Rationale and Objectives
The aim of this study was to compare four different fat-suppressed T2-weighted sequences with different techniques with regard to image quality and lesion detection in upper abdominal magnetic resonance imaging (MRI) scans.
Materials and Methods
Thirty-two consecutive patients referred for upper abdominal MRI for the evaluation of various suspected pathologies were included in this study. Different T2-weighted sequences (free-breathing navigator-triggered turbo spin-echo [TSE], free-breathing navigator-triggered TSE with restore pulse (RP), breath-hold TSE with RP, and free-breathing navigator-triggered TSE with RP using the periodically rotated overlapping parallel lines with enhanced reconstruction technique [using BLADE, a Siemens implementation of this technique]) were used on all patients. All images were assessed independently by two radiologists. Assessments of motion artifacts; the edge sharpness of the liver, pancreas, and intrahepatic vessels; depictions of the intrahepatic vessels; and overall image quality were performed qualitatively. Quantitative analysis was performed by calculation of the signal-to-noise ratios for liver tissue and gallbladder as well as contrast-to-noise ratios of liver to spleen.
Results
Liver and gallbladder signal-to-noise ratios as well as liver to spleen contrast-to-noise ratios were significantly higher ( P < .05) for the BLADE technique compared to all other sequences. In qualitative analysis, the severity of motion artifacts was significantly lower with T2-weighted free-breathing navigator-triggered BLADE sequences compared to other sequences ( P < .01). The edge sharpness of the liver, pancreas, and intrahepatic vessels; depictions of the intrahepatic vessels; and overall image quality were significantly better with the BLADE sequence ( P < .05).
Conclusion
The T2-weighted free-breathing navigator-triggered TSE sequence with the BLADE technique is a promising approach for reducing motion artifacts and improving image quality in upper abdominal MRI scans.
For liver magnetic resonance imaging (MRI), high-quality T2-weighted (T2W) images are necessary for the detection and characterization of focal hepatic lesions. Various MRI techniques have been investigated to achieve optimal image quality . Recent technical developments such as powerful gradient systems and receiver coils with higher sensitivities have significantly enhanced image quality. However, motion artifacts remain a central problem of upper abdominal MRI scans, being the main cause of image quality degradation, and great efforts have been made to achieve high-quality T2W images without motion artifacts. Today, T2W turbo spin-echo (TSE) sequences are generally considered to be the standard imaging sequence for the evaluation of liver parenchyma. Breath-hold (BH) imaging with rapid imaging techniques has been a useful method that can reduce respiratory motion artifacts, providing shorter acquisition times and thereby increasing patient compliance and throughput. TSE and half-Fourier acquisition single-shot TSE are widely used methods of BH T2W imaging that permit scanning of the entire liver in a single or a few BH steps .
Another approach for reducing respiratory motion artifacts is to use triggering techniques that synchronize anatomic data acquisition with the respiratory cycle using a belt placed on the patient’s abdomen . Respiratory triggering techniques provide high tissue contrast and allow images to be obtained at thin slice thicknesses.
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Materials and methods
Patients
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MRI Protocol
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Table 1
Summary of Imaging Parameters for Each Fat-suppressed T2W Sequence
Parameter T2W-PACE ∗ -TSE with RP T2W-PACE-TSE BH-T2W-TSE with RP T2W-BLADE ∗ with PACE and RP Repetition time (ms) 4600 4600 3400 4000 Echo time (ms) 90 90 90 100 Matrix (frequency × phase) 320 × 153 320 × 153 256 × 129 256 Field of view (%) 350 × 260–300 350 × 260–300 350 × 260–300 350 × 350 Bandwidth (kHz) 260 260 260 362 Turbo factor 19 19 27 35 Flip angle (°) 150 150 150 150 Number of signals acquired 2 2 1 1 Number of sections acquired 35 35 24 35
BH, breath-hold; PACE, Prospective Acquisition Correction; RP, restore pulse; TSE, turbo spin-echo; T2W, T2-weighted.
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Image Analysis
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Qualitative Evaluation
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Quantitative Evaluation
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Statistical Analysis
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Results
Qualitative Analysis
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Table 2
Results of Image Data Analysis for Each Fat-suppressed T2W Sequence
Sequence Motion Artifacts Edge Sharpness of Liver, Pancreas, and Intrahepatic Vessels Depiction of Intrahepatic Vessels Overall Image Quality Reader 1 T2W-PACE † -TSE with RP 3.88 ± 0.52 4.12 ± 0.43 4.20 ± 0.50 4.20 ± 0.40 T2W-PACE-TSE 3.74 ± 0.48 4.00 ± 0.50 4.00 ± 0.64 4.04 ± 0.35 BH-T2W-TSE with RP 3.24 ± 0.43 3.40 ± 0.50 3.52 ± 0.50 3.56 ± 0.50 T2W-BLADE † with PACE and RP 4.84 ± 0.47 4.92 ± 0.40 4.88 ± 0.33 4.96 ± 0.20P ∗ P 2 – P 6 < .01 ∗ P 2 – P 6 < .01 ∗ P 1 – P 6 < .01 ∗ P 2 – P 6 < .01P 1 > .05P 1 > .05P 1 > .05 Reader 2 T2W-PACE-TSE with RP 3.80 ± 0.40 4.04 ± 0.53 4.28 ± 0.45 4.24 ± 0.43 T2W-PACE-TSE 3.68 ± 0.55 3.92 ± 0.57 4.04 ± 0.61 4.04 ± 0.45 BH-T2W-TSE with RP 3.32 ± 0.47 3.34 ± 0.47 3.60 ± 0.50 3.52 ± 0.50 T2W-BLADE with PACE and RP 4.92 ± 0.27 4.84 ± 0.47 4.84 ± 0.37 4.88 ± 0.43P ∗ P 2 – P 6 < .01 ∗ P 2 – P 6 < .01 ∗ P 1 – P 6 < .01 ∗ P 1 – P 6 < .01P 1 > .05P 1 > .05
BH, breath-hold; P 1 , P value between first and second sequences; P 2 , P value between first and fourth sequences; P 3 , P value between first and third sequences; P 4 , P value between second and fourth sequences; P 5 , P value between second and third sequences; P 6 , P value between third and fourth sequences; PACE, Prospective Acquisition Correction; RP, restore pulse; TSE, turbo spin-echo; T2W, T2-weighted.
Data are expressed as mean ± standard deviation.
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Table 3
Results of Cohen’s κ Statistical Analysis of Motion Artifacts, Edge Sharpness of the Liver and Pancreas, Depiction and Sharpness of Intrahepatic Vessels, and Overall Image Quality Between Readers
Parameter κ Motion artifacts 88.2% Edge sharpness of liver, pancreas, and intrahepatic vessels 84.5% Depiction of intrahepatic vessels 86.6% Overall image quality 85.9%
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Quantitative Analysis
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Table 4
Results of Quantitative Assessment of Background Noise, Liver SNR, Liver-to-Spleen CNR, and Gallbladder SNR
Sequence Background Noise Liver SNR Liver-to-Spleen CNR Gallbladder SNR T2W-PACE ∗ -TSE with RP 2.2 ± 0.6 65.4 ± 22.8 72.4 ± 34.5 372.9 ± 137.9 T2W-PACE-TSE 2.3 ± 0.7 58.2 ± 20.7 65.1 ± 24.4 317.4 ± 109.5 T2W-BLADE ∗ with PACE and RP 2.2 ± 0.8 84.0 ± 31.5 84.0 ± 35.1 420.2 ± 131.7 BH-T2W-TSE with RP 2.0 ± 0.6 56.2 ± 26.8 63.7 ± 36.4 299.8 ± 136.7
BH, breath-hold; CNR, contrast-to-noise ratio; PACE, Prospective Acquisition Correction; RP, restore pulse; SNR, signal-to-noise ratio; TSE, turbo spin-echo; T2W, T2-weighted.
Data are expressed as mean ± standard deviation.
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Table 5
Differences Between Sequences in Terms of Background Noise, Liver SNR, Liver-to-Spleen CNR, and Gallbladder SNR
Comparison Background Noise ( P ) Liver SNR ( P ) Liver-to-Spleen CNR ( P ) Gallbladder SNR ( P ) T2W-BLADE ∗ with PACE ∗ and RP vs T2W-PACE-TSE with RP <.001 <.001 <.001 .08 T2W-BLADE with PACE and RP vs T2W-PACE-TSE <.001 <.001 <.001 <.01 T2W-BLADE with PACE and RP vs BH-T2W-TSE with RP <.001 <.001 <.001 <.001 T2W-PACE-TSE with RP vs T2W-PACE-TSE <.001 <.001 .07 <.001 T2W-PACE-TSE with RP vs BH-T2W-TSE with RP <.05 <.05 <.05 <.001 T2W-PACE-TSE vs BH-T2W-TSE with RP .740 .74 .45 .22
BH, breath-hold; CNR, contrast-to-noise ratio; PACE, Prospective Acquisition Correction; RP, restore pulse; SNR, signal-to-noise ratio; TSE, turbo spin-echo; T2W, T2-weighted.
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Discussion
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