Synopsis

The study evaluate the diagnostic performance of SPACE MR sequence in detecting lower extremity deep venous thrombosis (DVT) and evaluating clot burden, with comparison to ultrasound (US). The result showed that SPACE MR is highly accurate in detecting lower extremity DVT and reliable in the evaluation of clot burden, thus could be considered as an important alternative for patients in whom US cannot be performed.

Purpose: To evaluate the diagnostic performance of MRI utilizing Sampling Perfection Application with contrast optimized using variable flip Angle Evolutions (SPACE) in detecting lower extremity deep venous thrombosis (DVT) and evaluating clot burden.

Method: This prospective study was approved by the institutional review board. 94 consecutive patients (male 42, female 52, age range 14-87 years, average age 52.7 years) suspected of lower extremity DVT underwent ultrasound (US) and MRI. MRI examinations were performed on a 3T scanner (Magnetom Skyra, Siemens Healthcare, Germany) with a combination of a 32-channel dedicated extremity coil and a 8-channel body matrix array coil. The SPACE sequence was scaned with the following protocol: TR/TE, 3200/100 ms; acquisition matrix, 384×306; FOV, 448×287 mm2; slice thickness, 1.2 mm; echo train length, 100. The sequence was performed with three consecutive stations to cover the lower extremity veins, and each station contains 32-50 slices with more than 2 cm overlap for adjacent station. The venous visualization score with SPACE MR was determined by two experienced radiologists with 4 levels (1-4, poor - excellent), then the diagnosis sensitivity and specificity of SPACE MR in detecting DVT was calculated based on segment, limb, and patient respectively, with ultrasound as the reference standard. Clot burden for each segment was scored (0-3, patent to entire segment occlusion) by SPACE MR and US independently, and their results was then compared using a Wilcoxon test based on region, limb, and patient respectively. Inter-observer agreement in assessing thrombosis (absent, non-occlusive, or occlusive) with SPACE MR was determined by calculating Cohen’s kappa coefficients.

Results:The mean venous visualization score with SPACE MR was 3.82±0.50 for Reader 1 and 3.81±0.50 for Reader 2. The sensitivity/specificity of SPACE in detecting DVT were respectively 97.89%/99.90% per segment, 98.77%/99.07% per limb, and 98.59%/95.65% per patient. For Reader 2, respective values were 98.58%/99.90%, 100%/99.07%, and 100%/95.83%. The burden of clot assessed with SPACE MR was not statistically significantly different from that assessed with US on either region, limb, or patient basis (P＞0.05). Interobserver agreement with SPACE MR was excellent (kappa=0.894±0.014) in assessing thrombosis.

Conclusion: SPACE MR is highly accurate in detecting lower extremity DVT and reliable in the evaluation of clot burden. SPACE MR could serve as an important alternative for patients in whom US cannot be performed.

Keywords: lower extremity; deep venous thrombosis; ultrasound; sensitivity; specificity; clot burden.

Acknowledgements

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