Interethnic variation in the prevalence of claustrophobia during MRI at Singapore General Hospital: does a wider bore MR scanner help?

Abstract

Background and objectives:

It is estimated that 60 million magnetic resonance imaging (MRI) scans are performed annually around the world. Of these, 25% of patients experienced moderate to severe claustrophobia during the procedure. The aim of this study was to determine the prevalence and interethnic variations of patients requiring sedation due to claustrophobia. Another aim was to determine if a wider bore MR scanner was helpful in reducing the incidence of claustrophobia.

Methodology:

This was an institutional review board-approved study. We retrieved records for 11,813 adult outpatients from the hospital radiological system from 1 January 2012 to 31 December 2012. The data collected included patients’ gender, age, ethnicity, body region scanned, body orientation with respect to the scanner, the types of scanners used, and the need for sedation. Statistical analysis was performed using R 3.0.1.

Results:

The prevalence of claustrophobic patients requiring sedation was 0.45%, i.e. 53. Of these, 55% were females and 45% males. Among these, 64% were Chinese, 15% Malays, 15% Indians, and 6% were other races. 74% experienced claustrophobia at the 60 cm-wide bore scanners and 26% at 70 cm-wider bore scanners. Referring to Chinese, multivariable regression showed Malays and the Indians were six times and other ethnic groups were 12 times more likely to develop claustrophobia. The incidence of claustrophobia could be reduced by a factor of 2.95 with wider bore scanners.

Conclusions:

The MR environment is still disturbing to some patients. Feet-in positioning does not significantly minimize claustrophobia. Gender and age had no bearing on claustrophobia. Wider bore MR scanners with a bore size of 70 cm are an obvious choice toward more patient-friendly MR scanners.

Keywords

Claustrophobia magnetic resonance imaging prevalence sedation interethnic variations

Introduction

It has been estimated that about 60 million magnetic resonance imaging (MRI) scans are performed every year around the world.¹ It has also been reported that 25% of patients experienced moderate to severe anxiety during the procedure. These MRI-related reactions varied from minor fear to panic attacks or claustrophobia.^2,3

Claustrophobia is defined as a strong fear of being in a small enclosed space. A patient who has claustrophobia can suffer from sweating, tachycardia, nausea, hyperventilation, and – most critically – a fear of an acute and imminent physical harm. This anxiety disorder can affect up to 15% of patients resulting in early termination or failed MRI.^2–7

The objectives of this study were twofold: firstly, it was to determine the prevalence and the interethnic variations of patients who required sedation during MRI scan due to claustrophobia. Secondly, it was to determine if a wider bore MR scanner was helpful in reducing the incidence of claustrophobia as compared to a narrow bore MR scanner.

Methods

Inclusion criteria

All outpatients aged 21 and above were included in the study. A patient would be considered claustrophobic when there was early termination of scan due to extreme anxiety, and intravenous sedation was required in order to proceed with the scan.

Exclusion criteria

All inpatients were excluded from the study.

Data acquisition

This was an institutional review board-approved retrospective study. We retrieved the subject data from our hospital radiological information system (RIS) from 1 January 2012 to 31 December 2012. There were 11,813 outpatients who had MRI scans done at our four MR scanners in Singapore General Hospital (SGH), i.e. two Siemens Avanto (1.5 T), one Siemens Verio (3 T), and one Siemens Skyra (3 T) (Siemens Medical Solutions, Erlangen, Germany). The machines were configured as indicated in Table 1.

Table 1.

Configurations of MR scanners at Singapore General Hospital.

MR scanners	Bore size (cm)	Magnet length (cm)
Siemens Skyra	70	163
Siemens Verio	70	163
Siemens Avanto	60	150

These patients were scheduled to the respective scanners by appointment staff who were unaware of this study. We recorded the ethnicity, gender, and age of the patients. We also checked the body regions scanned, the body orientation with respect to the scanner, i.e. head-in or feet-in positioning, and whether the scan was done under sedation. In cases where the scans were carried out under sedation, further checks were done on the RIS to verify the reason for sedation and the type of MR scanners used during the first attempt.

Statistical analysis

Descriptive statistical analysis was performed using R 3.0.1 (http://www.R-project.org). Univariable and multivariable regression analyses were carried out to evaluate the effects of potential factors on the onset of claustrophobia.

Results

There were 11,813 outpatients scanned at the four MR scanners during the study period. Their interethnic profile and age group distribution are summarized in Figures 1 and 2. Out of these 11,813 patients, 53 required sedation to undergo the MRI scan successfully due to claustrophobia. The overall prevalence of claustrophobia among the adult outpatients at SGH was thus 0.45% (95% confidence interval (CI): 0.34%, 0.59%).

Figure 1.

Interethnic profile of 11,813 outpatients.

Figure 2.

Age group distribution of 11,813 patients.

Of these 53 claustrophobic patients, 55% were female (29/53) and 45% were male (24/53). The age of these patients ranged from 23 to 84 years old (mean age: 51 years old). The weights of these patients ranged from 35 kg to 107 kg (mean weight: 70.5 kg) (Figure 3). In terms of ethnicity, 64% were Chinese (34/53), 15% were Malays (8/53), 15% were Indians (8/53), and 6% were of other ethnicity, i.e. one Bangladeshi and two Arabs (3/53) (Figure 4).

Figure 3.

Weight group distribution of claustrophobic patients.

Figure 4.

Interethnic variation of claustrophobic patients.

Out of all the claustrophobic patients, 74% of them (39/53) experienced claustrophobia at the two Siemens Avanto MR scanners with bore size of 60 cm. 26% of them (14/53) experienced claustrophobia at Siemens Verio and Skyra MR scanners. Both Verio and Skyra systems had a wide bore size of 70 cm (Figure 5).

Figure 5.

Bore size and claustrophobic patients.

In terms of body orientation to the scanner, 0.45% (49/10795) of claustrophobic patients were scanned with head-in positioning, i.e. brain, spine, and body scans, whereas 0.39% (4/1018) of them were scanned with feet-in positioning, i.e. knee and bony pelvis (Table 2).

Table 2.

Effects of gender, age, and body orientation on claustrophobia by means of univariable analysis.

	No. of events/no. of patients	OR (95% CI)	p-value
Gender
Female	29/5890 (0.49%)	Reference
Male	24/5923 (0.40%)	0.81 (0.47, 1.39)	0.442
Age	53/11813 (0.4%)	0.99 (0.98, 1.01)	0.257
Body orientation
Feet-in	4/1018 (0.39%)	Reference
Head-in	49/10795 (0.45%)	1.16 (0.92, 3.17)	0.104

Discussion

Our data provides the largest patient-based comparison of claustrophobia among different ethnicities, gender, age groups, and body orientations (with respect to the scanner) during MRI in Singapore. Unlike earlier reports where 80% of those affected were women,⁷ this study indicated that female patients (29/5890, 0.49%) were as claustrophobic as the male patients (24/5923, 0.40%, p = 0.442, odds ratio (OR), 0.81, 95% CI, 0.47–1.39) (Table 2). The age of the patients did not play a significant role on whether patients were likely to be claustrophobic (0.4%, p = 0.257, OR, 0.99, 95% CI, 0.98–1.01) (Table 2).

Contrary to previous studies,^8,9 it was observed here that body orientation to the scanner, i.e. head-in positioning (49/10795, 0.45%, p = 0.104, OR, 1.16, 95% CI, 0.92–3.17), did not significantly induce claustrophobia in patients. In terms of ethnicity, the Chinese (largest ethnic group in this country) were the least claustrophobic (21/9731, 0.2%). With reference to the Chinese, multivariable regression showed that both the Malays (11/736, 1.5%, p < 0.001, OR, 6.70, 95% CI, 3.10–13.70) and the Indians (11/821, 1.3%, p < 0.001, OR, 6.53, 95% CI, 3.02–13.34) were six times and the other ethnic groups were 12 times (10/525, 1.9%, p < 0.001, OR, 12.51, 95% CI, 5.50–26.72) more likely to develop claustrophobia than the Chinese (Table 3).

Table 3.

Effects of ethnicity and bore size on claustrophobia by means of multivariable regression analysis.

	No. of events/no. of patients	OR (95% CI)	p-value
Ethnicity
Chinese	21/9731 (0.2%)	Reference
Malay	11/736 (1.5%)	6.70 (3.10, 13.70)	<0.001
Indian	11/821 (1.3%)	6.53 (3.02, 13.34)	<0.001
Others	10/525 (1.9%)	12.51(5.50, 26.72)	<0.001
Bore size
70 cm	14/5351 (0.2%)	Reference
60 cm	39/6462 (0.6%)	2.95 (1.60, 5.75)	0.001

Our findings concurred with previous studies, which showed that wider bore MR scanners like our Siemens Verio and Skyra could reduce the incidence of claustrophobia.^4,9,10 In our study, the incidence could be reduced by a factor of 2.95 with the use of 70 cm-wide bore MR scanners (0.2%, 14/5351), instead of using 60 cm-wide bore MR scanners (39/6462, 0.6%, p < 0.001, OR, 2.95, 95% CI, 1.60–5.75) (Table 3).

In the West, it was reported that the patients who were claustrophobic during an MRI examination account for about 1.18–2.2% of the total.^6,11 A study using a different set of 3232 local subjects at a conventional long bore 60 cm-wide MR scanner by this author in 2007 reported a lower incidence rate of 0.8%.¹² These rates were still much higher than the current data presented here, i.e. 0.45%. One of the reasons for the lower incidence rate could be due to the introduction of wider (70 cm) bore MR scanners at SGH.

Study limitations

Our project was a single-center study with four Siemens MR scanners at SGH. The result could not be generalized to other institutions that might have different MR system configurations, e.g. General Electric or Philips MR systems. Some patients who were found to be claustrophobic at the 60 cm-wide MR scanners might be able to tolerate MRI scan successfully at a wider bore 70 cm-wide MR scanner. These subjects could be considered in future study. As claustrophobia might not be the main cause of early scan termination in adult inpatients and young children due to their underlying mental conditions, they were not included in this study.

Study implications

Since this study showed wider bore MRI scanner did reduce the incidence of claustrophobia for patients by a factor of 2.95 as compared to a narrow one, for the safety and comfort of patients and to reduce sedation rates and complications; we should reschedule all likely claustrophobic patients and also those who have failed MRI scans at the 60 cm-wide MR scanners to the 70 cm-wide bore MR scanners.

We also recommend that future acquisition of MR scanners should only be limited to the better designed patient-friendly wider bore MR scanners, i.e. bore size of at least 70 cm.

Conclusion

The MR environment is still disturbing to a small group of patients. A modification in patient positioning, i.e. feet-in first, does not significantly help in minimizing claustrophobia. Gender and age had no bearing on the incidence of claustrophobia. Although wider bore MR scanners with a bore size of at least 70 cm is an obvious choice towards a more patient-friendly MR scanners, the issue of magnetic homogeneity is still a technical challenge in producing high resolution images from these scanners. Significant interethnic variations in claustrophobia could be attributed to genetic factors,¹³ or an exposure to any environmental variables (or both) in a multi-ethnic and multi-cultural society like Singapore.

Footnotes

Acknowledgements

The authors thank Chee Kiang Lim and Tee Meng Tan, Department of Diagnostic Radiology, Singapore General Hospital, for their valuable assistance in completing this research project.

Declaration of conflicting interests

The authors declare that there are no conflicts of interest.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

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