Detection of small metastatic brain tumors: comparison of 3D contrast-enhanced whole brain-black blood imaging and MP-RAGE imaging

Keywords: brain metastasis, gamma knife, Imaging, radiosurgery, magnetic resonance imaging

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     Early and accurate diagnosis of small metastatic brain tumors may affect outcomes as well as treatment strategies. For this reason, 3D thin-section imaging is preferred. However, at conventional contrast-enhanced(CE) 3D imaging such as magnetization prepared rapid gradient echo(MP-RAGE), many visually enhanced vessels may mimic small metastatic tumors, hindering tumor detection. We developed CE black-blood single-slab 3D turbo-spin echo imaging(BB-ssTSE), which employs variable refocusing flip angles and flow-sensitizing gradient schemes, to enhance metastatic brain tumors while selectively suppressing blood vessels. 
     The purpose of this work was to investigate the efficiency of the proposed CE BB-ssTSE in detecting small metastatic brain tumors as compared to conventional MP-RAGE.
     The combined evaluation of MP-RAGE+BB-ssTSE showed 242 tumors in 28 patients.
     Numerical comparisons of MP-RAGE and BB-ssTSE were performed by simulation studies to investigate the signal/contrast behaviors of flowing blood and stationary CE tumors. For in vivo studies, we enrolled 35 patients with breast or lung cancer who underwent brain MRI. After administering a double dose of contrast medium, whole brain 2D T1-weighted imaging followed by high resolution isotropic 3D BB-ssTSE and MP-RAGE was performed at 3T. Two reviewers independently evaluated the presence of metastatic brain tumors using: 1) MP-RAGE; 2) BB-ssTSE; and 3) MP-RAGE+BB-ssTSE sequentially. Another reviewer compared the detection rates of metastatic brain tumors between BB-ssTSE and MP-RAGE.
     Numerical simulations showed that the proposed BB-ssTSE effectively attenuated the signal intensity of flowing blood over the entire echo train, resulting in CE tumor-to-white matter contrast comparable to conventional MP-RAGE.  Of these 242 tumors, 153 lesions were less than 5mm. MP-RAGE found 111 small metastatic brain tumors, BB-ssTSE found 150, and MP-RAGE+BB-ssTSE found 153. Significantly more small tumors were detected by BB-ssTSE than MP-RAGE(P=0.001, Wilcoxon signed-rank test). All large tumors were detected similarly by both MP-RAGE and BB-ssTSE. By combined results for MP-RAGE+BB-ssTSE, sensitivities for detection of small metastatic tumors were 72.5% for MP-RAGE and 98.0% for BB-ssTSE(P<0.0001, McNemar test).
     This was a retrospective analysis.
     Compared with conventional MP-RAGE, the proposed CE BB-ssTSE imaging, which enhances tumors while selectively suppressing blood vessels, leads to significantly better detection of small metastatic brain tumors less than 5mm.
     The accurate detection of small tumors may influence management.


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