Paradoxical signal pattern of mediastinal cysts on T2-weighted MR imaging: phantom and clinical study.
OBJECTIVE
To evaluate the intracystic MRI (magnetic resonance imaging) signal intensity of mediastinal cystic masses on T2-weighted images.


METHODS
A phantom study was performed to evaluate the signal intensity of a mediastinal cystic mass phantom (rubber balloon containing water) adjacent to a cardiac phantom pulsing at the rate of 60/min. T2-weighted images (sequence, fast spin echo [FSE] and single shot fast spin echo [SSFSE]) were acquired for the mediastinal cystic mass phantom. Further, a clinical study was performed in 33 patients (16 men, 17 women; age range, 19-85 years; mean, 65 years) with thymic cysts or pericardial cysts. In all patients, T2-weighted images (FSE and SSFSE) were acquired. The signal intensity of cystic lesion was evaluated and was compared with that of muscle. A region of interest (ROI) was positioned on the standard MR console, and signal intensity of the cystic mass (cSI), that of the muscle (mSI), and the rate of absolute value of cSI-mSI to standard deviation (SD) of background noise (|cSI-mSI|/SD=CNR [contrast-to-noise ratio]) were measured.


RESULTS
The phantom study demonstrated that the rate phantom-ROI/saline-ROI was higher in SSFSE (0.36) than in FSE (0.19). In clinical cases, the degree of the signal intensity was higher in SSFSE than in FSE. The CNR was significantly higher in SSFSE (mean ± standard deviation, 111.0 ± 47.6) than in FSE (72.8 ± 36.6) (p<0.001, Wilcoxon signed-rank test).


CONCLUSIONS
Anterior mediastinal cysts often show lower signal intensity than the original signal intensity of water on T2-weighted images. SSFSE sequence reduces this paradoxical signal pattern on T2-weighted images, which may otherwise cause misinterpretation when assessing cystic lesions.
Department of Radiology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita-city, Osaka 565-0871, Japan. Electronic address: k-ueda@radiol.med.osaka-u.ac.jp.
Ken
K
Ueda
Department of Radiology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita-city, Osaka 565-0871, Japan.
Masahiro
M
Yanagawa
Department of Medical Physics and Engineering, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita-city, Osaka 565-0871, Japan.
Takashi
T
Ueguchi
Department of Radiology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita-city, Osaka 565-0871, Japan.
Yukihisa
Y
Satoh
Department of Radiology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita-city, Osaka 565-0871, Japan.
Misa
M
Kawai
Department of Radiology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita-city, Osaka 565-0871, Japan.
Tomoko
T
Gyobu
Department of Radiology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita-city, Osaka 565-0871, Japan.
Hiromitsu
H
Sumikawa
Department of Radiology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita-city, Osaka 565-0871, Japan.
Osamu
O
Honda
Department of Radiology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita-city, Osaka 565-0871, Japan.
Noriyuki
N
Tomiyama
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D008297:Male; D008476:Mediastinal Cyst / Q000473:pathology*; D008875:Middle Aged; D015588:Observer Variation; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D055815:Young Adult
MRI (magnetic resonance imaging); mediastinal cyst fast spin echo (FSE); single shot fast spin echo (SSFSE)