Simultaneous perfusion and permeability assessments using multiband multi‐echo EPI (M2‐EPI) in brain tumors

Abstract

Purpose To study a multiband multi‐echo EPI (M2‐EPI) sequence for dynamic susceptibility contrast (DSC) perfusion imaging with leakage correction and vascular permeability measurements, and to evaluate the benefits of increased temporal resolution provided by this acquisition strategy on the accuracy of perfusion and permeability estimations. Methods A novel M2‐EPI sequence was developed, and a pharmacokinetic model accounting for contrast agent extravasation was used to produce perfusion maps and additional vascular permeability maps. The advantage of M2‐EPI for DSC perfusion imaging was demonstrated in vivo in 5 patients with brain tumors, and numerical simulations were performed to evaluate the advantage of improved temporal resolution afforded by the technique. Results In contrast to underestimations of cerebral blood volume (CBV) in tumors using the single‐echo acquisition strategy, M2‐EPI provided more plausible estimates of CBV. A quantitative evaluation showed higher estimated values of CBV and mean transit time in tumor tissues using M2‐EPI (CBV: 3.08 ± 0.78 mL/100 g versus 1.56 ± 1.38 mL/100 g [P = .006]; mean transit time: 4.94 ± 1.17 seconds versus 1.83 ± 2.06 seconds [P = 0.033]). Numerical simulations showed that higher temporal resolution provided by M2‐EPI was associated with more accurate estimates of cerebral blood flow, CBV, and permeability parameters. Conclusion The novel M2‐EPI acquisition strategy for DSC imaging facilitates leakage‐corrected perfusion measurements with additional permeability assessments and more accurate estimates of perfusion/permeability parameters, and may be used as a quantitative tool for the diagnosis, prognosis, and treatment monitoring of brain tumors.

Alterations in Functional Network Topology Within Normal Hemispheres Contralateral to Anterior Circulation Steno-Occlusive Disease: A Resting-State BOLD Study

“…Fifth, single-band single-echo EPI with relatively low temporal (TR = 2 s) and spatial (voxel size = 3.4 × 3.4 × 4 mm 3 ) resolution was employed for BOLD imaging in this study. A recently developed multi-band multi-echo EPI ( 47 ) can be used to increase temporal and/or spatial resolution ( 48 , 49 ) and functional contrast-to-noise ( 50 ), thereby improving measurement accuracy. Finally, with an assumption of temporal stationarity, functional connectivity was calculated across the whole scan duration, and the future study of resting-state functional networks in terms of temporal fluctuations among patients with stroke and cerebrovascular disease may offer further mechanistic insights into the nature of remote functional connectivity in such patients.…”

Vessel architecture imaging using multiband gradient-echo/spin-echo EPI

“…Generally, the MB technique has been widely applied in the field of MR perfusion. MB with multi-echo EPI (3 and 7 echoes, respectively) has been applied to assess perfusion and permeability [28] and in hyperpolarized 13 C spectroscopic imaging [29]. MB acquisition was also successfully applied in ASL [30].…”

MR multitasking‐based dynamic imaging for cerebrovascular evaluation (MT‐DICE): Simultaneous quantification of permeability and leakage‐insensitive perfusion by dynamic T1/T2* mapping

“…Despite these promising results, multi‐echo‐based methods continue to face several technical challenges. First, temporal resolution and/or spatial coverage are often sacrificed because of the longer readout time of multiple echoes 19 . However, high temporal resolution is crucial for accurate quantification of DCE‐ and DSC‐MR parameters 21 .…”

“…After eliminating the ‐leakage effects, the remaining ‐leakage effects, which typically lead to overestimations of perfusion parameters, can further be mitigated by adopting either gamma‐variate fitting or model‐based postprocessing approaches. 17 , 18 , 19 , 20 …”

“…First, temporal resolution and/or spatial coverage are often sacrificed because of the longer readout time of multiple echoes. 19 However, high temporal resolution is crucial for accurate quantification of DCE‐ and DSC‐MR parameters. 21 Second, most existing techniques linearly transform the dynamic changes in signal intensity to CA concentration for kinetic modeling.…”