A Method for Evaluating the T2∗-weighting Effect in MRI

• Published in: Japanese Journal of Radiological Technology Vol. 78; no. 4; pp. 357 - 363
• Main Authors: Saito, Hiroaki, Ohkubo, Masaki, Yagi, Yuta, Kanazawa, Tsutomu
• Format: Journal Article
• Language: Japanese
• Published: Kyoto Japanese Society of Radiological Technology 01.01.2022; Japan Science and Technology Agency
• Subjects: Contrast agents; Image acquisition; Image contrast; Iron oxides; Magnetic resonance imaging; magnetic resonance imaging (MRI); Medical imaging; Parameters; Scanners; Simulation; superparamagnetic iron oxide (SPIO); susceptibility effect; T2-weighted image; Weighting
• ISSN: 0369-4305; 1881-4883
• DOI: 10.6009/jjrt.2022-1189

Purpose: To propose a method for evaluating the T2*-weighting effect in MRI. Methods: Multiple solutions with different concentrations of a superparamagnetic iron oxide contrast agent were made and their signal intensities on T2*-weighted images were measured. The relationship between iron concentration and signal intensity was determined, and we simulated an iron concentration map representing a simplified model of a brain microbleed and converted the pixel values in the map to signal intensity based on the determined relationship, generating a simulated T2*-weighted image. An ‘S-value’ parameter was defined to evaluate the low-intensity regions in the simulated image. S-values were obtained using T2*-weighted sequences acquired with different echo time (TE) values on three MRI scanners (Philips 1.5 T, GE 3.0 T, and Siemens 3.0 T). Another parameter (A-value) defined by the American Society for Testing and Materials (ASTM-F2119) for assessing artifacts was applied to evaluate the weighting effect in the T2*-weighted image of a laboratory-made susceptibility-effect phantom. Results: With all three scanners, the S-values increased as the TE increased, indicating enhancement of the T2*-weighting effect. For every TE, the S-values obtained for the Philips scanner were the largest, followed by those for the GE and Siemens scanners. The results of this comparative evaluation were similar to those obtained using A-values. Conclusion: Comparisons with the established A-value parameter showed our proposed method for the quantitative evaluation of the T2*-weighting effect using S-values to be valid. The proposed method has the advantage that the S-values do not depend on a specific susceptibility-effect phantom.