units . However, there was a selection bias because staff was referring highly anxious patients to the recent MR scanner. Thus, the authors conclude that the short-bore MR scanner may in fact reduce claustrophobia . In a later study by Dantendorfer et al., 297 patients without MR imaging experience were randomly examined on either a 1.5-T closed MR scanner or a recent 0.5-T noise-reduced MR scanner with a short and wide bore . Anxiety before and after the scan was among others assessed using the State questionnaire of the STAI. Although patients felt more at ease in the recent MR scanner (concerning noise and confinement), there was no significant difference in patient acceptance and occurrence of motion artifacts. Interestingly, there was no correlation between STAI scores and motion artifacts, but patients who were more concerned about the technical apparatus had more motion artifacts .
Another approach to improve patient acceptance of MR imaging is a more open vertical scanner configuration, although until recently such systems operated at rather low field strengths (0.2 T), resulting in poor image quality.
Heuck et al. compared two high-field closed MR systems operating at 1.5-T and 1.0-T with an open whole-body scanner and a dedicated extremity MR system, both operating at 0.2-T . In 40 patients examined on each system (160 total) they found a mainly positive condition and acceptance for all MR scanners. However, patients who were examined on the open MR scanners felt significantly more confident and calm, despite longer examination durations. Patients' suggestions for improvement of the high-field closed MR systems mainly concerned reduction of noise and enlargement of the bore. Nevertheless, these authors concluded that the necessary technical conditions and not differences in patient preference should be crucial for the choice of an MR system .
In a recent pilot study Bangard et al. have examined 36 claustrophobic and 36 non-claustrophobic patients on a recently introduced open MR scanner with high-field strength (1.0 T) . Anxiety was assessed using validated questionnaires (STAI, CLQ, MRI FSS ). In the claustrophobic patients scan termination rate was reduced to 8% compared to 58.3% in previous examinations on conventional MR systems, and 91.7% preferred the open MR scanner. Furthermore, claustrophobia did not reduce image quality by motion artifacts .
A 0.5-T interventional MR scanner with a vertical gap in the bore of the magnet ("double donut") was used in a study by Spouse et al. . 96% of 50 claustrophobic patients who were unable to complete a conventional MR scan successfully underwent MR imaging on the interventional scanner. Patients reported less anxiety than during their previous MR imaging and felt significantly better informed about the procedure. However, friends or relatives were allowed to stay in the magnet room and many patients indicated that this, beside the scanner design, had helped them considerably .
In contrast to the above mentioned studies, the CLAUSTRO trial will directly compare an open MR scanner with a vertical 1.0-T magnetic field, and a closed noise-reduced MR scanner with a short- and wide-bore design and 1.5-T field strength in regards to claustrophobia and image quality as well as influence on further clinical management in a randomized controlled trial. Patients included will have at least moderate levels of claustrophobic anxiety, experienced claustrophobia during a prior MR imaging or rejected a current scheduled MR imaging due to claustrophobia, and will have a clinical indication for MR imaging and will thus be at high risk to experience claustrophobia during the MR scan. Anxiety will be assessed before and after MR imaging as well as 4-6 weeks and 7 months after the scan in order to address the development of claustrophobia. Increase of claustrophobic anxiety has been found if the scan is terminated prematurely or high anxiety is tolerated [26, 38–40]. On the other hand, there are reports of decreased anxiety after completed MR imaging [40, 41]. Long-term alleviation of claustrophobia after completed MR imaging might support the potential of exposure therapy to treat claustrophobia [42, 43]. To perform the comparison of image quality as reliable as possible the anatomical regions to be examined will be limited to head, spine and shoulder, and equal sequences on both scanners with comparable voxel sizes will be utilized. Diagnostic utility and clinical outcome will be assessed 7 months after MR imaging which is an appropriate time-frame to detect an influence on clinical management. Of course this will be mediated through the patients and referring physicians' response to MR results. Furthermore, the study will address which specific scanner design is evaluated by patients to be the most attractive and which further improvements in designing MR scanners should be followed by manufacturers. Randomization will be done as the most decisive evidence for judging the efficacy of diagnostic tests comes from randomized comparisons in which the controlled design obviates the biases of observational studies [15, 16]. Patients who are assigned to imaging in one MR scanner but cannot bear this procedure due to claustrophobic anxiety will be cross-referred to imaging in the other scanner in order to preclude adverse events associated with sedation [7–9]. This will also allow direct comparison of the two options in those patients as an ancillary study. Due to its design this trial will also be able to analyze and compare the cost-effectiveness of the two MR scanners.
Anxiety during MR imaging can occur due to several other psychosomatic or psychiatric disorders than claustrophobia e.g., panic disorder, adjustment disorder with anxious mood, or major depression . Within the limits of the study, claustrophobia will not be diagnosed according to ICD-10 or DSM-IV criteria [28, 44]. Furthermore, there are several features of MR imaging and the patient which can contribute to anxiety beyond confinement by the MR scanner. Such features may be pain, loud noise, the unknown, concerns about diagnostic findings, having to lie still, the examination duration, uncomfortable temperature or the MR scanner itself [5, 11, 45–47]. Several studies have shown that especially pain is correlated with anxiety during the scan and premature termination [11, 38, 40]. However, claustrophobia will be assessed using the CLQ , and reaching a specific score is an inclusion criterion (an arithmetic mean of greater or equal 1.0 must be reached by rating anxiety on a scale from 1 to 4 for each of 26 items). Furthermore, a custom-made questionnaire addressing prior claustrophobic events before or during scheduled MR imaging and first occurrence of claustrophobia will be fulfilled by a study assistant in the manner of a structured interview. Further questionnaires will help to examine generalized anxiety, patients' health status (including pain) and depression symptoms. The pain and noise levels which patients experience during MR imaging will be assessed directly after the scan by using horizontal visual analogue scales and patients will be asked to report whether they are afraid of diagnostic findings in MR imaging. Claustrophobia as part of e.g., a panic disorder is no exclusion criterion. However, patients will be asked to report whether they have known psychosomatic or psychiatric disorders. In general, in the majority of articles addressing anxiety leading to premature termination of MR imaging, anxiety is referred to as "claustrophobia" . For the assessment of anxiety during MR imaging it is also important to know whether patients take any anxiolytic or sedative drugs or other psychotropics which will thus be examined. Different examination times (due to different sequence duration, anxiety or complications) and different coils will also be assessed.
Another feature of MR imaging whose influence on patients' condition will be difficult to measure is the support by nursing stuff, radiographers and physicians. Several studies have shown the importance of social support and the appreciation of a caring attitude of others by anxious patients [13, 47–49]. It might yet influence patients to know that staff is aware of their anxiety and the staff may act more caring because of this awareness. However, patients' seeking social support will be assessed by evaluating coping strategies and patients will be asked to report what did particularly help them to cope with their anxiety. Furthermore, the staff will be instructed not to be "overprotective" and not to suggest coping strategies to the patients. Of course, patients will experience more attendance than in clinical routine. To keep the influence as constant as possible, patients will mainly be attended by two female staff members throughout the study and there will be a limited number of physicians and radiographers who perform MR imaging.
With regard to the comparison of image quality, the primary aim of the sequence set-up is to obtain a voxel size that is as similar as possible on both MR scanners. Thus, compromises have to be made concerning the best possible image quality still providing comparability. Motion artifacts due to anxiety might also play a role [45, 50] but should be obviated by the high number of patients and randomization.
Concerning the closed MR scanner with short- and wide-bore design which will be used in this study, it should be mentioned that there are scanners with even shorter and wider bores like the Siemens Magnetom Espree with 0,7 m diameter and 1,25 m length of the scanner bore. However, this improvement in scanner design affects the image quality which can be achieved with this MR scanner.