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DOI: 10.1258/ar.2011.100396

2011 52: 570Acta Radiol Osama Al-Saeed, Mohammed Ismail, Reji Athyal and Mehraj Sheikh

Fat-saturated post gadolinium T1 imaging of the brain in multiple sclerosis

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Original article

Fat-saturated post gadolinium T1 imaging of thebrain in multiple sclerosis

Osama Al-Saeed 1, Mohammed Ismail 2, Reji Athyal 3 and Mehraj Sheikh 11 Department of Radiology, Kuwait University; 2 Ibn Sina Hospital, Kuwait; 3 Amiri Hospital, KuwaitCorrespondence to: Osama Al-Saeed. Email: [email protected]

AbstractBackground: Magnetic resonance imaging (MRI) is of vital importance in the diagnosis and follow-up of patients with multiple sclerosis (MS). Imaging sequences better demonstrating enhancing lesions can helpin detecting active MS plaques.Purpose: To evaluate the role of fat-saturated gadolinium-enhanced T1-weighted (T1W) images of the brain

in MS and to assess the benet of performing this additional sequence in the detection of enhancing lesions.Material and Methods: In a prospective study over a six-month period, 70 consecutive patients withclinically diagnosed MS were enrolled. These constituted 14 male and 56 female patients between the agesof 21 and 44 years. All the patients underwent brain MRIs on a 1.5 Tesla Magnet. Gadolinium-enhanced T1images with and without fat saturation were compared and results were recorded and analyzed using aconspicuity score and McNemar test.Results: There were a total of 157 lesions detected in 70 patients on post-contrast T1W fat-saturated imagescompared with 139 lesions seen on the post-contrast T1W fast spin-echo (FSE) images. This was because18 of the lesions (11.5%) were only seen on the fat-saturated images. In addition, 15 lesions were moreconspicuous on the fat saturation sequence (9.5%). The total conspicuity score obtained, including all thelesions, was 2.24 / 2 0.60 (SD). Using the two-tailed McNemar test for quantitative analysis, the P valueobtained was , 0.0001.Conclusion: T1W fat-saturated gadolinium-enhanced images show better lesion enhancement than T1Wimages without fat saturation.

Keywords : Multiple sclerosis, magnetic resonance imaging, fat saturation, gadolinium, brain

Submitted September 19, 2010; accepted for publication February 19, 2011

Multiple sclerosis is a chronic debilitating disease mostlikely of autoimmune etiology, involving the white matterin the central nervous system. MR imaging, especially

after intravenous administration of gadolinium chelates,helps to demonstrate the inammatory nature of thedisease and hence plays a major role in the diagnosis andfollow-up of these patients (1).

Enhancing lesions on brain MRI are more reliable in thediagnosis of MS indicating dissemination in time and spaceand are also useful in grading the severity of the disease,assessing treatment response, and documenting relapse (2).The use of the fat saturation sequence in neurologicaldisease has been limited thus far; mainly being used fordepiction of fat content in CNS tumors (35), optic neuritis(6), vertebral abnormalities (7), and in lipomatous lesionswithin the spinal canal and skull base (8). This imaging

sequence is the preferred technique on higher eld strength

magnets as against the alternative techniques of inversion recovery imaging and opposed phase imaging which are par-ticularly useful in low eld strength magnets for lesions con-

taining small amounts of fat (9). The literature on the use of fat saturation imaging sequence in MS patients is scant. Toour knowledge there is only one study on the use of fat-saturated T1-weighted sequence with intravenous gadoli-nium on a 1.0 Tesla magnet with documented benets (2).

The aim of this study was to compare fat-saturated T1Wgadolinium-enhanced images to T1W images without fatsaturation in the detection of enhancing lesions in MSpatients in 1.5T.

Material and MethodsIn a prospective six-month study, 70 consecutive patients

with clinically diagnosed MS were enrolled. These

Acta Radiologica 2011; 52 : 570574. DOI: 10.1258 / ar.2011.100396

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constituted 14 male and 56 female patients between the agesof 21 and 44 years. The imaging session in all the patientswas part of the regular follow-up of cases diagnosed with MS. The study was approved by university ethics commit-tee, and patient consent was obtained for additionalsequences.

All the patients underwent brain MRIs on a 1.5 Tesla

machine (GE Signa 1.5T Echospeed, GE Healthcare,Milwaukee, WI, USA) using an 8-channel head coil. Thepre-contrast imaging included the axial T1W FSE, axialT2W FSE, T2W Flair, and sagittal Flair sequences.

Three minutes after IV contrast by a manual injection of 0.1 mmol / kg body weight of gadodiamide (Omniscan, GEHealth care, Cork, Ireland) over 30 s, axial T1W FSE andaxial T1W fat-saturated sequences were performed. TheT1W FSE sequence (TR 600, TE min, Echotrain 2, FOV 24,NEX 2, Freq 384, phase 256, thickness 5) took an averageof 2 min and 30 s to perform and the T1W fat-saturatedsequence (TR 600, TE min, Echotrain 2, FOV 24, NEX 2,Freq 384, phase 256, thickness 5) took an average of 5 min

and 12 s.These two sequences were alternatively performed rst toavoid bias related to timing of the scans.

The resultant sequences were analyzed by two experi-enced MR radiologists (OS and MI) each with over 15years of experience in MR imaging. The analysis was per-formed on a consensual basis. Using a full screen, 21-inch monitor with 2K resolution (Barco, Mfgd 3420, Brussels,Belgium), enhancing lesions were counted one image at atime on both T1W FSE images and T1W fat-saturatedimages. A simultaneous comparison between the twosequences was performed. The two radiologists assigned aconspicuity score for each enhancing lesion on both T1W

sequences by direct visual comparison between the two cor-responding images. A scoring system was used wherein thehighest score of three was assigned if the lesion was only

seen or better visualized on T1W fat-saturated imagescompared to T1W FSE images, the lowest score of onewas assigned if the lesion was relatively more difcult tosee or not seen on T1W fat-saturated images compared toT1W FSE, and a score of 2 was assigned if the lesion wasequally well-seen on both sequences. Statistical analysis of the ndings was performed using McNemar test for

quantitative evaluation of the number of lesions.

ResultsThere were a total of 1069 lesions seen on T2W and Flairimages. Out of those, 139 lesions were seen on the post-contrast T1W FSE images in the 70 patients; whereas on post-contrast T1W fat-saturated sequences, 157 lesionswere detected, indicating that 18 additional lesions (11.5%)were only seen on the fat-saturated images (Figs. 1 and 2)(Table 1). Additionally there were 15 lesions (9.5 %) thatwere better seen on the fat saturation sequence (Fig. 3)(Table 2). All the lesions detected on either of the two

T1W sequences (157 in total) including the 18 only seen on T1W fat-saturated sequences were evident as hyper-intense foci on T2W and Flair images. In scoring the 157lesions detected, 18 of the lesions were only detected on fat-saturated images (score 3). Four lesions were better seen on T1W FSE images (score 1), and 15 better seen on fat-saturated images (score 3). The remaining 120 lesions wereequally well-seen on both the sequences (score 2). By statisti-cal analysis the conspicuity score obtained for all the lesionswas 2.24 / 2 0.60 (SD) with P value , 0.0001 by the two-tailed McNemar test.

In all the patients where a lesion was better seen in one of the two post-contrast sequences (four on T1W FSE and 15

on fat saturated), it was noted that this particular sequencewas performed second. Likewise, the 18 lesions detected on fat-saturated images were all seen in patients in whom the

Fig. 1 29-year-old woman with recently diagnosed multiple sclerosis. (a) Axial T1WI demonstrates no denite enhancement. (b) However, the lesion is well visu-

alized on the fat saturation scan adjacent to the posterior part of the left lateral ventricle

Fat-saturated post gadolinium T1 imaging of the brain in multiple sclerosis 571. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .



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fat-saturated sequence was performed after the T1W FSEsequence.

DiscussionIn this study, there were 18 (11.5%) lesions of a total of 157enhancing lesions that were only seen on gadolinium-enhanced fat-saturated T1W images, and 15 (9.5%)

additional lesions were better seen on the fat-saturatedimages compared with regular post-contrast T1W images.The contribution of MR imaging in the diagnosis of MS is

well established. The ndings detected on cranial MRI in aclinically suspected case constitute part of the algorithm forinitial diagnosis and follow-up (10). Enhancing white matterfoci that are indicative of inammatory activity of demyeli-nating lesions alter the grade and stage of disease (1). Theyare considered to reect the disruption of the bloodbrain barrier with a consequent shortening of T1 relaxation timeand hyperintensity on the T1-weighted sequence obtainedafter administration of gadolinium chelates (2, 11). Anytechnique wherein enhancing lesions are better demon-

strated would hence play an important contributory rolein the diagnosis and in grading the severity of the disease.There are several techniques that have been studied to

improve the visualization of enhancing plaques in multiplesclerosis. These include triple-dose administration of gadoli-nium (1216), thin (3 mm) post-contrast sections withoutspacing (17), magnetization transfer (1821) and delayedpost-contrast imaging (22, 23). Triple-dose contrast adminis-tration and the alternate improved technique of three sub-sequent single doses have been reported to pick up manymore lesions but are expensive and may possibly showenhancement that might not be clinically signicant (24).Furthermore, post-contrast non-spaced sections are time

consuming. Magnetization transfer images suffer from

pseudo-enhancement (25 27) and would require pre-contrast MT images to be performed which signicantlyincreases the time for scanning. Delaying acquisition of images after contrast injection is reported to signicantlyincrease the visualization of images (22) and could beachieved by performing T2W and air imaging between contrast injection and post-contrast T1W scans. A recentmulticenter study in 113 patients (28) with brain lesions con-

cluded that MR imaging with Gadobenate dimeglumineprovides signicantly greater diagnostic information andbetter lesion enhancement compared to Gadodiamide atan equivalent dose.

Fat saturation has been attempted before using a 1Tmagnet and imaging after contrast. Fat saturation is the pre-ferred means of fat suppression when using higher eldmagnets (9). The increased detection and conspicuity of lesions on fat-saturated post-contrast images has been attrib-uted to the reduction in signal from lipids in the relativelyintact myelin, a MT effect, and the improved overall imagecontrast due to signal loss of subcutaneous and marrowfat (2).

We found signicantly improved detection of lesions in the fat-saturated post-contrast T1W image (33 or 21% of all enhancing lesions are either only seen or more conspicu-ous) compared with regular post-contrast images. Therewere 18 lesions that were not identiable on the regularpost-contrast images but were seen only on the fat-saturatedimages. Although our gure (21%) with the 1.5 T scanner islower, our ndings are in agreement with the resultsobtained by Sardanelli et al. (2) who reported a 30% increasein the number of lesions on fat-saturated images andimproved conspicuity on a 1T MRI magnet.

In our study we scheduled the sequences so that each of the two post-contrast sequences were alternately performed

rst in our subjects to avoid the potential bias due to the

Fig. 2 39-year-old man with known multiple sclerosis for follow-up scan. (a) Gadolinium-enhanced axial T1WI shows no abnormal enhancement. (b) Fat satur-ation scan reveals clear focal left inferior cerebellar enhancement

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variable timing of imaging after contrast injection. Therewas no signicant difference noted in regards to the orderof performing the two sequences in the 120 lesions thatwere equally well seen. However, all the 37 lesions betteror only seen on any one of the two sequences (33 better oronly seen on fat-saturated images and four better seen on T1W FSE images) were detected on images where therespective sequence was performed second. It should bementioned that when performed second, the fat-saturatedsequence was performed at approximately 5 min and 30 safter contrast (3 min plus 2 min and 30 s for the rst post-contrast sequence) and the T1W FSE was performed atapproximately 8 min and 12 s after contrast (3 min plus5 min and 12 s for the rst post-contrast sequence). Theimproved detection cannot thus be attributed only to thedelayed time of scanning, for then there should have been many more lesions detected on T1W FSE considering thatthis sequence was performed even later when donesecond. The delay in scanning does however help and aminimum delay of 5 min after IV contrast as recommendedin the current imaging guidelines should be adequate tomaximize lesion detection.

These ndings correlate with the previously reportednding (22) of better visualization on more delayedimaging. The consortium of MS centers consensus guide-lines on MR imaging in multiple sclerosis has also taken note of the fact that delayed imaging does increase lesion conspicuity and number. For this reason they have rec-ommended that the gadolinium-enhanced axial T1W scansbe taken 5 min after contrast administration (29).

The use of 1.5T magnet in our study is also important asfat saturation is better on higher eld strength as a conse-quence of decreased artifacts related to magnetic eld in homogeneities when the strength of the magnet is increasedwhile keeping other parameters constant (30). The time forimaging is increased; in our case it was increased from2 min and 30 s to 5 min and 12 s, which, although signi-cant, would be less than other approaches like MTimaging and delayed post-contrast scanning.

A limitation of the study was that an even more delayedpost-contrast scanning was not utilized. We sought toensure that the second performed post-contrast sequencewas taken at least 5 min after IV contrast according to theguidelines of the consortium of MS centers (29). However,several centers currently perform the T2W and airimaging sequence between the contrast injection and post-contrast T1W scans thereby further delaying the time of scanning to approximately 9 10 minutes. This wouldpotentially have increased the yield of enhancing lesionsin our study while permitting the total examination timeto remain constant.

In conclusion, our study revealed that the use of gadolinium-enhanced fat saturation T1W sequence in patients scanned at least 5 min after contrast administration improved the detection and conspicuity of the lesions in patients with MS. T1W fat-saturated post-contrast imagingcould constitute an alternative sequence and replace the

Fig. 3 38-year-old woman with remitting-relapsing multiple sclerosis. (a) Gadolinium-enhanced axial T1WI shows very faint small focal enhancement in the right

occipital lobe. (b) The lesion is more conspicuous on the gadolinium-enhanced fat-saturated T1WI

Table 2. Conspicuity of lesions on T1W sequences (total number 157)

Lesion betterseen on T1WFSE than T1WFS

Lesion visualizationsame on TW1 FSE as onT1W FS (score 2)

Lesion better (or only)seen on T1W FS thanT1W FSE sequence(score 3)

4 120 33 (15 18)

T1W FSE

T1-weighted fast spin-echo, T1W FS

T1-weightedfat-saturated sequence

Table 1. Enhancing lesions seen on T1W sequences

Seen on both T1W FSEand T1W FS

Seen only on T1W FS

Seen only on T1W FSE

139 18 0

T1W FSE T1-weighted fast spin-echo, T1W FS T1-weighted fat-saturated sequence

Fat-saturated post gadolinium T1 imaging of the brain in multiple sclerosis 573. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .



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regular post-contrast T1W imaging for better demonstration of lesions and hence could play an important role in theinitial diagnosis and follow-up in patients with MS.

Conict of interest: None.

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