Susceptibility weighted magnetic resonance imaging of brain: A multifaceted powerful sequence that adds to understanding of acute stroke

Simultaneous depiction of clot and MRA using 1 min phase contrast angiography in acute ischemic patients

[Background and Purpose] Clot location and range predict clinical outcomes for acute ischemic stroke (AIS). We developed a new technique for visualizing occlusion clots, namely, the DEpicting blood clot and MRA using Phase contrast angiography with Image Calculation for Thrombectomy (DEPICT) method. The purpose of this study was to assess the clinical usefulness of DEPICT. [Methods] We used DEPICT in 36 AIS patients to obtain MRA and black blood images with 1-min phase contrast angiography (PCA). We created the black blood images by subtracting the MRA from the T1WI using the source image of PCA. We evaluated the motion artifact, detectability of clot, and precision in location and range compared these to that of susceptibility vessel sign in T2*WI and measured contrast ration (CR) of clot between the cistern and brain tissue. Motion artifact was visually evaluated using a 3-point scale. Detectability and precision of the location and range of occlusion clots were assessed by comparison with findings from digital subtraction angiography (DSA). Gwet's AC₁ and kappa statistics were used to assess inter-observer agreement. [Results] DEPICT showed significant robustness for motion artifact compared with T2*WI (p = 0.0026, Wilcoxon signed-rank test). DEPICT showed 100% detectability for the clot. Further, DEPICT showed higher Gwet's AC₁ and kappa statistic values with DSA than T2*WI. CR demonstrated a positive value. [Conclusions] DEPICT technique based on 1-min PCA offers both MRA and black blood T1W images that can be used to accurately evaluate both location and range of the clot.

Absence of Susceptibility Vessel Sign in Patients With Malignancy-Related Acute Ischemic Stroke Treated With Mechanical Thrombectomy

Background and Purpose

Clots rich in platelets and fibrin retrieved from patients with acute ischemic stroke (AIS) have been shown to be independently associated with the absence of the susceptibility vessel sign (SVS) on MRI and active malignancy. This study analyzed the association of SVS and the presence of active malignancy in patients with AIS who underwent mechanical thrombectomy (MT).

Methods

This single-center, retrospective, and cross-sectional study included consecutive patients with AIS with admission MRI treated with MT between January 2010 and December 2018. SVS status was evaluated on susceptibility-weighted imaging. Adjusted odds ratios (aORs) were calculated to determine the association between absent SVS and the presence of active or occult malignancy. The performance of predictive models incorporating and excluding SVS status was compared using areas under the receiver operating characteristics curve (auROC).

Results

Of 577 patients with AIS with assessable SVS status, 40 (6.9%) had a documented active malignancy and 72 (12.5%) showed no SVS. The absence of SVS was associated with active malignancy (aOR 4.85, 95% CI 1.94–12.11) or occult malignancy (aOR 11.42, 95% CI 2.36–55.20). The auROC of predictive models, including demographics and common malignancy biomarkers, was higher but not significant (0.85 vs. 0.81, p = 0.07) when SVS status was included.

Conclusion

Absence of SVS on admission MRI of patients with AIS undergoing MT is associated with malignancy, regardless of whether known or occult. Therefore, the SVS might be helpful in detecting paraneoplastic coagulation disorders and occult malignancy in patients with AIS.

Simultaneous feedback control for joint field and motion correction in brain MRI

T2*-weighted gradient-echo sequences count among the most widely used techniques in neuroimaging and offer rich magnitude and phase contrast. The susceptibility effects underlying this contrast scale with B₀, making T2*-weighted imaging particularly interesting at high field. High field also benefits baseline sensitivity and thus facilitates high-resolution studies. However, enhanced susceptibility effects and high target resolution come with inherent challenges. Relying on long echo times, T2*-weighted imaging not only benefits from enhanced local susceptibility effects but also suffers from increased field fluctuations due to moving body parts and breathing. High resolution, in turn, renders neuroimaging particularly vulnerable to motion of the head. This work reports the implementation and characterization of a system that aims to jointly address these issues. It is based on the simultaneous operation of two control loops, one for field stabilization and one for motion correction. The key challenge with this approach is that the two loops both operate on the magnetic field in the imaging volume and are thus prone to mutual interference and potential instability. This issue is addressed at the levels of sensing, timing, and control parameters. Performance assessment shows the resulting system to be stable and exhibit adequate loop decoupling, precision, and bandwidth. Simultaneous field and motion control is then demonstrated in examples of T2*-weighted in vivo imaging at 7T.

Increased susceptibility of asymmetrically prominent cortical veins correlates with misery perfusion in patients with occlusion of the middle cerebral artery

OBJECTIVES

To evaluate tissue perfusion and venous susceptibility in ischaemic stroke patients as a means to predict clinical status and early prognosis.

METHODS

A retrospective study of 51 ischaemic stroke patients were enrolled in this study. Susceptibility, perfusion and National Institute of Health stroke scale (NIHSS) were compared between patients with and without asymmetrically prominent cortical veins (APCVs). The correlation between susceptibility, perfusion and NIHSS was performed.

RESULTS

Compared to patients without APCVs, the age of patients with APCVs was statistically older (p = 0.017). Patients with APCVs at discharge showed clinical deterioration in their NIHSS. Mean transit time (MTT), time to peak (TTP) and cerebral blood flow (CBF) in the stroke hemisphere were statistically delayed/decreased in patients with and without APCVs (all p < 0.05). In patients with APCVs, the changes in susceptibility positively correlated with increases in MTT and TTP (p < 0.05). Susceptibility and TTP positively correlated and CBF negatively correlated with NIHSS both at admission and discharge (p < 0.05).

CONCLUSIONS

Patients with APCVs have a tendency of deterioration. The presence of APCVs indicates the tissue has increased oxygen extraction fraction. Increased susceptibility from APCVs positively correlated with the delayed MTT and TTP, which reflects the clinical status at admission and predicts an early prognosis.

KEY POINTS

• Patients with and without APCVs have similar misery perfusion. • Patients with APCVs have a tendency of deterioration compared to those without. • The presence of APCVs indicated the tissue has increased oxygen extraction fraction. • Increased susceptibility from APCVs positively correlated with the MTT and TTP. • Increased susceptibility from APCVs reflected the clinical status at admission.