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The effect of using shorter echo times in MR imaging of knee menisci: a study using a porcine model
1Department of Diagnostic Radiology, The University of Hong Kong, Queen Mary Hospital, Hong Kong.
Objective:
Increasingly shorter TEs are being used for T1-weighted and proton density-weighted sequences in MR imaging of the knee. This study aims to evaluate the effect of a short TE on meniscal signal intensity.
Materials And Methods:
Thirty porcine knees were imaged with a 1.5-T MR scanner using spin-echo T1-weighted and proton density-weighted sequences. TR was kept constant at 700 msec for T1-weighted and 2200 msec for proton density-weighted sequences. For each set of sequences, sagittal images were obtained using these TE values: 9, 12, 16, 20, and 25 msec. Imaging parameters, such as slice thickness and interslice gap, number of excitations, matrix size, and field of view, were identical for each set of sequences. Using a fixed window level and width, we assessed the anterior and posterior horns of the medial meniscus for signal hyperintensity at each TE value. Signal intensity was also measured in eight knees. The menisci were then dissected and examined grossly and histopathologically.
Results:
Intrameniscal signal intensity increased progressively with shorter TEs. At a TE of 9 msec, signal hyperintensity was present in 100% of T1-weighted and 96.7% of proton density-weighted images. At a TE of 12 msec, signal hyperintensity was seen in 86.7% of T1-weighted and 80% of proton density-weighted images. At a TE of 16 msec, increased signal intensity was seen in only 3.3% of T1-weighted and 6.6% of proton density-weighted images. At TEs of 20 and 25 msec, increased signal intensity was seen in none of the T1-weighted and proton density-weighted images. Meniscal signal intensity increased exponentially at very short TE values. All menisci were found to be normal on gross and histopathological examination.
Conclusion:
Spurious signal hyperintensity appears in normal menisci at short TE values. Images acquired with short TEs should be interpreted with caution, and a TE of 16 msec or more is recommended.
Insights
Short echo times (TE) in MRI can cause artificial signal hyperintensity in normal menisci. Radiologists should use caution when interpreting knee MR images with short TE values, recommending a TE of 16 ms or higher.
Area of Science:
- Radiology
- Medical Imaging
- Orthopedic Imaging
Background:
- Magnetic Resonance (MR) imaging is crucial for knee joint evaluation.
- Shorter echo times (TE) are increasingly utilized in T1-weighted and proton density-weighted sequences.
- The impact of short TE on meniscal signal intensity requires careful assessment.
Purpose of the Study:
- To investigate the effect of varying short echo times (TE) on meniscal signal intensity in knee MR imaging.
- To determine the threshold TE for minimizing spurious signal hyperintensity in normal menisci.
Main Methods:
- Thirty porcine knees were imaged using a 1.5-T MR scanner.
- Spin-echo T1-weighted and proton density-weighted sequences were acquired with TE values of 9, 12, 16, 20, and 25 ms.
- Meniscal signal hyperintensity was assessed, and signal intensity was quantitatively measured. Gross and histopathological examinations were performed.
Main Results:
- Intrameniscal signal intensity increased progressively as TE decreased.
- Signal hyperintensity was observed in 100% of T1-weighted and 96.7% of proton density-weighted images at a TE of 9 ms.
- At a TE of 16 ms, signal hyperintensity decreased significantly (3.3% T1-weighted, 6.6% proton density-weighted), and was absent at 20 and 25 ms.
Conclusions:
- Short echo times (TE) can induce spurious signal hyperintensity in normal menisci.
- Interpretation of knee MR images acquired with short TE values necessitates caution.
- A TE of 16 ms or greater is recommended to avoid artifactual meniscal signal changes.