This study aims to observe and estimate the temperature changes caused by the echo train lengths (ETLs) of
fast-spin echo to ensure radiofrequency (RF)-related safety. RF-induced heating on ETL-stepped changes is
evaluated using the proton resonance frequency shift (PRF) method and optic-fiber thermography (OFT). The
increase in temperature caused by a clinical sequence was compared to that accumulated by the corresponding
ETLs. The temperatures are similarly increased in ETLs from 10 to 30 (PRF: 0.109 ± 0.025 ^oC, OFT: 0.079 ±
0.009 ^oC), suggesting that a large number of ETLs could be utilized at practical sites. The RF-induced heating
in the clinical setting (PRF: 0.775 ± 0.069 ^oC, OFT: 0.510 ± 0.015 ^oC) is comparable to the estimated temperature
on the ETL-stepped changes (PRF: 0.780 ^oC, OFT: 0.553 ^oC). These enable accelerated acquisition with a
large number of ETLs to be practically used and RF-induced safety to be thoroughly guaranteed.