EVALUATION OF SPECIFIC ABSORPTION RATE AMONG PATIENTS USING 3 TESLA AND 1.5 TESLA MAGNETIC RESONANCE IMAGING MACHINES

Abstract

Background: Specific Absorption Rate (SAR) is radiofrequency power delivered to tissue duringa Magnetic Resonance Imaging (MRI) examination, expressed as watts per kg (W/kg). Radiofrequencypower deposition results in increased heating of patient tissues; thus, the use of MRI has to becontrolled to ensure patient safety. Objective: The study aimed to evaluate SAR among patients using the 3 Tesla MRI (MRI 3T) and 1.5Tesla MRI (MRI 1.5T) machines. Methods: Data were obtained from patients who were examined using MRI 3T (1,159 patients, 8,225series) and MRI 1.5T (1,423 patients, 8,605 series) machines. Age, body weight, SAR, repetition time(TR), type of radiofrequency (RF) pulse and anatomical region exposed were studied. Results: Average SAR for all patients using the MRI 3T was lower than that of the MR 1.5T in everypart (p <0.001) = 0.92 ± 0.57 W/Kg, 2.45 ± 1.01 W/Kg, accordingly. The SAR that the patients receivedusing the spin echo technique revealed that T2 weighted image had lower SAR than T1 weighted imagefrom both MRI 3T and MRI 1.5T (p < 0.001), 0.87 and 0.98 W/kg for MRI 3T, 2.20 and 2.83 W/kg forMRI 1.5T, respectively. For underweight patients, the lowest SAR was 0.89 W/Kg (MRI 3T) and 2.40W/Kg (MRI 1.5T), respectively. Whereas, among overweight patients, the SAR was the highest at 0.97W/Kg (MRI 3T) and 2.52 W/Kg (MRI 1.5T). For SAR categorized by the flip angle of the RF pulse,and patients evaluated by the MRI 3T, the study revealed that the group with the flip angle of the RFpulse <75 degrees had lower SAR than the flip angle of the RF pulse >75 degrees, 0.77 W/Kg and 0.94W/Kg, accordingly (p < 0.001) similar to the MRI 1.5T. Conclusion: The average SAR of patients evaluated using the MRI 3T was lower than those of patientsevaluated using the MRI 1.5T in every body part examined. SAR was lower when the TR was increasedand flip angle was decreased.