DiSpect reveals modulation and redistribution of venous blood flow caused by neural activation

2436 

Abstract Submission 

Ekin Karasan¹, Chunlei Liu¹, Michael Lustig¹

¹Electrical Engineering and Computer Sciences, University of California, Berkeley, Berkeley, CA

Ekin Karasan  
Electrical Engineering and Computer Sciences, University of California, Berkeley
Berkeley, CA

Chunlei Liu  
Electrical Engineering and Computer Sciences, University of California, Berkeley
Berkeley, CA

Michael Lustig  
Electrical Engineering and Computer Sciences, University of California, Berkeley
Berkeley, CA

Functional MRI (fMRI) techniques probe the hemodynamic response resulting from neuronal activation. Among fMRI methods, blood-oxygenation-level-dependent (BOLD) contrast is most prominent[1,5,8]. One disadvantage is that BOLD is affected by the complex interplay of many processes[9-11], including blood oxygenation, cerebral blood volume (CBV) and cerebral blood flow (CBF). Vascular space occupancy[7] and Arterial Spin Labeling fMRI[2] are alternative methods that directly measure changes in a single process: CBV and arterial CBF, respectively.

We recently introduced Displacement Spectrum Imaging (DiSpect), which is a method based on spin position tagging and imaging[3,4,12]. Previously[4], we showed that DiSpect can trace blood flow from the capillary bed into the superior cerebral veins and map venous territories (Figure 1a). Here, we show that DiSpect can consistently detect alterations in local venous blood flow due to motor cortex activation (Figure 1b).

Pulse Sequence:

The full DiSpect acquisition (20-30 minutes) was split into 20-second partitions to keep task durations short (Figure 1c). Partitions were repeated during task and at baseline before moving to the next. Multi-Slice Spiral-BOLD acquisitions were performed between partitions to ensure that activation is consistently occurring throughout the scan. Partitions were combined to form task and baseline blood source maps.

Experiments:

Two subjects were scanned using a 3T GE MR750W (GE Healthcare; Waukesha, WI). The superior cerebral veins were imaged with 2D DiSpect acquisitions during task and baseline with an axial imaging slice as placed in Figure 1d (resolution=4x4mm²/FOV=16x16cm²). Displacement encoding (displacement resolution=8x8mm²/FOV=11.2x8cm²) was performed along the LR and SI directions, producing coronal blood source maps (projected along AP). Data was collected for evolution times between 100ms to 3s after tagging (150ms increments). For the task, Subject 1 was instructed to squeeze both hands while Subject 2 was instructed to squeeze only their right hand.

For each subject, a product 2D EPI-BOLD (res=3.3x3.3mm²/FOV=21x21cm²/TR=2s/TE=28ms) acquisition was performed. The subject was asked to perform the task for 20s on and 20s off for 5 minutes.

Quantitative Susceptibility Mapping (QSM) was used to obtain venous structure, with protocol in [4]. STI Suite V3.0[13] was used to produce susceptibility maps using the iLSQR[6] method. A maximum intensity projection was used to visualize coronal vein structure.

Data Analysis:

BOLD datasets were analyzed with SPM12[14]. T-statistic images were produced with a cluster significance threshold of p=0.01.

The percentage signal change in the blood source maps was determined as:
%Signal Change = (S_task -S_baseline)/S_baseline x 100%.

Results from Subject 1 with bilateral motor cortex activation and Subject 2 with unilateral left motor cortex activation are shown (Figure 2). Two veins are selected for each subject. For Subject 1, two (orange) veins drain the activated motor cortices. For Subject 2, one (orange) vein drains the activated left motor cortex and one (blue) is selected as control. The blood source maps and their percentage change is shown (Figure 2c).

In both subjects, the source maps of the activated veins show a large blood flow increase close to the BOLD activation. For Subject 1, a local decrease in blood flow is also observed in the right motor cortex, slightly further away from the neural activation, suggesting a possible redistribution of blood flow. The control vein for Subject 2 shows little percentage change.

DiSpect can capture venous blood flow changes during a motor cortex task. BOLD contrast is affected by a complex interplay of several physiological processes. DiSpect probes changes in venous blood flow and can help to better understand the venous contributions in the BOLD signal.

Non-BOLD fMRI ¹

Imaging Methods Other ²

Blood

Cerebral Blood Flow

fMRI CONTRAST MECHANISMS

FUNCTIONAL MRI

Motor

MRI