Magnetization transfer imaging shows tissue abnormalities in the reversible penumbra.
OBJECTIVE
In the concept of ischemic penumbra, the volume of salvaged penumbra is considered as the volume of FLAIR normalization on follow-up MRI compared with early diffusion and perfusion abnormalities. Using magnetization transfer imaging, very sensitive to macromolecular disruption, we investigated whether FLAIR normalization was a good marker for tissue full recovery.


METHODS
We prospectively included 30 patients with acute middle cerebral artery stroke. Diffusion-weighted imaging (DWI) and perfusion-weighted imaging were performed within 12 hours after onset (MRI.1), and the final infarct was documented by MRI with FLAIR and magnetization transfer at 1-month follow-up (MRI.2). We compared magnetic transfer ratio of a normal region with values measured at 1 month (MRI.2) in 4 regions of interest: (1) the initial DWI hypersignal (CORE=DWI MRI.1); (2) the infarct growth area (infarct growth=FLAIR MRI.2-DWI MRI.1); (3) the hypoperfused area that normalized (reversible perfusion abnormalities=perfusion-weighted imaging MRI.1-FLAIR_ MRI.2); and (4) the early DWI abnormalities that normalized (reversible diffusion abnormalities=DWI MRI.1- FLAIR_MRI.2).


RESULTS
In comparison with values obtained in normal tissue (magnetic transfer ratio=49.8%, SD=1.9), magnetic transfer ratio at 1 month was significantly decreased in reversible perfusion abnormalities (45.2%, SD=2.5; P<0.0001) and reversible diffusion abnormalities (43.2%, SD=2.8; P=0.0156). It was also markedly reduced, as expected, in the CORE (40.9%, SD=5.2) and infarct growth regions (43.1%, SD=2.0).


CONCLUSIONS
Magnetic transfer ratio assessed presence of microstructural damages in the MRI-defined salvaged penumbra. This may imply cellular loss and partial infarction. Evaluation of the efficacy of therapies that promote reperfusion or neuroprotection may benefit from this additional information.
Tourdias
Thomas
T
CHU de Bordeaux, Université Victor Segalen Bordeaux 2, Service de Neuroradiologie diagnostique et thérapeutique, Place Amélie Raba-Léon, Bordeaux, France.
Dousset
Vincent
V
Sibon
Igor
I
Pele
Eric
E
Menegon
Patrice
P
Asselineau
Julien
J
Pachai
Chahin
C
Rouanet
François
F
Robinson
Philip
P
Chene
Geneviève
G
Orgogozo
Jean Marc
JM
D000208:Acute Disease; D000328:Adult; D000368:Aged; D002545:Brain Ischemia / Q000175:diagnosis* / Q000473:pathology; D002560:Cerebrovascular Circulation; D004058:Diffusion; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008280:Magnetics; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D009474:Neurons / Q000378:metabolism; D020521:Stroke / Q000175:diagnosis* / Q000473:pathology