Authors:
T. Maris1, E. Chryssou1, O. Papakonstantinou2, N. Papanikolaou3, P. Prassopoulos4, N. Gourtsoyiannis3; 1Iraklion/GR, 2Athens/GR, 3Heraklion/GR, 4Alexandroupolis/GR
DOI:
10.1594/ECR03/C-1075
Methods and Materials
PatientsMR imaging studies of 40 thalassemic patients (mean age 28.55.4, median age : 27.6 yrs) 15 HCV(+) patients (mean age : 35.6 6.7 yrs, median age : 34.2 yrs) and 10 normal sublects were retrospectively reviewed. All thalassemic patients received systematic red blood cell transfusions and subcutaneous chelation with desferroxamine. Total iron burden was assessed in all thalassemic patients by means of Serum Ferritin Concentration (SFC) levels (range :900-5335 ng/ml) whereas liver iron concentration was determined in liver biopsy specimens obtained utilizing Fine Needle Aspiration (FNA) techniques and atomic absorption spectrophotometry methods for a sample of 14 patients (range : 1.4 - 7.2 mg/gr liver liver weight). MR imaging: Imaging techniqueAll MR imaging examinations were performed in a 1-year period, on a 1.5 T MR imaging system (Magnetom Vision Plus, Siemens). Body coil was used in all examinations for both signal excitation and signal detection. Respiratory triggering was used in order to monitor patients breathing. The general qualitative routine MR imaging protocols for liver studies conformed standard multi-slice 2D breathhold GRadient Echo (GRE) FLASH and Turbo Spin Echo (TSE) sequences. (T1w FLASH (TR/TE/FA : 160/4.2ms/70o), PDw FLASH (TR/TE/FA : 160/4.2ms/20o), T2*w FLASH (TR/TE/FA : 160/15ms/20o), T2w TSE (TR/TE/FA : 8000/90ms/90o)).All quantitative protocols enrolled in this study were standard 2D single slice protocols. For the T1 calculation a breathhold single-slice-single-echo (Turbo FLASH) GRE sequence (TR/TE/TImin/TImax/FA : 11/4.2/10/5000ms/10o) was used repeatably for 16 times each time varying TI from 10 ms 5000 ms (
Fig.1, Fig.2). For T2 calculation a respiratory gated single-slice-16-echo (PHAPS) SE sequence (TR/TE1/TE16/FA 2000/22.5/360ms/90o) was used (Fig.3, Fig.4). For the T2* calculation a breathhold single-slice-double-echo spoiled GRE sequence (TR/TE1/TE2/FA : 160/2.7/5.3ms/25o) Simultaneously IN-phase OPposed-phase (SINOP) was used repeatably for 8 times. Additionally, when appropriate for a faster calculation of T2* a 2D breathhold single slice Multi Echo (16 echoes) GRadient Echo (MEGRE) sequence (TR/TE1/TE16/FA 120/2.7/37.65ms/25o) was utilized (Fig.5, Fig.6).Aqueous solutions of Gd-DTPA and agarose gels were used as external reference standards for comparissons (Fig.7). Image analysisT2 and T2* values were calculated utilizing a weighted linear regression fitting model on which data were weighted according to background image random noise. Firstly background and random noise figures were calculated from the base images of either the T2 or the T2* sequence (Fig.8). The weighted linear regression analysis algorithm is applied in order to weight the data prior to the fit (fig.9). Late echo signals (near background) do not contribute for the calculation of T2 and T2*. After the fit, T2 and T2* are calculated either by using Regions Of Interest (ROI's) (Fig.10) or by using calculated image maps (Fig.11).