Rationale and Objectives
The purpose of this study was to evaluate the feasibility and technical quality of a zoomed three-dimensional (3D) turbo spin-echo (TSE) sampling perfection with application optimized contrasts using different flip-angle evolutions (SPACE) sequence of the lumbar spine.
Materials and Methods
In this prospective feasibility study, nine volunteers underwent a 3-T magnetic resonance examination of the lumbar spine including 1) a conventional 3D T2-weighted (T2w) SPACE sequence with generalized autocalibrating partially parallel acquisition technique acceleration factor 2 and 2) a zoomed 3D T2w SPACE sequence with a reduced field of view (reduction factor 2). Images were evaluated with regard to image sharpness, signal homogeneity, and the presence of artifacts by two experienced radiologists. For quantitative analysis, signal-to-noise ratio (SNR) values were calculated.
Results
Image sharpness of anatomic structures was statistically significantly greater with zoomed SPACE ( P < .0001), whereas the signal homogeneity was statistically significantly greater with conventional SPACE (cSPACE; P = .0003). There were no statistically significant differences in extent of artifacts. Acquisition times were 8:20 minutes for cSPACE and 6:30 minutes for zoomed SPACE. Readers 1 and 2 selected zSPACE as the preferred sequence in five of nine cases. In two of nine cases, both sequences were rated as equally preferred by both the readers. SNR values were statistically significantly greater with cSPACE.
Conclusions
In comparison to a cSPACE sequences, zoomed SPACE imaging of the lumbar spine provides sharper images in conjunction with a 25% reduction in acquisition time.
Magnetic resonance imaging (MRI) is the modality of choice for evaluation of the spine and degenerative disc disease because of its excellent soft tissue contrast. T2-weighted (T2W), two-dimensional (2D), turbo spin-echo (TSE) sequences provide high contrast between anatomic structures enabling reliable visualization of spinal lesions and pathologic changes within the intervertebral discs . Nevertheless, with 2D sequences, through-plane resolution is limited because of signal-to-noise ratio (SNR) loss, increases in examination time, and cross-talk artifact. The latter further reduces SNR and alters image contrast .
Conventional, fast 3D imaging techniques are primarily based on gradient-echo pulse sequences that result in T1 or T2* contrast. However, adequate T2 contrast is required for the diagnosis of degenerative spine disorders, a condition present in a large proportion of examinations performed in the daily clinical routine . Although adequate image contrast is achievable with gradient-echo magnetic resonance (MR) sequences (eg, multi echo data image combination (MEDIC) or double-echo steady state (DESS) sequences) , a spin-echo or TSE sequence provides optimal T2 contrast. At 3 T, spin-echo–based techniques are limited by high specific absorption rates (SARs). Such SAR considerations have encouraged the development of a three-dimensional (3D), T2w, TSE sequence with variable flip angles along the echo train (sampling perfection with application optimized contrasts using different flip-angle evolutions [SPACE]) . Three-dimensional sequences with isotropic spatial resolution enable high-quality reformatted images in arbitrary spatial orientations, potentially improving diagnostic performance. Three-dimensional T2w SPACE has been shown to be clinically feasible for high-resolution imaging of the cervical spine and superior to conventional 2D T2w TSE imaging in the delineation of anatomic details in that region .
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Materials and methods
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Image Acquisition
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Table 1
Imaging Parameters for the Volunteer and Patient Populations
Sequence Type cSPACE zSPACE 3D SPACE TR/TE (ms) 1700/138 1700/138 FOV (mm 2 ) 300 × 300 150 × 320 Matrix 304 × 320 160 × 320 Slice thickness (mm) 0.9 0.9 In-plane resolution (mm 2 ) 0.9 × 0.9 0.9 × 0.9 Phase-encoding direction Head–feet Anterior–posterior Phase-encoding steps 433 166 Parallel imaging GRAPPA2 — Acquisition time (min) 8:20 6:30 Averages 2 2 Flip angle 100° 100° Bandwidth (Hz/px) 380 380
3D, three-dimensional; cSPACE, conventional SPACE; FOV, field of view; GRAPPA, generalized autocalibrating partially parallel acquisition technique; SPACE, sampling perfection with application optimized contrasts using different flip-angle evolutions; TE, echo time; TR, repetition time; zSPACE, zoomed SPACE.
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Image Analysis
Qualitative Image analysis
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Quantitative Image Analysis
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Statistical Analysis
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Results
Qualitative Image Analysis
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Table 2
Image Quality Scores (Median) of Both Sequences
Image quality parameters cSPACE zSPACE Sharpness 2 3 Image homogeneity 3 2 Artifacts 3 3
cSPACE, conventional SPACE; SPACE, sampling perfection with application optimized contrasts using different flip-angle evolutions; zSPACE, zoomed SPACE.
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Quantitative Image Analysis
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Discussion
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Conclusions
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