Deep vein thrombosis (DVT) is a common but elusive illness that can lead to fatal pulmonary embolism and sudden death. Effective treatment of DVT requires accurate evaluation of thrombus distribution and stage. Ultrasonography (US) is typically used for the diagnosis of DVT, but its sensitivity is operator dependent and thrombus staging is impossible with US. MRI is an alternative diagnostic imaging modality, and two conventional methods are MPRAGE [1] and contrast-enhanced MR venography (CE-MRV) [2]. Recently, 3D T1-weigted variable-flip-angle turbo spin-echo (SPACE), was proposed for the detection of DVT [3]. However, signal suppression of tremendously slow venous blood flow remains a challenge for SPACE. The unsuppressed blood signal could be a confounder in thrombus identification [3]. To address this issue, we developed a 3D black-blood thrombus imaging (BTI) technique [4] that combines SPACE with DANTE black-blood preparation [5] (DANTE-SPACE) for the cerebral venous sinus system. In this work, we further accommodated the technique to the deep vein system and conducted preliminary clinical validation

Experiment: The DANTE-SPACE sequence was first optimized on 11 healthy subjects (6F 5M, age 25±3) on a 3T system (Tim Trio, Siemens, Germany) with two standard 12-channel coils positioned anteriorly and an integrated spine coil located posteriorly. Eight scans with different DANTE pulse train lengths (0, 50, 75, 100, 125, 150, 175, 200) were conducted with all other parameters held fixed (flip angle 15°, RF gap 1 ms, gradient strength 20 mT/m). Imaging parameters for SPACE readout included: 3D coronal scan with a 352-mm craniocaudal coverage , isotropic resolution of 1.1×1.1×1.1 mm3 (interpolated to 0.55×0.55×0.55 mm3), TR/TE 650/9.8 ms(imparting T1-weighted contrast), echo train length 40, GRAPPA factor 2, partial Fourier 6/8, scan time 4min47sec. The optimized sequence was then tested on 12 patients (6F 6M, age 52±13) with subacute to chronic DVT. The scan was targeted to the thrombus region that was pre-determined by US within 3 days. Conventional SPACE, MPRAGE, and CE-MRV were also conducted for comparison.

Image Analysis: Two radiologists evaluated randomized images and gave the diagnosis confidence scores (1–poor, 4–excellent) to each technique independently. The sensitivity (SE), specificity (SP), positive and negative predictive values (PPV and NPV), and the accuracy (ACC) of DANTE-SPACE, SPACE, and MPRAGE were calculated in detecting DVT using CE-MRV as the reference. The diagnostic agreement between DANTE-SPACE/SPACE/MPRAGE and CE-MRV and the interobserver agreement were assessed using Cohen κ test.

According to contrast-to-noise ratio (CNR) analysis, DANTE with 125-175 pulses appeared to be a suitable preparation to yield sufficient blood flow suppression without considerable signal loss in static tissues (Fig. 1). The DANTE with 175 pulses was thus chosen for the following patient study. Compared to conventional SPACE, the optimized DANTE-SPACE sequence effectively nulled the residual blood that would otherwise be mistaken as part of thrombus (Fig. 2). In contrast to MPRAGE that is only sensitive to the acute or sub-acute thrombus (Fig. 3b), DANTE-SPACE was able to depict the DVT regardless of the thrombus stage. The thrombus detected by DANTE-SPACE matched nicely with that by CE-MRV (Fig. 3a&c). A total of 112 venous segments were analyzed. DANTE-SPACE provided the highest diagnosis confidence score, when compared to SPACE and MPRAGE, and high SE, SP, PPV, NPV and ACC (Table 1). DANTE-SPACE is a BTI technique providing excellent venous blood signal suppression and definitive thrombus detection. The preliminary patient study has demonstrated that the technique may outperform conventional SPACE, MPRAGE, and become a non-contrast alternative to CEMRV for the diagnosis of DVT.