[MRI diagnosis of the lung nodule--experimental and clinical studies regarding environmental effects on relaxation time measurement].

There have been several reports on MRI concerning the differential diagnosis of lung nodules by the measurement of relaxation time. Measuring the relaxation time has been reported to be of little value because of a lack of reliability in differentiating nodules, and may vary according to environmental effects such as tumor size, location and physical constitution as seen on CT. From this point of view, we have newly devised a phantom of the thorax containing simulated lung nodules in order to evaluate the environmental effects on the relaxation time, and investigated the fluctuation of the T1 and T2 values of lung nodules of the phantom. The experimental study using simulated lung nodules revealed that T1 and T2 values of the lung nodules shift according to various environmental factors such as tumor size, location, and blood flow. It is concluded that there are definite environmental effects on MRI measurements as seen on CT. In clinical studies with patients showing nodular shadows on chest radiography, we calculated the T1 and T2 relaxation times of lung nodules pre- and post-operatively. The T1 and T2 relaxation times of resected tumors were measured approximately 2 hours after surgery. There was a tendency for the T1 values to decrease and T2 values to increase when compared to preoperative conditions. However it could not be proved that the changes of the relaxation times were solely due to environmental effects, because there were lots of valid causes which affect remained such as loss of blood flow and tissue degeneration after surgery.