Time Resolution Improvement of MRI Temperature Monitoring Using Keyhole Method

PURPOSE: This study proposes the keyhole method in order to improve the time resolution of the proton resonance frequency(PRF) MR temperature monitoring technique. The values of Root Mean Square (RMS) error of measured temperature value and Signal-to-Noise Ratio(SNR) obtained from the keyhole and full phase encoded temperature images were compared. MATERIALS AND METHODS: The PRF method combined with GRE sequence was used to get MR temperature images using a clinical 1.5T MR scanner. It was conducted on the tissue-mimic 2% agarose gel phantom and swine's hock tissue. A MR compatible coaxial slot antenna driven by microwave power generator at 2.45GHz was used to heat the object in the magnetic bore for 5 minutes followed by a sequential acquisition of MR raw data during 10 minutes of cooling period. The acquired raw data were transferred to PC after then the keyhole images were reconstructed by taking the central part of K-space data with 128, 64, 32 and 16 phase encoding lines while the remaining peripheral parts were taken from the 1st reference raw data. The RMS errors were compared with the 256 full encoded self-reference temperature image while the SNR values were compared with the zero filling images. RESULTS: As phase encoding number at the center part on the keyhole temperature images decreased to 128, 64, 32 and 16, the RMS errors of the measured temperature increased to 0.538, 0.712, 0.768 and 0.845degrees C, meanwhile SNR values were maintained as the phase encoding number of keyhole part is reduced. CONCLUSION: This study shows that the keyhole technique is successfully applied to temperature monitoring procedure to increases the temporal resolution by standardizing the matrix size, thus maintained the SNR values. In future, it is expected to implement the MR real time thermal imaging using keyhole method which is able to reduce the scan time with minimal thermal variations.

Quality of Life after Total Knee and Total Hip Replacement

We reviewed 40 consecutive patients having a primary total hip replacement(THR) and 60 patients having a primary total knee replacement(TKR) for osteoarthritis to compare the qu;dity of hfe(QoL) before and after operation. Bilateral arthroplasties were perfomed 10 cases of THR and 25 cemes of TKR. We used a modified Harris hip score and a knee score of American knee society, the Rosser Lndex Matrix and authors eval- uation system to generate these scores. Quality of life was highly improved by Rossers and authors evalua- tion system after THR and TKR. The median values of QoL scores before and after operation were signifi- cantly different(petter than in TKR. Postoperative QoL scores for both groups were similar. Quality of life evaluated by Rossers score and authors evaluation system in bilateral THR was better than bilateral TKR. We think better quality of life in bilateral THR over bilateral TKR by authors evaluation system is because the hip joint is mcire stable and has better range of motion than knee joint. We conclude that change of life style including the use of bed, toilet seat elevation, and the use of dinning table will be neccesary after bilateral TKR.