Yelong Shen1, Bin Zhao1, Guangbin Wang1, Shuang Yang1, Shan Li2, Josef Pfeuffer3, and Tianyi Qian4
1Shandong Medical Imaging Research Institute, School of Medicine, Jinan, China, People's Republic of, 2Department of Neurology, Provincial Hospital Affiliated to Shandong University, Jinan, China, People's Republic of, 3Siemens Healthcare, Application Development, Erlangen, Germany, Erlangen, Germany, 4Siemens Healthcare, MR Collaborations NE Asia, Beijing, China, People's Republic of
Synopsis
Single-TI
ASL usually underestimates the cerebral blood flow in areas with longer blood
arrival time, especially in the cerebellum. In this study, we built a template
of whole-brain cerebral blood flow and blood arrival time based on multi-inversion
time-ASL (mTI-ASL). No significant differences were found when comparing young
vs. old groups and female vs. male groups. The application in cerebellar
infarction patients demonstrates that mTI-ASL performs better than sTI-ASL
especially in areas with longer BAT. The CBF/BAT template created based on
normal subjects could be used to better identify perfusion deficits.PURPOSE:
Cerebral
blood perfusion can be measured by dynamic susceptibility contrast (DSC)
or arterial spin labeling (ASL). However, it is often difficult to visualize
bilateral low CBF using DSC, since it only provides semi-quantitative values, and
physician usually rely on the evaluation of interhemispheric differences to identify
abnormal perfusion patterns.
On
the other hand, single-TI ASL tends to underestimates the CBF in areas with
longer blood arrival time; especially in the cerebellum. In this study, we built
a template of whole-brain cerebral blood flow and bolus arrival time based on
multi-inversion time-ASL (mTI-ASL). The BAT/CBF template provides a standard
for diagnosing ischemia, and the diagnostic of patients with cerebellar infarction
or bilateral ischemic stroke could be facilitated by comparing the individual
perfusion maps to these templates.
METHODS:
49
healthy adults (25 males, age ranging from 25 to 50 with median of 36) and 8
patients with cerebellar infarction participated in this study. The MRI exam
consisted of Multi-TI ASL, T1 MPRAGE, T2-FLAIR and DWI. All data was collected
on a MAGNETOM Skyra 3T MR scanner (Siemens Healthcare, Erlangen, Germany). mTI-ASL
images were acquired with a prototype sequence with the following parameters:
TR/TE = 4600/22ms, FOV = 220 × 220mm
2, slice thickness = 4mm, voxel
size = 3.4 x 3.4 × 4.0mm
3, 36 slices, bolus length = 700ms, 16 TIs
from 480 to 4080ms, and total acquisition time = 5:09 min including an M0 scan.
The CBF/BAT/error maps were calculated inline on the scanner. MPRAGE was
acquired in sagittal orientation with 1 mm isotropic resolution (FOV = 230 ×
230 mm, 192 slices, TR/TE = 1900ms/2.58ms, TI = 900ms, flip angle = 9°) in 4:59
min. Voxels’ CBF/BAT values, which errors were larger than threshold during
curve fitting, was set to 0. The corrected CBF/BAT maps were first
co-registered to the subject’s individual MPRAGE images and then normalized to
the Montreal Neurological Institute (MNI) MNI152 T1 template. The normalized
CBF/BAT maps in MNI coordinate system were averaged among all healthy subjects
to create the normal CBF/BAT template.
The
CBF and BAT values of different brain areas were measured on the template using
manually drawn ROI. A voxel-based analysis was used to analyze the age (younger
group, 14 volunteers from 23 to 26 years old; older group, 14 volunteers from
30 to 58 years old) and gender effects (female group, 14 volunteers from 23 to
53 years old, average 32 years old; male group, 12 volunteers from 24 to 57
years old, average 31.5 years old). The CBF and BAT of the cerebellar infarction
patients were then compared with the template. The CBF obtained with single-TI
ASL (sTI-ASL) protocol (TI=2000ms) were also compared to mTI-ASL in both health
and patient group.
RESULTS:
The
mean CBF and BAT values of the different blood flow areas are shown in Figs. 2
and 3, respectively. The quantitative CBF values in different areas are consistent
with the results obtained with PET
1. The posterior circulation
territory has a longer BAT than the hemicerebrum. No significant differences were
found when comparing young vs. old groups and female vs. male groups. Fig. 4 shows
a decrease in CBF and increase in BAT over the lesion area (shown on T2-FLAIR),
compared to the template. On the opposite side of the lesion, CBF and BAT were still
in the same range as in normal subjects. Compared to CBF measured by mTI-ASL,
CBF obtained by using sTI-ASL shows significantly smaller values in both healthy
subjects (p<0.001) and patient (p<0.001) group.
DISCUSSION:
This
study indicates that CBF and BAT of different blood flow areas are not uniform,
so the sTI-ASL protocols cannot accurately estimate CBF for the whole brain,
especially for areas (such as the posterior circulation territory) with longer BAT
values. In this right-handed population, the left hemisphere has higher CBF
than the right hemisphere,and BAT of the left hemisphere is shorter than of the
right hemisphere. We did not find any differences between different age and
gender groups, so one standard template might be fit for evaluating CBF and BAT
changes in patients.
CONCLUSION:
The
mTI-ASL method could quantify CBF and BAT values of the whole brain in one
exam. It showed better performance than sTI-ASL, especially in areas characterized
by longer BAT. The normal-subject CBF/BAT template could be used to aid the
identification of perfusion deficits.
Acknowledgements
This work was funded in part by the Key R&D program in Shandong Province. The support of doctors (Fei Gao, Cuiyan Wang) and students (Junli Wang, Bao Wang) is gratefully acknowledged. References
[1]
P. van Gelderen et al. Pittfalls of MRI Measurement of White Matter Perfusion
Based on Arterial Spin Labeling. Magnetic Resonance in Medicine 59:788–795
(2008).