Fat Signal Fraction Research Articles

Late bone marrow changes in Hodgkin's disease patients: a characterization with proton chemical shift imaging

Our aim was to measure, by quantitative chemical shift imaging (CSI), the late therapy-induced changes in bone marrow (BM) of Hodgkin's disease (HD) patients. Fifteen HD patients treated with radiotherapy alone and radiochemotherapy (age at treatment between 11 and 50 years; post-treatment interval between 11 and 50 years; post-treatment interval between 15 and 127 months; applied dose 25.5 to 50 Gy), were studied with a 1.5 T MR imager. For the fat-water separation in-phase and opposed-phase (SE 1200/22) images were generated according to the Dixon method, with a modified post-processing. Long-term fatty replacement was seen in the irradiated BM only. The radiation fields were visualized as areas of high signal intensity in the T1-weighted images. There was a marked increase of the relative fat signal fraction in quantitative CSI without time, dose and age dependent recovery within the investigated ranges.

Fatty Liver

In vitro animal and human models were used to evaluate the potential of chemical shift magnetic resonance imaging (MRI) for assessing fatty liver. Phantoms of varying fat content were created from mayonnaise-agar preparations. Fatty liver was induced in eight rats by feeding them ethanol for three to six weeks (36% of total calories), whereas eight control rats were fed a normal diet. T1-weighted in-phase and opposed-phase MR images were obtained of the phantoms animals, and 28 human subjects. Additional images obtained in animals included long TR images with in-phase and opposed-phase technique, and hybrid chemical shift water and fat suppression. The rats were killed and histologic status was graded blindly by a hepatopathologist as normal, mild, moderate, or severe fatty change, for correlation with MR grading. Quantitative analysis of MR images included fat signal fraction for animals, and relative signal decrease between in-phase and opposed-phase images for phantom and human data. Phantom in-phase signal increased linearly with respect to fat content, whereas opposed-phase signal decreased linearly. MRI and histologic grading of rat livers were highly correlated, especially when based on water suppression images (r = 0.91, P = .0001). Opposed-phase images were also highly correlated, while fat suppression images were less effective. There was no overlap between MR-derived fat fractions for control (2.6%-5.7%) versus ethanol-fed rats (7.7%-17.9%, P = .0002). Human liver considered to be fatty by visual inspection (n = 8) had higher relative signal decrease than nonfatty liver (n = 22) (P less than .001). Phantom, animal, and human data demonstrate that comparison of T1-weighted in-phase and opposed-phase images is both practical and sensitive in the detection and grading of fatty liver.

Systemic Bone Marrow Disorders

In a prospective clinical study, 26 patients (22 with malignant lymphoma and 4 with myelofibrosis) and 9 healthy volunteers were examined by conventional magnetic resonance and proton chemical shift imaging (CSI; modified Dixon method). On the basis of the CSI data, a quantitative evaluation of the relative fat and water signal fractions in regions of interest of the femur, pelvis, and spine was performed. In 16 of 17 patients with biopsy-proven bone marrow disorders, CSI revealed a significant reduction in the fat fraction of the bone marrow relative to that of normal volunteers. The visual assessment could detect only 14 of the 17 pathological cases.