Koutsiaris 2013_b_ΜRI BLADE_Lumbar Spine

Magnetic Resonance Imaging xxx (2013) xxx–xxx

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Magnetic Resonance Imaging

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Elimination of motion, pulsatile flow and cross-talk artifacts using blade sequencesin lumbar spine MR imaging

Eleftherios Lavdas a, Panayiotis Mavroidis b,c,⁎, Spiros Kostopoulos d, Dimitrios Glotsos d, Violeta Roka e,Aristotle G. Koutsiaris f, Georgios Batsikas g, Georgios K. Sakkas h, Antonios Tsagkalis i, Ioannis Notaras i,Sotirios Stathakis b, Nikos Papanikolaou b, Katerina Vassiou j

a Department of Medical Radiological Technologists, Technological Education Institute of Athens, Greeceb Department of Radiological Sciences, University of Texas Health Sciences Center at San Antonio, San Antonio, TX, USAc Department of Medical Radiation Physics, Karolinska Institutet & Stockholm University, Stockholm, Swedend Department of Medical Instruments Technology, Technological Education Institute of Athens, Greecee Health Center of Farkadona, Trikala, Greecef Bioinformatics Laboratory, Department of Medical Laboratories, School of Health Sciences, Technological Educational Institute of Larissa, Larissa, Greeceg Department of Medical Imaging, IASO Thessalias Hospital, Larissa, Greeceh Center for Research and Technology Thessaly Trikalai Department of Orthopaedic Surgery, IASO Thessalias Hospital, Larissa, Greecej Department of Radiology, Medical School, University of Thessaly, Larissa, Greece

a b s t r a c ta r t i c l e i n f o

⁎ Corresponding author. Division of Medical Physics, DSciences, Cancer Therapy and Research Center, UniversCenter San Antonio, MC 7889, San Antonio TX 78229–41027; fax: +1 210 478 9703.

E-mail address: [email protected] (P. Mavroidi

0730-725X/$ – see front matter © 2013 Elsevier Inc. Alhttp://dx.doi.org/10.1016/j.mri.2013.03.006

Please cite this article as: Lavdas E, et al, Espine MR imaging, Magn Reson Imaging (2

Article history:Received 24 October 2012Revised 28 January 2013Accepted 8 March 2013Available online xxxx

Keywords:1.5 T MRIMotionPulsatile flow and cross-talk artifactsBLADE sequencesLumbar spine examination

The purpose of this study is to evaluate the ability of T2 turbo spin echo (TSE) axial and sagittal BLADEsequences in reducing or even eliminating motion, pulsatile flow and cross-talk artifacts in lumbar spineMRI examinations. Forty four patients, who had routinely undergone a lumbar spine examination,participated in the study. The following pairs of sequences with and without BLADE were compared: a) T2TSE Sagittal (SAG) in thirty two cases, and b) T2 TSE Axial (AX) also in thirty two cases. Both quantitativeand qualitative analyses were performed based on measurements in different normal anatomicalstructures and examination of seven characteristics, respectively. The qualitative analysis was performedby experienced radiologists. Also, the presence of image motion, pulsatile flow and cross-talk artifacts wasevaluated. Based on the results of the qualitative analysis for the different sequences and anatomicalstructures, the BLADE sequences were found to be significantly superior to the conventional ones in all thecases. The BLADE sequences eliminated the motion artifacts in all the cases. In our results, it was found thatin the examined sequences (sagittal and axial) the differences between the BLADE and conventionalsequences regarding the elimination of motion, pulsatile flow and cross-talk artifacts were statisticallysignificant. In all the comparisons, the T2 TSE BLADE sequences were significantly superior to thecorresponding conventional sequences regarding the classification of their image quality. In conclusion,this technique appears to be capable of potentially eliminating motion, pulsatile flow and cross-talkartifacts in lumbar spine MR images and producing high quality images in collaborative and non-collaborative patients.

epartment of Radiologicality of Texas Health Science427, USA. Tel.: +1 210 450

s).

l rights reserved.

limination of motion, pulsatile flow and cros013), http://dx.doi.org/10.1016/j.mri.2013.03

© 2013 Elsevier Inc. All rights reserved.

1. Introduction

Magnetic resonance imaging (MRI) is the imaging technique ofchoice for the investigation of patients with documented primarytumours and suspected malignant infiltration of the spine [1].

s

Extradural compression of the spinal cord or cauda equina fromvertebral metastases has been widely reported in the literature[2–4]. Intradural extramedullary metastases are uncommon [5]although their incidence is felt to be increasing, possibly as a result ofthe longer survival times in patients with systemic metastaticdiseases [6]. Degenerative disc disease of the spine is one of the mostcommon clinical entities and the lumbar spine region is among themost commonly involved sites in severe primary spinal degenerativechanges [7].

In all the above clinical cases, especially when the diseases are ina more advanced stage (primary tumor, matastasis, degeneration

s-talk artifacts using blade sequences in lumbar.006

http://dx.doi.org/10.1016/j.mri.2013.03.006

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Table 1Summary of the sequences that were applied for lumbar spine MR examination.

Sequences T2-TSE-SAG T2-TSE-SAGBLADE

T2 TSE-AX T2 TSE-AXBLADE

TR (ms) 3500 6000 3610 6000TE (ms) 92 103 108 103Matrix (Freq/Phase) 384/288 256/256 384/288 256/256BW (Hz/pixel) 161 383 171 383Acquisition time (min) 4:03 3:08 4:25 3:08Thickness (mm) 4 4 4 4Space (%) 10 10 10 10ETL 34 35 24 30FOV (mm) 280/280 280/280 240/240 280/280Echo spacing (ms) 11.05 5.74 12 5.74Proportion of coverage - 130.4 - 130.4Number of signalaverages (NSA)

2.0 1.0 3.0 1.0

2 E. Lavdas et al. / Magnetic Resonance Imaging xxx (2013) xxx–xxx

etc.) the patient may often undergo MR examination under pain,which may result in lack of patient collaboration and undesirablepatient movements during the course of the examination. The use ofsagittal T2-weighted and axial T2-weighted sequences is a basicstarting point in the imaging of spinal discogenic diseases [8]. MR ofthe spine based on T2-weighted images can be performed withconventional spin echo (SE) or, preferably with fast spin echo (FSE)techniques [9–12]. FSE MR imaging sequences have a shorteracquisition time than the conventional SE imaging sequences.

MR imaging with BLADE, which is a PROPELLER-equivalentimplementation of the Siemens Medical System (Erlangen, Germa-ny), have been shown to effectively reducemotion and pulsatile flowartifacts [12–17]. The term BLADE is the product name of a brand’sTSE sequence that uses the PROPELLER (periodically rotated over-lapping parallel lines with enhanced reconstruction) k-spacetrajectory. The BLADE method acquires N blades (N number ofblades) that are rotated around the center of the k space. Each bladeconsists of L lowest phase encoding lines (i.e., echo train length[ETL]) of a conventional rectilinear k-space trajectory that areacquired after a single radiofrequency excitation. In brain MRimaging, it has been reported that the BLADE sequences reducemotion artifacts and improve image quality [18–22]. Recently, theBLADE technique was also used in examinations of the cervical spine,neck, upper abdomen, knee, kidneys and breast [23–29]. The BLADEtechnique has the advantage of central k-space oversampling, so thatimage artifacts are greatly reduced [18,23–30]. On the other hand, itis not yet confirmed how much motion and streak artifacts[21,23,31], which appear in radial scans [32], are reduced whendifferent BLADE parameters are employed [33].

In this study, T2 TSE AX and T2 TSE SAG BLADE sequences wereemployed in order to assess their ability to significantly reduce oreven eliminatemotion artifacts and improve image quality in lumbarspine MRI examinations.

2. Materials and methods

2.1. Patients

From March 2010 to April 2012, forty four patients (19 females,25 males; mean age 41 years, range 16–81 years), who had beenroutinely scanned for lumbar spine examination using four differentimage acquisition techniques, participated in the study. Morespecifically, the following pairs of sequences with and withoutBLADE were applied: a) T2 TSE SAG in thirty two patients, and b) T2TSE AXIAL in thirty two patients. This study was approved by thelocal institutional review board and written informed consent wasobtained from all the subjects participating in the study protocol.Due to practical limitations, both pairs of sequences were acquired in20 of the patients. Of the remaining group of 24 patients, one halfwas scanned using the TSE SAG BLADE sequence, whereas the otherhalf was scanned using the TSE AXIAL BLADE sequence.

2.2. MR imaging techniques

On all the patients, the lumbar spine MRI examinations wereperformed using a 1.5 T scanner (Magneton Avanto, SiemensHealthcare Sector, Erlangen, Germany) and a synergy bodyphased-array surface coil. The parameters of the different sequencesare presented in Table 1.

2.3. Quantitative analysis

A quantitative analysis was performed for the examined foursequences. In the quantitative analysis the following items were

Please cite this article as: Lavdas E, et al, Elimination of motion, pulsatile flow and cross-talk artifacts using blade sequences in lumbarspine MR imaging, Magn Reson Imaging (2013), http://dx.doi.org/10.1016/j.mri.2013.03.006

analyzed: (a) the signal-to-noise ratio (SNR) in spinal cord (SC),normal bone marrow (BM), neural root (NR), fatty tissue (FT),cerebrospinal fluid (CSF) and vertebral disk (VD) (b) the contrast-to-noise ratio (CNR) between the CSF and spinal cord, normal bonemarrow and vertebral disc, neural root and its surrounding fattytissue, CSF and normal bone marrow, CSF and vertebral disc,vertebral disk and neural root, and finally vertebral disk and fattytissue. For calculating these values, the signal intensity (SI) of thespinal cord, CSF, normal bone marrow, vertebral disc, neural root,fatty tissue and standard deviation (SD) of background noise weremeasured by placing regions of interest (ROIs). For each patient, theROIs were identical and were place in the same position in the twosequences under comparison. The SD of the background noise wasmeasured in the largest possible ROI positioned in the phase-encoding direction outside the abdominal wall (air) to account forany motion artifacts. When in some cases the positions of the ROIs ofone sequence were shifted due to patient motion, the ROIs weremanually placed based on their relative position to adjacent tissues.

The SNR was calculated as:

SNRA ¼ SIAN

ð1Þ

where A represents the tissue of interest, the SIA is the signalintensity of A measured by an elliptical region-of-interest (ROI) onthe system console. SI is taken as themean value throughout the ROI.N is the background noise, which was defined as the standarddeviation of a measurement.

The CNR was calculated as:

CNRAB ¼ SIA−SI BN

ð2Þ

where SIA and SIB define the SI of the tissues A and B, respectively.A fundamental requirement for any comparison of SNR or CNR

between two different sequences is that the resolution should bemade equivalent between the two methods. For this reason, the SNRand CNR values of the examined sequences were normalized by thecorresponding voxel sizes in order to account for the differences invoxel size.

The quantitative evaluation was performed by means of theKolmogorov-Smirnov non parametric test.

2.4. Qualitative analysis

All the images of the examined four MR sequences with andwithout BLADE were visually evaluated and compared indepen-dently at two separate examination sessions with 3 weeks interval


Table 2Summary of the results of the quantitative comparison between the BLADE and conventional sequences.

SNR T2-TSE-SAG T2-TSE-SAG BLADE p T2 TSE-AX T2 TSE-AX BLADE p

BM 55.7 ± 19.4 203.5 ± 57.5 b0.01 43.2 ± 18.1 235.8 ± 75.5 b0.01VD 29.1 ± 16.5 130.9 ± 82.2 b0.01 13.0 ± 5.6 86.2 ± 34.4 b0.01NR 53.3 ± 20.1 181.4 ± 59.0 b0.01 38.5 ± 43.9 177.1 ± 121.0 b0.01SC 63.8 ± 15.2 155.8 ± 33.4 b0.01 - - -CSF 133.8 ± 39.2 436.6 ± 113.3 b0.01 85.9 ± 36.4 406.0 ± 109.8 b0.01FT 55.7 ± 19.4 203.5 ± 57.5 b0.01 43.2 ± 18.1 235.8 ± 75.5 b0.01NS 166.1 ± 50.8 424.6 ± 113.2 b0.01 118.9 ± 43.4 441.7 ± 154.9 b0.01

CNR T2-TSE-SAG T2-TSE-SAG BLADE p T2 TSE-AX T2 TSE-AX BLADE p

BM/VD 29.2 ± 18.8 85.6 ± 47.1 b0.01 30.3 ± 17.3 151.7 ± 76.4 b0.01CSF/SC 102.3 ± 38.1 268.8 ± 87.6 b0.01 - - -NR/FT 80.6 ± 28.5 255.2 ± 91.8 b0.01 54.7 ± 26.6 229.2 ± 120.4 b0.01CSF/BM 110.4 ± 34.3 221.1 ± 85.9 b0.01 75.7 ± 35.4 205.9 ± 101.3 b0.01CSF/VD 137.0 ± 47.5 293.7 ± 111.2 b0.01 106.0 ± 41.1 355.5 ± 148.5 b0.01VD/NR 26.9 ± 18.7 81.3 ± 45.3 b0.01 25.8 ± 44.1 93.3 ± 123.7 b0.01VD/FT 104.7 ± 37.3 305.7 ± 108.7 b0.01 73.0 ± 34.1 319.8 ± 98.5 b0.01

The analysis of the signal to noise ratio (SNR) and contrast to noise ratio (CNR) results was performed using the Kolmogorov-Smirnov non parametric test.BM: bone marrow, VD: vertebral disc, NR: neural root, SC: spinal cord, NS: noise, CSF: cerebrospinal fluid, FT: fatty tissue.

3E. Lavdas et al. / Magnetic Resonance Imaging xxx (2013) xxx–xxx

by two experienced onMR imaging radiologists and the results of theblinded evaluations were used in the analysis.

The images from the corresponding sequences were filmed atoptimal window and level settings. It should be stated that window

Fig. 1. Sagittal T2 TSE (upper left), Sagittal T2 TSE BLADE (upper right), Axial T2 TSE (lower left) and Axial T2 TSE BLADE (lower right) images of the spine. It is shown that themotion artifacts that are seen in the T2 TSE sequences are eliminated in the T2 TSE BLADE sequences improving significantly the overall image quality.


settings have a dynamic width in MRI examinations and thosewindow and level settings are decided by the system itself. Theradiologists graded on a 5-point scale (0: non-visualization; 1: poor;2: average; 3: good; 4: excellent) each of the following image


Fig. 2. Sagittal T2 TSE (left) and sagittal T2 TSE BLADE (right) images of the lumbar spine. It is shown that the motion artifacts that are seen in the T2 TSE sequence are eliminatedthe T2 TSE BLADE sequence improving significantly the overall image quality.

ig. 3. Axial T2 TSE (upper left), Axial T2 TSE BLADE (upper right), Axial T2 TSE (lower left) and Axial T2 TSE BLADE (lower right) images of the spine. It is shown that the BLADEequences manage to minimize or even eliminate the initially observed cross-talk (lateral arrows) and pulsatile flow (central arrows) artifacts.


in

Fs




characteristics: (1) overall image quality, (2) conspicuousness of themorphologic abnormalities in the discovertebral junction, (3)conspicuousness of the nerve roots in the neural foramen, (4)contrast at the vertebral disc–CSF interface, (5) contrast at thevertebral disc–spinal cord (cauda equina) interface, (6) contrast atthe lesion of the vertebral body–bonemarrow and (7) contrast at thespinal cord (cauda equina)–CSF interface. The evaluators (radiolo-gists) also evaluated the presence of image motion, pulsatile flowand cross-talk artifacts using a separate scoring scale (0, maximum;1, severe; 2, moderate; 3, slight; 4, minimum).

3. Results

3.1. Quantitative results

The results of the quantitative analysis obtained from all thepatients are presented in Table 2.

It is observed that the BLADE sequences are superior to thecorresponding conventional ones in all the cases. Moreover, the

Fig. 4. Axial T2 TSE (upper left), Axial T2 TSE BLADE (upper right), Sagittal T2 TSE (lower lefvisualization of the intervertebral discs is achieved by the BLADE sequences. Especially, thebetter identified in the Axial BLADE sequence. Furthermore, in the Sagittal T2 TSE BLADE seqS1, is achieved.

Please cite this article as: Lavdas E, et al, Elimination of motion, pulsaspine MR imaging, Magn Reson Imaging (2013), http://dx.doi.org/10.1

results of the SNR and CNR comparisons show remarkablestatistically significant differences between the BLADE and theconventional sequences, especially in the SNR comparisons of T2TSE SAG for bone marrow, neural root, CSF, fatty tissue and those ofT2 TSE AX for bone marrow, vertebral disc, CSF and fatty tissue.Similarly, large statistically significant differences were found inthe CNR comparisons between CSF/spinal cord, neural root/fattytissue, vertebral disc/fatty tissue in T2 TSE SAG and bone marrow/vertebral disc, neural root/ fatty tissue, CSF/vertebral disc in T2 TSEAX between the BLADE and conventional sequences. Also, statis-tically significant differences were found in the SD in air resultsbetween the BLADE and conventional sequences.

3.2. Qualitative analysis

The results of the qualitative analysis obtained from allthe patients indicate that BLADE sequences were superior to thecorresponding conventional sequences in all the cases. Thestatistical significance of the qualitative data was determined by

t) and Sagittal T2 TSE BLADE (lower right) images of the spine. It is shown that a betterherniated disc that exists between the spinal sac and the normal vertebral disc can beuence a better visualization of the annular tear in the inter-vertebral disc between L5–

tile flow and cross-talk artifacts using blade sequences in lumbar016/j.mri.2013.03.006



the Kruskal–Wallis non-parametric test. More specifically,the qualitative analysis of motion artifacts based on the evaluationof the two experts gave a scoring of 2.70 ± 1.03 for the T2 TSESAG sequence against 3.56 ± 0.56 for the T2 TSE SAG BLADEsequence. Similarly, the score of the T2 TSE AX was 2.72 ± 1.05,whereas that of the T2 TSE AX BLADE was 3.69 ± 0.47. In bothcomparisons the differences were found to be statistically signif-icant (p b 0.01).

The T2 TSE SAG BLADE sequence was significantly superior thanthe corresponding conventional sequence in terms of: (1) overallimage quality (p b 0.01), (2) conspicuousness of the morphologicabnormalities in the discovertebral junction (p b 0.01), (3)conspicuousness of the nerve roots in the neural foramen(p b 0.01), (4) contrast at the vertebral disc–CSF interface(p b 0.01) and (5) contrast at the lesion of the vertebral body–bone marrow (p b 0.01).

Similarly, the results of the qualitative analysis indicate that theT2 TSE AX BLADE sequence was superior than the correspondingconventional sequence in all the examined factors. Specifically, (1)overall image quality (p b 0.01), (2) conspicuousness of themorphologic abnormalities in the discovertebral junction(p b 0.01), (3) conspicuousness of the nerve roots in the neuralforamen (p b 0.01), (4) contrast at the vertebral disc–spinal cord(cauda equina) interface (p b 0.01), and (5) contrast at the lesion of

ig. 5. Axial T2 TSE (upper left), Axial T2 TSE BLADE (upper right), Axial T2 TSE (lower left) and Axial T2 TSE BLADE (lower right) images of the lumbar spine. It is shown that bysing the BLADE sequences a better distinction between the neural roots, the fatty tissue (large arrow) and the joints (small arrow), is achieved. Furthermore, in the Axial T2 TSE

Fu
BLADE (lower right) sequence a better visualization of the annular tear in the inter-verte

the vertebral body–bone marrow (p b 0.01) were in favour of the T2TSE AX BLADE sequence.

Motion artifacts were shown in: a) seven T2 TSE SAG (Figs. 1 and2), and b) six T2 TSE AXIAL (Fig. 1) cases, respectively. Four of thesesequences were of no diagnostic value. However, when BLADEsequences were used, motion artifacts were eliminated.

Of the eleven patients, where pulsatile flow artifacts wereobserved, the T2 TSE AXIAL BLADE sequence managed to eliminatethem in six cases, whereas of the eleven patients, where cross-talkartifacts were observed, the T2 TSE AXIAL BLADE sequence managedto eliminate them in all the cases (Fig. 3).

The pathologies that were found in the conventional sequenceswere also found in the corresponding BLADE sequences. Morespecifically, a better visualization of the herniated disc between thespinal sac and the normal vertebral disc as well as of the annular dearin the inter-vertebral disc could be achieved (Figs. 4 and 5). A betterdistinction between the neural roots, the fatty tissue and the jointswere observed in the BLADE sequences (Fig. 5). Furthermore, theModic and in general the degenerative changes could be bettervisualized by the BLADE sequences (Fig. 6) [34,35].

However, the evaluators (radiologists) observed that in somecases where the T2 TSE AX conventional sequence was applied theneural roots in spinal canal were visualized more clearly comparedwith the T2 TSE AX BLADE sequence.

bral disc between, is achieved (small arrow) compared to Axial T2 TSE (lower left).



Fig. 6. Sagittal T2 TSE (upper left), Sagittal T2 TSE BLADE (upper right), Sagittal T2 TSE (lower left) and Sagittal T2 TSE BLADE (lower right) images of the spine. It is shown that theBLADE sequences achieve better visualization of the degenerative changes. More specifically, in the upper images it is shown that the Modic-II (arrows) in the inter-vertebral discbetween L5–S1, is better visualized by the BLADE sequence. Also, in the lower images, the degenerative changes (such as that shown by the arrows) are better distinguished fromtheir environment by the BLADE sequence.


4. Discussion

The diagnostic value of T2-weighted TSE SAGITAL and AXIALimages has been established in lumbar spine examination. However,in severe cases of primary tumor, matastasis, spine fractures anddegeneration, which cause compression of the spinal cord, caudaequina or peripheral nerves, there is presence of patient movementsproducing motion artifacts, which have as a consequence adegradation of image quality. Furthermore, motion artifacts canalso be observed in non-cooperative patients such as patients withParkinson’s disease, patients with brain damages (tumor, metastasis,ischemic lesions etc.), small children, bone fractures etc. In brain MRimaging, it has been reported that the BLADE sequences reducemotion artifacts and improve image quality [16–20].

Motion artifacts appear as hypo-intense lines in the central tissuein the phase encoding direction thereby reducing image quality tolevels that are often characterized by radiologists as being of non-diagnostic value.

The artifacts cross-talk is very common in the examination oflumbar spine. Selective RF pulses yield imperfect slice profiles,whose edges are not clearly cut. In multislice techniques withcontiguous slices, a selective RF pulse can thus partially excite theadjacent slices. Likewise, if several interlacing slice stacks cross, the


zone of intersection will be partially excited. This will cause amodification in contrast and/or a loss of signal through partialsaturation in the slice or zone of intersection. These phenomena areeven more pronounced when pulses of 180° are used (inversionrecovery, fast spin echo or turbo spin echo).

The solution consists in spacing the slices by adding an intervalbetween them: the slices are no longer contiguous. It is also possible tointerlace multislice acquisition to avoid imaging the adjacent sliceswith the same repetition time. In the cases where it is vital to visualizethe whole volume with no wasted time, it is preferable to use 3Dsequences. In lumbar spine examinations, T2 TSE AXIAL sequencecommonly covers only the intervertebral space so it is not possible toincrease the interval between the slices because this would cause lossof valuable information. Furthermore, 3D sequences are not practicalto be applied for imaging each intervertebral space. The effectivereduction of the cross-talk artifacts is a feature of the BLADE technique.This is based on the fact that although the reduction of those artifactsstems from the use of long TR values, these long TR values are possibleto be applied due to the characteristics of the BLADE technique.Otherwise, the overall acquisition time would be significantly largerleading to a deterioration of image quality.

BLADE technique has been found to reduce motion artifacts inexaminations of the brain, cervical spine, neck, upper abdomen, knee,




kidneys and breast [22–29]. Due to the fact that in lumbar spineexaminationsmotion artifacts were often observed, we decided to useBLADE sequences in order to examine whether they can eliminatethose motion as well as pulsatile flow and cross-talk artifacts and ifthey have any impact in the visualization of the nearby tissues.

Siemens Healthcare Sector has not yet prepared BLADE se-quences for lumbar spine to provide during the installation of theirsystems. In this study, the T2 TSE SAG BLADE sequence from cervicalspine protocol of Siemens Healthcare Sector was employed, in whichthe values of FOV, Slice Thickness and Space were modified in orderto match those of the T2 TSE SAG sequence from lumbar spineprotocol. For producing the T2 TSE AX BLADE sequence, thepreviously described T2 TSE SAG BLADE sequence was used as abasis, in which the values of Slice Thickness and Space weremodifiedto match those of the T2 TSE AX sequence from lumbar spineprotocol. In the BLADE sequences, the FOV was set to280 mm × 280 mm, whereas in the T2 TSE sequences it was240 mm × 240 mm. This was done in order to visualize a largerarea of the soft tissue, aorta and kidney and because in this way abetter SNR (lower noise) could be achieved. For this reason, the SNRand CNR values of the examined sequences were normalized by thecorresponding voxel sizes in order to account for the differences invoxel size and make the relevant comparisons compatible.

The BLADE sequences are commonly applied with higher echotraining length comparedwith conventional sequences. In one of ourprevious studies, it was found that the T2 TSE AXIAL BLADEsequence, which was applied in brain imaging with a lower echotraining length compared with the conventional T2 TSE AXIAL,managed to eliminate motion and pulsatile flow artifacts withoutdecreasing image quality [22]. The same approachwas applied in theexamined lumbar spine examinations where the T2 TSE SAG BLADEsequence has an ETL of 35, whereas the T2 TSE SAG conversionalsequence has an ETL equal to 34. The ETL is significant factor becauseit directly affects the acquisition time.

In the BLADE sequences, the acquisition time is normallyincreased compared with the conventional sequences. However,the T2 TSE AX BLADE sequence which is applied in this study has adecreased acquisition time (3:08 min:sec) compared with thecorresponding conventional sequence (4:25). Similarly, the T2 TSESAG BLADE sequence has an acquisition time of 3:08, whereas the T2TSE SAG conversional sequence has 4:03. This is a great advantagebecause it allows us to increase the matrix and the blade coverage,which results in a further enhancement of image quality. Also, byincreasing the size of the matrix it is possible to reduce the onlydisadvantage that was found in the T2 TSE AX BLADE sequences inthe visualization of neural roots in spinal canal.

3 T MR imaging has a double SNR compared with 1.5 T. However,more artifacts are commonly observed in 3 T compared with 1.5 Tsystems. In 3 T MRI systems, the possibility of increasing the size ofthe matrix without causing a SNR decrease and scan time increase(compared with the values applied in the 1.5 T systems) is exploitedleading to a two-fold gain since: a) BLADE sequences can eliminatethe artifacts (which is significant problem in 3 T), and b) theincreased SNR can provide high image quality.

In our results, it was found that BLADE sequences eliminatedmotion artifacts in all the cases. More specifically, the motionartifacts that were observed in seven T2 TSE SAG and six T2 TSEAXIAL cases, respectively were eliminated by the correspondingBLADE sequences improving significantly the overall image quality(Figs. 1 and 2). It is important to mention that although four of thesecases were of no diagnostic value when the conventional sequencewas used, the necessary diagnostic information was possible to beacquired when the BLADE sequences were applied.

Regarding pulsatile flow and cross-talk artifacts it is shown thatthe BLADE sequences manage to minimize or even eliminate them.


More specifically, in eleven cases where pulsatile flow artifacts wereobserved, the T2 TSE AXIAL BLADE sequence managed to eliminatethem in six of those cases. On the other hand, the T2 TSE AXIALBLADE sequence managed to eliminate the cross-talk artifacts in allthe cases where those artifacts were observed (Fig. 3).

Another good achievement of the BLADE sequences is the bettervisualization of the intervertebral discs. Especially, the herniated discand the normal vertebral disc can be better identified in the AxialBLADE sequence. Additionally, the Sagittal T2 TSE BLADE sequenceachieved a better visualization of the annular tear in the inter-vertebral disc (Figs. 4 and 5). The BLADE sequences provided a betterdistinction between the neural roots, the fatty tissue and the jointstoo (Fig. 5). Finally, by using the BLADE sequences, the Modic isbetter visualized and the degenerative changes are better distin-guished from their environment (Fig. 6).

Apart from the fact that BLADE sequences eliminate motionartifacts, they are associated with a higher SNR in bone marrow,vertebral disk, neural roots and fatty tissue. Also, image quality ishigher in BLADE sequences and one of the reasons is becausethey use a larger bandwidth than the conventional sequences,which may have as a consequence the reduction of chemical shiftartifacts [36].

Another significant finding of this study is the lower SD in air,whichwas observed in all the patients. In two of our previous studiesit had been found that in brain and knee MRI examinations, theBLADE sequences could achieve a lower SD only in uncooperativegroups of patients [22,27]. This finding of the present study stemsfrom the fact that the anterior abdominal wall moves due tobreathing and it produces motion artifacts, which are not eliminatedby the Rest slabs (Regional Saturation Technique) that arecommonly used in lumbar spine examinations. In Table 2, it isshown that the noise (N) (which is the standard deviation) of theBLADE and conventional sequences differ statistically significant. Themotion artifacts in the background of the conventional sequences arelarger than those in the BLADE sequences and this is a significantfactor contributing to the larger SNR values of the latter sequences.Since these artifacts are shown in the background they will affect theoverall image quality.

Also this finding agrees with the findings of Bayramoglu et al.[23], who found that the SNR values of BLADE sequences that wereapplied in liver and gallbladder examinations were significantlylower than those of the corresponding TSE sequences that usedbreath-hold and free-breathing navigator-triggered techniques. Themean background noise was not significantly lower in all theexamined sequences perhaps due to the breath-hold and free-breathing navigator-triggered techniques, which also reduce motionartifacts and consequently the mean background noise. However,these breath-hold and free-breathing navigator-triggered tech-niques cannot be applied in lumbar spine examinations.

However, regarding the SNR and CNR comparisons between theBLADE and the conventional sequences, it should be clarified thatthey are not compatible. The much higher SNR and CNR values of theBLADE sequences compared to the conventional ones mainly stemfrom the ability of the BLADE sequences to significantly reduce oreliminate themotion and flow artifacts. Thismeans that the reportedSNR and CNR values of the BLADE sequences do not stem solely fromtheir intrinsic characteristics. The noise in a magnitude MRI image isRician distributed. Its mean and standard deviation should notsubstantially change regardless of where in the air the ROI is drawn[37]. However, artifacts will vary in amplitude and compositionacross the image. This will result in a very different standarddeviation value depending on where the ROI is drawn. Although themethod that has been employed in the present study to estimate theSNR and CNR values is commonly used, it is only valid in the absenceof artifacts.




The combination of longer scan time and signal averagingtogether with the other reported parameters of the conventionalsequences should normally yield higher SNR values compared to theBLADE sequences. However, the BLADE sequences produce signifi-cantly fewer motion and flow artifacts than the conventionalsequences and this is reflected in the SNR and CNR measurements.So, the SNR and CNR findings of this study should be treated more asanother way of expressing the ability of the BLADE sequences toreduce or eliminate the motion and flow artifacts rather than as amean to perform absolute comparisons with the conventionalsequences. In line with this analysis, it would be very interestingto study the relationship of the SNR and CNR values as a function ofartifact reduction.

In clinical practice, this is considered to be very importantbecause in two cases annular tear was observed (Fig. 4). Also, inmostof the caseswe could distinguish better the borders of the nerve fromthe fatty tissue in the region of spinal foramen. Especially in one case,the conventional sequences showed that the two nerves were incontact with the disk, whereas the BLADE sequences showed that thedisk were in contact only with the right nerve and this finding wasverified by the clinical symptoms of the patient (Fig. 4).

Based on the findings of the present study, it is expected that theuse of BLADE sequences also in thoracic spine examinations couldimprove image quality due to the extensive breathing motions inthis anatomical site.

It was observed that in the T2 TSE AX BLADE sequence the neuralroot is shown as being smaller in size compared with theconventional sequence. This finding is explained by the fact thatthe BLADE sequence can distinguish the neural root from the rootvessel. This finding agrees with findings from previous studies inknee and brain MR examinations [14], where it was observed that abetter visualization of the vessels could be achieved by BLADEsequences, which led us to propose the use of BLADE-basedtechniques in angiographies.

In conclusion, the use of BLADE sequences in lumbar spine MRexaminations appears to be capable of potentially eliminatingmotion, pulsatile flow and cross-talk artifacts. However, the valuesof the different parameters (ETL, bandwidth, matrix size, bladecoverage) have to be examined in order to optimize even moreimage quality and image acquisition time. Furthermore, we proposethe use of BLADE sequences in the standard examination protocolsbased on the fact that a significantly improved image quality couldbe achieved.

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