# Abstract

 

## Background The purpose of the present study was to compare the image quality of spinal magnetic resonance (MR) imaging performed on a high-field horizontal open versus a short-bore MR scanner in a randomized controlled study setup. 

## Methods Altogether, 93 (80% women, mean age 53) consecutive patients underwent spine imaging after random assignement to a 1-T horizontal open MR scanner with a vertical magnetic field or a 1.5-T short-bore MR scanner. This patient subset was part of a larger cohort. Image quality was assessed by determining qualitative parameters, signal-to-noise (SNR) and contrast-to-noise ratios (CNR), and quantitative contour sharpness. 

## Results The image quality parameters were higher for short-bore MR imaging. Regarding all sequences, the relative differences were 39% for the mean overall qualitative image quality, 53% for the mean SNR values, and 34--37% for the quantitative contour sharpness (*P*\<0.0001). The CNR values were also higher for images obtained with the short-bore MR scanner. No sequence was of very poor (nondiagnostic) image quality. Scanning times were significantly longer for examinations performed on the open MR scanner (mean: 32±22 min versus 20±9 min; *P*\<0.0001). 

## Conclusions In this randomized controlled comparison of spinal MR imaging with an open versus a short-bore scanner, short-bore MR imaging revealed considerably higher image quality with shorter scanning times. 

## Trial Registration ClinicalTrials.gov [NCT00715806](#) # Results 

## Participants Of 174 enrolled patients, 106 had a clinical indication for MR imaging of the spine: 35 cervicothoracic spine, 61 thoracolumbar spine, 10 whole spine. Of these 106 patients, 93 underwent MR imaging, and all were included in this analysis ([Figure 1](#)). [Table 1](#) lists the baseline characteristics of the patients included. They were well matched between both groups. Eighty percent of the patients were women who have been shown to be more likely to suffer from claustrophobia [[8]](#). The mean age was 53 (SD, 12; range, 27-88), and the mean body mass index (BMI) was 29 (SD, 7.5; range, 17.5--52). All patients were at increased risk to suffer from claustrophobia. The mean CLQ score was 2,35 (SD, 0.69) which is in accordance with other high-risk groups [[16]](#). Moreover, 50.5% of the 93 patients had prior MR imaging which was prevented, aborted or performed with sedation due to claustrophobia. Indications for MR imaging included: radicular pain (n = 60), (non-motor) neurologic symptoms and/or deficits (n = 60), motor deficits (n = 28), history of prior surgery (n = 10), cauda equina syndrome (n = 4), suspicion of cancer (n = 3), and history of previous trauma (n = 2). Some patients had more than one clinical indication for MR imaging. All indications were appropriate according to American College of Radiology guidelines [[8]](#), [[19]](#), [[20]](#). ::::table-wrap

10.1371/journal.pone.0083427.t001

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##

##

## Characteristics of the 93 Randomized Patients who Underwent Spinal MR Imaging.

:::

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```
                                              Short-Bore MR (n = 44)   Open MR (n = 49)   *P* Value
```

______________________________________________________________________

Female sex 35 (79.5) 40 (81.6) .8
Age 53 (SD, 11.4) 53.1 (SD, 12.7) .1
Age categories .7
\<30 0 (0) 1 (2)\
30 - \<50 22 (50) 23 (46.9)\
50 - \<70 16 (36.4) 20 (40.8)\
≥70 6 (13.6) 5 (10.2)\
Body height in cm 167.9 (SD, 8.6) 168.3 (SD, 10.3) .8
Body weight in kg 79.6 (SD, 23.3) 84.9 (SD, 25.9) .3
Body mass index (BMI) 28.1 (SD, 7.7) 29.7 (SD, 7.3) .3
BMI categories .5
\<20 4 (9.1) 1 (2)\
20- \<3 (54.5) 28 (57.1)\
30- \<40 12 (27.3) 15 (30.6)\
≥40 4 (9.1) 5 (10.2)\
Maximum body circumference in cm 112.8 (SD, 17.3) 115.6 (SD, 14.4) .4
Region of MR imaging .9
Cervicothoracic spine 14 (31.8) 15 (30.6)\
Thoracolumbar spine 26 (59.1) 28 (57.1)\
Whole spine 4 (9.1) 6 (12.2)\
Claustrophobia Questionnaire mean value[a](#) 2.38 (SD, 0.75) 2.32 (SD, 0.65) .7
State anxiety before MR imaging[b](#) 2.65 (SD, 0.56) 2.65 (SD, 0.68) 1

Data are number (%) or arithmetic mean (SD). Percentages may not total
100% because of rounding.

^a^ The Claustrophobia Questionnaire (CLQ) [[16]](#) consists of 26
items which assess two separate but related fears hypothesized to
comprise claustrophobia: the fear of suffocation and the fear of
restriction. For each of the 26 items of the CLQ, anxiety is rated on a
scale from 0 (not at all anxious) to 4 (extremely anxious).

^b^ Directly before MR imaging, the State questionnaire of the
Spielberger State-Trait Anxiety Inventory (STAI) [[33]](#) was used to
assess patients' state anxiety. It consits of 20 items to be rated on a
scale from 1 (almost never) to 4 (very much so).:::: 

## MR Imaging In the 93 patients who underwent spinal MR imaging there were 48 examinations on the short-bore MR scanner and 55 examinations on the open MR scanner. 25 examinations were performed after cross-referral, 16 of them with conscious sedation ([Figure 1](#), [Table 2](#)). Only one patient aborted MR imaging on the first scanner due to claustrophobia after one sequence, which was thus not included in the primary analysis. The other patients who were imaged after cross-referral rejected MR imaging on the first scanner before the examination had started ([Figure 1](#)). Thus, none of the patients was scanned on both scanners. Details of the MR imaging characteristics are listed in [Table 2](#). Scanning times were significantly longer for open MR imaging and the perceived noise and pain levels were also higher, although statistically not significant, in patients who were examined with the open MR scanner [[8]](#). ::::table-wrap
10.1371/journal.pone.0083427.t002

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##

##

## Characteristics of the MR Examinations.

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```
                                Short-Bore MR Group   Open MR           *P* Value
```

______________________________________________________________________

Number of MR examinations[a](#) 48 55 .9
Cervicothoracic spine 18 (37.5) 21 (38.2)\
Thoracolumbar spine 30 (62.5) 34 (61.8)\
Number of MR sequences\
T1w/T2w sagittal 48 55 .9
Cervicothoracic spine 18 (37.5) 21 (38.2)\
Thoracolumbar spine 30 (62.5) 34 (61.8)\
T2w axial[b](#) 68 76 .9
Cervicothoracic spine 19 (28) 22 (28.9)\
Thoracolumbar spine 49 (72) 54 (71.1)\
Scan duration (min) 19.8 (SD, 8.5) 31.7 (SD, 21.6) .001
Cervicothoracic spine 19 (SD, 5.3) 30.1 (SD, 7.8) .001
Thoracolumbar spine 17.5 (SD, 7.1) 25.8 (SD, 10.2) .001
Whole spine 37 (SD, 6.8) 70 (SD, 42) .2
Anxiety[c](#) 58.1 (SD, 33.9) 50.3 (SD, 30.6) .3
Cervicothoracic spine 58.6 (SD, 34.9) 48.1 (SD, 30.1) .4
Thoracolumbar spine 55.8 (SD, 32.8) 51.8 (SD, 31.9) .7
Whole spine 71 (SD, 44.8) 49 (SD, 30.5) .4
Noise[c](#) 57.5 (SD, 21.3) 65.9 (SD, 23.1) .08
Cervicothoracic spine 52.2 (SD, 24) 62.5 (SD, 25) .3
Thoracolumbar spine 58.5 (SD, 18.3) 71.6 (SD, 21.1) .02
Whole spine 69.8 (SD, 29.2) 47.7 (SD, 18.6) .2
Pain[c](#) 19.8 (SD, 27.5) 31 (SD, 32.5) .08
Cervicothoracic spine 20 (SD, 29.7) 27.6 (SD, 28.7) .5
Thoracolumbar spine 21.2 (SD, 28.3) 28.6 (SD, 33.8) .4
Whole spine 10.5 (SD, 15.8) 51.2 (SD, 33.7) .06

Data are number (%) or arithmetic mean (SD). Percentages may not total
100% because of rounding.

^a^ For the analysis, MR imaging of the whole spine was categorized as
imaging of the cervicothoracic and the thoracolumbar spine.

^b^ The number of axial sequences and the segment of the vertebral
column that was imaged with axial sequences were chosen according to the
medical indication.

^c^ The pain, noise, and anxiety levels patients experienced during MR
imaging were assessed directly after the scan using horizontal and
nonmarked (0--100 mm) visual analogue scales.:::: Results of all examinations were of diagnostic image quality. The main findings included: disc protrusion (n = 58), disc extrusion (n = 44), degenerative spondylarthrosis (n = 45), neural foraminal narrowing (n = 42), nerve root compression/irritation (n = 35), spinal stenosis (n = 33), intervertebral osteochondrosis (n = 28), myelopathy/spinal cord lesions (n = 5), fracture (n = 4), metastasis (n = 2), spondylolisthesis (n = 2), and spondylodiscitis (n = 1). 

## Qualitative Analysis Qualitative overall image quality of all available imaging sequences, assessed by two blinded examiners in consensus, was rated significantly higher for short-bore MR images than for open MR images (1.92 [SD, 0.74] versus 3.16 [SD, 0.77]; *P*\<0.0001). No sequence was rated very poor (nondiagnostic). Thus image quality scores ranged from 1 (optimal) to 4 (poor). [Table 3](#) shows the respective results computed separately for all qualitative parameters which were assessed. There were significantly more artifacts in sagittal T1-weighted sequences of the cervicothoracic and the thoracolumbar spine and in axial T2-weighted sequences of the thoracolumbar spine when obtained with the open MR scanner. Relevant artifacts were mainly due to motion for both, short-bore and open MR imaging. However, none of the examinations showed severe artifacts limiting their diagnostic value. Subgroup analyses excluding patients who underwent imaging after cross-referral revealed equally distributed results (*P*\<0.0001, data not shown). Analysis of only those examinations which were performed with sedation also revealed higher qualitative image quality ratings for short-bore MR, but significant differences were only found for axial sequences (data not shown). [Figures 2](#) to [5](#) show examples of MR images representing the respective range of qualitative image quality for the two scanners. <figure> 10.1371/journal.pone.0083427.g002 <p><img src="" /></p> <figcaption>Representative Examples of Image Quality on Sagittal T1- and T2-Weighted Sequences of the Cervical Spine.<br /> Top row: sagittal T1-weighted turbo spin-echo sequences of the cervicothoracic spine of four patients, representing the range of qualitative image quality scores obtained with short-bore (A, C) and open MR imaging (B, D). Overall image quality ratings were: “optimal” for sequence A,“good” for B, “moderate” for C, and “poor” for D. No sequence was rated very poor (nondiagnostic). Bottom row: sagittal T2-weighted turbo spin-echo sequences of the cervicothoracic spine of the same four patients obtained with short-bore (E, G) and open MR imaging (F, H). Overall image quality ratings were: “good” for sequence E,“good” for F, “moderate” for G, and “good” for H. No sequence was rated very poor (nondiagnostic).</figcaption> </figure> <figure> 10.1371/journal.pone.0083427.g003 <p><img src="" /></p> <figcaption>Representative Examples of Image Quality on Sagittal T2- and T1-Weighted Sequences of the Lumbar Spine.<br /> Top row: sagittal T2-weighted turbo spin-echo sequences of the lumbar spine of four patients, representing the range of qualitative image quality scores obtained with short-bore (A, C) and open MR imaging (B, D). Overall image quality ratings were: “optimal” for A,“good” for B, “moderate” for C, and “poor” for D. No sequence was rated very poor (nondiagnostic). Bottom row: sagittal T1-weighted turbo spin-echo sequences of the lumbar spine of the same four patients obtained with short-bore (E, G) and open MR imaging (F, H). Overall image quality ratings were: “good” for sequence E,“moderate” for F, “good” for G, and “poor” for H. No sequence was rated very poor (nondiagnostic).</figcaption> </figure> <figure> 10.1371/journal.pone.0083427.g004 <p><img src="" /></p> <figcaption>Representative Examples of Image Quality on Axial T2-Weighted Sequences of the Cervical Spine.<br /> Axial T2-weighted medic sequences of the cervical spine of four patients, representing the range of qualitative image quality scores obtained with short-bore (A, B) and open MR imaging (C, D). Overall image quality ratings were: “optimal” for sequence A,“good” for sequence B, “moderate” for C, and “poor” for D. No sequence was rated very poor (nondiagnostic).</figcaption> </figure> <figure> 10.1371/journal.pone.0083427.g005 <p><img src="" /></p> <figcaption>Representative Examples of Image Quality on Axial T2-weighted Sequences of the Thoracolumbar Spine.<br /> Axial T2-weighted sequences of the lumbar spine of four patients, representing the range of qualitative image quality scores obtained with short-bore (A, C) and open MR imaging (B, D). Overall image quality ratings were: “optimal” for sequence A,“good” for sequence B, “moderate” for C, and “poor” for D. No sequence was rated very poor (nondiagnostic).</figcaption> </figure> ::::table-wrap
10.1371/journal.pone.0083427.t003

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##

##

## Qualitative Image Quality Parameters.

:::

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```
                      Cervicothoracic Spine                     Thoracolumbar Spine                                              
```

______________________________________________________________________

```
                      Short-Bore MR Imaging   Open MR Imaging   *P* Value              Short-Bore MR Imaging   Open MR Imaging   *P* Value
                      Arithmetic mean (SD)                      Arithmetic mean (SD)                                             
```

**T2w sagittal** n = 18 n = 21 n = 30 n = 34\
Overall image quality 2.1 (1.1) 3 (1) .006 1.8 (0.7) 2.7 (0.7) \<.0001
Contrast 1.8 (0.9) 2.8 (0.8) .003 1.7 (0.7) 2.4 (0.7) \<.0001
Contour sharpness 2.2 (1) 2.9 (0.9) .03 1.7 (0.7) 2.2 (0.6) .002
Noise 1.7 (0.6) 32 (0.8) \<.0001 2.2 (0.6) 3.2 (0.7) \<.0001
Artifacts[a](#) 2.6 (1) 2.2 (0.9) .25 2.1 (0.7) 2.3 (0.6) .11
**T1w sagittal** n = 18 n = 21 n = 30 n = 34\
Overall image quality 1.8 (0.8) 3.5 (0.7) \<.0001 1.8 (0.6) 2.7 (0.6) \<.0001
Contrast 1.9 (0.8) 3.2 (0.7) \<.0001 2 (0.7) 2.7 (0.6) \<.0001
Contour sharpness 2.2 (0.9) 3.8 (0.5) \<.0001 1.9 (0.6) 2.7 (0.6) \<.0001
Noise 1.6 (0.6) 2.7 (1) .001 1.6 (0.5) 2.5 (0.6) \<.0001
Artifacts[a](#) 1.7 (0.8) 3 (1) \<.0001 1.6 (0.7) 2.6 (0.7) \<.0001
**T2w axial** n = 19 n = 22 n  = 49 n = 54\
Overall image quality 2.1 (0.7) 3.4 (0.7) \<.0001 2 (0.7) 3.5 (0.6) \<.0001
Contrast 2.2 (0.7) 3.2 (0.7) \<.0001 2.1 (0.8) 3.3 (0.6) \<.0001
Contour sharpness 2.1 (0.7) 3.2 (0.7) \<.0001 1.8 (0.7) 3 (0.6) \<.0001
Noise 1.8 (0.5) 3.5 (0.6) \<.0001 2.2 (0.6) 3.9 (0.4) \<.0001
Artifacts 2.7 (0.6) 2.7 (1) .9 2.1 (0.9) 3.1 (0.8) \<.0001

An optimal score is defined as 1 and a poor score as 4. No sequence was
rated nondiagnostic (score of 5) for any qualitative parameter.

^a^ Artifacts were mainly due to motion for both, short-bore and open MR
imaging.:::: 

## Quantitative Analysis Quantitative image quality parameters were in good agreement with the qualitative image quality results. The results computed separately for the different sequences of the cervicothoracic and the thoracolumbar spine are listed in [Table 4](#). SNR was assessed for corticospinal fluid, spinal cord, vertebral bone, fat tissue, and muscle and an overall mean value was calculated. The mean SNR values of all available sequences were significantly higher for short-bore MR images than for open MR images (17.97 [SD, 6.58] versus 11.28 [SD, 4.35]; *P*\<0.0001). The CNR values calculated were also higher for images obtained with the short-bore MR scanner ([Table 4](#)). Regarding quantitative assessment of contour sharpness, the mean values for the two assessed interfaces were significantly smaller in MR images obtained with the short-bore scanner than with the open MR scanner, thus indicating an improved contour sharpness (0.95 [SD, 0.24] versus 1.43 [SD, 0.48] and 0.83 [SD, 0.22] versus 1.32 [SD, 0.51]; *P*\<0.0001). The detailed results of the contour sharpness measurement are also shown in [Figures 6](#) and [7](#). Subgroup analyses of patients who underwent MR imaging without cross-referral and of sedated patients revealed similar results (data not shown). <figure> 10.1371/journal.pone.0083427.g006 <p><img src="" /></p> <figcaption>Contour Sharpness in MR images of the Cervicothoracic Spine.<br /> Contour sharpness as distance in mm (±SD) that is neeeded for the signal to increase from 25% to 75% of the grayscale pixel value profile obtained with imageJ (see <a href="#">Figure S1</a>). Contour sharpness was defined for the interface between corticospinal fluid (CSF) and spinal cord (SC), and between corticospinal fluid and vertebral body (B)/posterior longitudinal ligament (L) in sagittal T2-weighted, sagittal T1-weighted and axial T2-weighted sequences. <em>P</em> values were \<0.0001 for all assessed contours.</figcaption> </figure> <figure> 10.1371/journal.pone.0083427.g007 <p><img src="" /></p> <figcaption>Contour sharpness in MR images of the thoracolumbar spine.<br /> Contour sharpness as distance in mm (±SD) that is neeeded for the signal to increase from 25% to 75% of the grayscale pixel value profile obtained with imageJ (see <a href="#">Figure S1</a>). Contour sharpness was defined for the interface between corticospinal fluid (CSF) and spinal cord (SC), and between corticospinal fluid and vertebral body (B)/posterior longitudinal ligament (L) in sagittal T2-weighted, sagittal T1-weighted and axial T2-weighted sequences. In axial MR imaging of the thoracolumbar spine the spinal cord was normally not included and could thus not be assessed. <em>P</em> values were \<0.0001 for all assessed contours.</figcaption> </figure> ::::table-wrap
10.1371/journal.pone.0083427.t004

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##

##

## Quantitative Image Quality Parameters.

:::

![](<>)

```
                                               Cervicothoracic Spine                     Thoracolumbar Spine                                              
```

______________________________________________________________________

```
                                               Short-Bore MR Imaging   Open MR Imaging   *P* Value              Short-Bore MR Imaging   Open MR Imaging   *P* Value
                                               Arithmetic mean (SD)                      Arithmetic mean (SD)                                             
```

**T2w sagittal** n = 18 n = 21 n = 30 n = 34\
SNR[a](#) 16.9 (3.4) 9.23 (2.1) \<.0001 16.4 (3.7) 11.7 (2.8) \<.0001
CNR[b](#)\
Cerebrospinal fluid -- Spinal cord 18.1 (11.6) 9.3 (5.5) .005 22.3 (13.2) 14 (5.6) .007
Cerebrospinal fluid -- Vertebral bone 19.3 (10.3) 8.2 (5.7) \<.0001 24 (12.9) 11.7 (6.3) \<.0001
Contour sharpness[c](#)\
Cerebrospinal fluid -- Spinal cord 0.8 (0.1) 1.1 (0.2) \<.0001 0.9 (0.1) 1.5 (0.4) \<.0001
Cerebrospinal fluid -- Vertebral bone 0.8 (0.1) 1.1 (0.2) \<.0001 0.8 (0.1) 1.2 (0.4) \<.0001
**T1w sagittal** n = 18 n = 22 n = 30 n = 34\
SNR[a](#) 22.9 (5.6) 14.4 (3.6) \<.0001 21.6 (4.4) 16.2 (3.4) \<.0001
CNR[b](#)\
Cerebrospinal fluid -- Spinal cord 10.3 (11.5) 8.9 (5.1) .6 17.7 (14.8) 9.4 (7) .008
Cerebrospinal fluid -- Vertebral bone 8.4 (6.1) 5.7 (3.8) .1 8.2 (8.1) 3.9 (2.6) .009
Contour sharpness[c](#)\
Cerebrospinal fluid -- Spinal cord 1.1 (0.1) 1.7 (0.4) \<.0001 1.2 (0.3) 1.8 (0.4) \<.0001
Cerebrospinal fluid -- Vertebral bone 1.1 (0.1) 1.9 (0.5) \<.0001 1.1 (0.1) 1.8 (0.4) \<.0001
**T2w axial**[d](#) n = 19 n = 22 n  = 49 n = 54\
SNR[a](#) 23.1 (6.4) 11.9 (2.7) \<.0001 13.2 (6.6) 7.3 (2.6) \<.0001
CNR[b](#)\
Cerebrospinal fluid -- Spinal cord 11.9 (13.3) 11.1 (8.6) .8\
White matter -- Gray matter of the spinal cord 10.9 (12.7) 7.2 (4.7) .2\
Cerebrospinal fluid -- Vertebral bone 23.1 (14.2) 17.2 (10.9) .1 15.2 (27.8) 8.9 (4.9) .1
Contour sharpness[c](#)\
Cerebrospinal fluid -- Spinal cord 0.7 (0.1) 0.9 (0.2) \<.0001\
Cerebrospinal fluid -- Vertebral bone 0.8 (0.1) 1.3 (0.4) \<.0001 0.6 (0.1) 1(0.3) \<.0001

^a^ Overall mean value of signal-to-noise ratios (SNR) for corticospinal
fluid, spinal cord, vertebral bone, fat tissue, and muscle.

^b^ Contrast-to-noise ratios (CNR) were calculated by substracting the
respective SNR.

^c^ Values are distances in mm (±SD) that are neeeded for the signal to
increase from 25% to 75% of the grayscale pixel value profile obtained
with imageJ.

^d^ In axial MR imaging of the thoracolumbar spine, the spinal cord was
normally not included and could thus not be assessed.::::


Extracted trial result:
Outcome: quantitative contour sharpness of the Cervicothoracic Spine (continuous)
Intervention: short-bore MR scanner
Comparator: high-field horizontal open MR scanner
Intervention group size: 18
Intervention mean: 0.95
Intervention standard deviation: 0.24
Comparator group size: 21
Comparator mean: 1.43
Comparator standard deviation: 0.48
Notes: Original outcome was "quantitative contour sharpness".