ADC measurements at low and high b values: insight into normal brain structure with clinical DWI.
OBJECTIVE
To demonstrate drop in brain ADC measurements from low to high b values; to evaluate the structural information provided based on those changes; and to discuss the anatomical reasons for ADC differences.


METHODS
Four cerebral ROI (precuneus-PRC, hippocampus-HIP, and the genu-GCC and splenium-SCC of the corpus callosum-CC) were drawn for ADC measurements with low (1000) and high (3000) b-value DWI in 50 normal subjects. ANOVA and Bonferroni correction tested ADC differences between areas, between both hemispheres, between GCC and SCC, and between b-value related ADC drop within areas. Pearson test evaluated dependence of interhemispheric and intercallosum ADC measurements obtained with the same b-value, dependence between areas of intrazonal drop, and the interhemispheric and intercallosum dependence of intrazonal drop.


RESULTS
ADCs differed between areas (P<.0001). Interhemispheric ADC only differed in PRC with low b-value (P<.027). No HIP asymmetries occurred regardless the b-value. ADC drop within PRC and HIP was similar but differed (P<.0001) from ADC drop within both CC ROI. ADC drop was also different between GCC and SCC (P<.0001). In PRC and HIP, ADC showed a significant interhemispheric and intrazonal dependence (P<.0001). There was no GCC to SCC ADC dependence. Intrazonal dependence in the CC was only significant in the SCC (P<.001). Interhemispheric dependence of intrazonal drop was significant (PRC P=.007; HIP P<.0001) but failed to reach significance in the CC.


CONCLUSIONS
Low and high b-value measurements show different diffusion behaviours within different tissues, especially in a highly anisotropic structure as the corpus callosum. This fact can provide valuable information about brain structure and different diffusion compartments in clinical DWI.
García Santos
José María
JM
Area de Neurorradiología, Cabeza y Cuello, Servicio de Radiodiagnóstico, Hospital General Universitario Morales Meseguer, Murcia, Spain. josem.garcia11@carm.es
Ordóñez
Cristina
C
Torres del Río
Silvia
S
D000328:Adult; D000704:Analysis of Variance; D001921:Brain / Q000033:anatomy & histology*; D001931:Brain Mapping / Q000379:methods*; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies