Line Brennhaug Nilsen1, Knut Håkon Hole2, Ingrid Digernes1, Endre Grøvik3, Oliver Geier1, Edmund Reitan2, Cathrine Saxhaug4, Åslaug Helland4, Kari Dolven Jacobsen4, Birger Breivik5, Dag Ottar Sætre6, and Kyrre Eeg Emblem1
1Diagnostic Physics, Oslo University Hospital, Oslo, Norway, 2Radiology and Nuclear Medicine, Oslo University Hospital, Oslo, Norway, 3Diagnostic Physic, Oslo University Hospital, Oslo, Norway, 4Oslo University Hospital, Oslo, Norway, 5Hospital of Southern Norway, Kristiansand, Norway, 6The Hospital Østfold Kalnes, Kalnes, Norway
Synopsis
In this
study, we aimed to assess the potential of using intravoxel incoherent motion (IVIM)
for measuring cerebral blood volume (CBV) in brain metastases and normal brain
tissue. DWI was acquired with b=0, 200, 300 and 1000s/mm2 in nineteen
patients with 23 brain metastases from lung cancer. Asymptotic IVIM fitting
yielded an estimation of the perfusion fraction, and subsequent estimation of CBV.
CBVDWI in brain metastases and gray matter correlated significantly
with CBV obtained from conventional DSC MRI. Our results suggest that IVIM may serve
as an independent and reliable surrogate marker of blood volume in well
perfused brain tissue.
INTRODUCTION
Diffusion-weighted
Imaging (DWI) is a fast and easily accessible technique that has become an
essential part of oncological imaging protocols. An increasing number of
intracranial DWI studies, predominantly in glioblastoma and gliomas1,
have incorporated the intravoxel incoherent motion (IVIM) concept2,
and demonstrated its potential for providing parameters reflecting cerebral
blood volume (CBV) and perfusion without the use of intravenous contrast agent.
The original IVIM concept relies on bi-exponential DWI signal decay, and accurate
estimation of perfusion parameters requires image acquisition with a large
number of b values3. In our study, we used a simplified model with asymptotic
fitting, essentially requiring no more than three b values, to estimate
cerebral blood volume4, CBVDWI, in metastases from lung
cancer and normal brain tissue. The CBVDWI was compared with
conventional perfusion parameters obtained from Dynamic Susceptibility Contrast
(DSC) Magnetic Resonance Imaging (MRI).METHODS
Twenty-three
untreated brain metastases in 19 patients with primary non-small cell lung
cancer have been included in this prospective study so far. DWI and DSC MRI were
performed on a 3T scanner. DWI was acquired in three orthogonal directions with
four b values: 0, 200, 300 and 1000 s/mm2 (TR/TE=5960/71 ms, voxel size = 1.22 x
1.22 mm2). A single region of interest (ROI) was manually placed
separately on the DWI and DSC images in normal gray matter and white matter,
and within tumor tissue in the image slice showing the greatest extent of solid
tumor. The placement of ROIs was guided by co-registered high-resolution 3D
isotropic T1w post-contrast images. Median DWI signal intensity within each ROI
was used for estimation of the diffusion coefficient, Dlinear, and
the perfusion fraction, flinear, which was subsequently used for calculation
of CBVDWI as previously reported4. Post-processing of DSC
spin-echo data provided maps of CBVDSC and CBFDSC5.
Image analysis was performed in nordicICE and in the Interactive Data Language.RESULTS
Table 1 shows median values (range) of DWI and DSC
metrics from ROIs within metastases and normal brain tissue. Maps of these
metrics are shown in Fig. 1. Gray matter was characterized by higher blood
volume and blood flow than white matter (p<0.01). There was a strong
positive correlation between CBV
DWI and CBV
DSC (Fig. 2) in
metastases (Spearman’s ρ correlation; 0.739, p<0.01) and gray matter (Spearman’s ρ correlation; 0.633,
p < 0.01). No significant correlation was however found for these parameters
in white matter (Spearman’s ρ; 0.311). CBV
DWI correlated with CBF
DSC (Spearman’s ρ; 0.482,
p<0.05), but weaker than for CBV
DSC and CBF
DSC (Spearman’s ρ; 0.623,
p<0.05).
DISCUSSION AND CONCLUSION
In our study, we
show that asymptotic fitting of DWI signal decay in brain metastases from lung
cancer and normal gray matter yields an estimation of cerebral blood volume that
strongly correlates with blood volume obtained from conventional DSC MRI. The
lack of correlation between CBV
DWI and CBV
DSC in white
matter may be due to the inherently low blood volume of white matter.
Similarly, lower agreement between CBV
DWI and CBV
DSC is
seen in metastases with low cerebral blood volume. IVIM
may serve as an independent and reliable surrogate marker of blood volume in
well perfused brain tissue in the absence of contrast-enhanced MRI.
Acknowledgements
No acknowledgement found.References
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