ABSTRACT
Objective To investigate the value of MR imaging methods for the quantification of fat content in a customized lipid phantom at 3.0 T.Methods Eleven homogeneous fat-water phantoms (50 ml)with fat volume percentages from 0 to 100％ were constructed with reference to Bernard's methods.Fat tractions of the lipid phantom were acquired using water selective saturation (WS),fat selective saturation (FS),in-and out-of-phase imaging (IOP),iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) gradient echo imaging and IDEAL Quant imaging methods on a 3.0 T MRI system.For statistical comparisons,paired-sample t test,Pearson correlation test,and Bland-Ahman maps were applied.Results Evaluated fat fractions acquired by WS,IDEAL Gradient echo imaging and IDEAL Quant were (49.6±28.8)％,(46.0±28.4)％,(51.0±32.0)％,the result has no significant difference with the true fat contents(t values were-0.186,-2.218,2.713;P values were 0.856,0.051,0.055).Evaluated fat fractions acquired by FS,corrected algorithm and IOP were (64.2±26.7)％,(58.9±31.9)％ and (45.3±32.3)％,these three kinds of methods have significant difference with the true fat contents (t values were 5.168,4.273,-6.441;P＜0.01).All the chemical shift imaging methods correlated with the true phantom model fat fractions,r values were 0.977(FS),0.978 (corrected algorithm),0.982 (WS),0.99 8(IOP),0.993 (IDEAL Gradient echo imaging),0.999 (IDEAL Quant) (all P＜0.01).Each method's 95％ confidence interval of the mean difference acquired by Bland-Altman map was WS (-14.7％ to 13.8％),FS (-3.6％ to 32.0％),corrected algorithm (-4.6％ to 22.5％),IOP(-9.4％ to 0.0％),IDEAL gradient echo imaging (-15.9％ to 7.8％),IDEAL Quant(-2.0％ to 4.0％).IDEAL Quant had the best correlation and confidence with the true fat fraction.Conclusions Chemical shift imaging methods (IOP,IDEAL Gradient echo imaging,IDEAL Quant) can acquire more accurate fat quantification results than chemical saturation imaging methods (FS,Corrected algorithm,WS) in a customized lipid phantom at 3.0 T.IDEAL Quant can acquire the best fat quantification result compared with the other imaging methods.
ABSTRACT
Objective To investigate the imaging features of Ewing's sarcoma and primitive neuroectodermal tumor (ES and PNET) in sacrum.Methods Imaging data were retrospectively collected and reviewed in 17 patients with ES and PNET confirmed by pathology.X-ray was performed in all patients,CT scans in 13 patients,and MR scans in 10 patients.Results All lesions were detected solitary and lateral.X-ray and CT features were lytic bone destruction in 12 cases,2 of them with bone sclerosis; one patient showed diffuse sclerosis.Soft tissue mass in pelvic cavity can be seen in 11 cases,9 of them with adjacent large blood vessels invasive and 4 patients with sacroiliac joints invasive.On post-contrast images,mild enhancement was found in 8 cases,and 5 patients with marked enhancement.MR images showed intermediate signal intensity on T1WI in 8 cases and heterogeneous moderate to high signal intensity on T2WI/fat suppression in 10 cases.DWI showed high signal intensity in 4 cases.Unlike CT scan,contrastenhanced MR images showed significant enhancement in 7 cases.Conclusions Ewing's sarcoma and primitive neuroectodermal tumor (ES and PNET) in sacrum have some specific imaging features.Imaging examination could provide reliable evidence for clinical diagnosis.