Preliminary Study on the MR Temperature Mapping using Center Array-Sequencing Phase Unwrapping Algorithm

PURPOSE: To investigate the feasibility and accuracy of Proton Resonance Frequency (PRF) shift based magnetic resonance (MR) temperature mapping utilizing the selfdeveloped center array-sequencing phase unwrapping (PU) method for non-invasive temperature monitoring. MATERIALS AND METHODS: The computer simulation was done on the PU algorithm for performance evaluation before further application to MR thermometry. The MR experiments were conducted in two approaches namely PU experiment, and temperature mapping experiment based on the PU technique with all the image postprocessing implemented in MATLAB. A 1.5T MR scanner employing a knee coil with T2* GRE (Gradient Recalled Echo) pulse sequence were used throughout the experiments. Various subjects such as water phantom, orange, and agarose gel phantom were used for the assessment of the self-developed PU algorithm. The MR temperature mapping experiment was initially attempted on the agarose gel phantom only with the application of a custom-made thermoregulating water pump as the heating source. Heat was generated to the phantom via hot water circulation whilst temperature variation was observed with T-type thermocouple. The PU program was implemented on the reconstructed wrapped phase images prior to map the temperature distribution of subjects. As the temperature change is directly proportional to the phase difference map, the absolute temperature could be estimated from the summation of the computed temperature difference with the measured ambient temperature of subjects. RESULTS: The PU technique successfully recovered and removed the phase wrapping artifacts on MR phase images with various subjects by producing a smooth and continuous phase map thus producing a more reliable temperature map. CONCLUSION: This work presented a rapid, and robust self-developed center arraysequencing PU algorithm feasible for the application of MR temperature mapping according to the PRF phase shift property.

Localization of Accessory Pathway by Phase Image Analysis in Patients with Wolff-Parkinson-White Syndrome

To localize bypass pathways, left and right ventricular regions were analyzed at rest by phase image analysis in 6 patients with Wolff-Parkinoson-White syndrome and 5 patients with concealed bypass pathway. These were compared with image findings in 12 normal subjects. In normal subjects, the earliest emptying occured in ventricular septal, apical and left basal segments. Mean difference between the earlist left and right ventricular phase angle was 2.3+/-5.6degrees in patients with normal conduction, -14.0+/-15.1degrees in patients with left bypass pathways, 15.0+/-0degrees in patients with right bypass pathways and -6.6+/-12.3degrees in patients with concealed bypass pathways. In patients with bypass pathways, there was complete agreement between phase and electrophysiologic maps, but incomplete agreement(4 of 6) between surface ECGs and electrophysiologic map in a patient with left posterior and left bypass pathways. The phase image represents a new, noninvasive method of evaluating ventricular pre-excitation. The method may provide useful information complementary to that of electrocardiographic and electriphysiologic analysis.

The Usefulness of Color-Coded Phase Image for the Evaluation of Regional Wall Motion Abnormalities in Coronary Artery Disease

Phase and Amplitude Image were developed to overcome the subjective nature of interpretation for cinematic endless loop display of radionuclide gated blood pool scan. To evaluate the usefulness of color coded phase image in coronary artery disease, we conducted a clinical study with coronary angiography and phase image in 23 patients, and compared the results of those studies. 1) The results of coronary angiography revealed normal coronary artery in 6, 1 vessel disease in 11, 2 vessel disease in 4, and 3 vessel disease in 2 patients. 2) Color-coded Phase Image revealed abnormal phase area in 2/2(100%) of 3 vessel disease patients and in 3/4(75%) of 2 vessel disease patients, in 5/11(45%) of 1 vessel disease patients, and only 1/6(16%) of normal coronary artery. 3) Among the patients who disclosed abnormal phase image, 5 patients of 2-or3-vessl disease revealed abnormal phase through whole left ventricular area, but 3 patients with right coronary artery lesion and 2 patients with left antrior descending artery lesion showed localized abnormal phase area, infero-apical and anterior portion respectively, which were in accord with each coronary lesion. We concluded that the phase image may be useful in evaluation of the regional wall motion abnormalities in the patients of coronary artery disease. Further studies seem to be neccessary to clarify the sensitivity and specificity of the phase image in the each disease entity group.