Inter-observer variation and diagnostic efficacy of apparent diffusion coefficient (ADC) measurements obtained by diffusion-weighted imaging (DWI) in small renal masses.
BACKGROUND
Diffusion-weighted imaging (DWI) is increasingly used to diagnose renal lesion subtypes. Especially in small renal masses, identification of less aggressive tumor types is of clinical interest, as active surveillance strategies can be applied.


OBJECTIVE
To evaluate the inter-observer variation and diagnostic efficacy of apparent diffusion coefficient (ADC) measurements obtained by DWI in small renal masses ≤4 cm (SRM).


METHODS
This retrospective IRB-approved study included 39 patients (46 SRM: 12 benign, 34 malignant). All underwent a 3 T DWI of SRM prior to surgery. Two radiologists independently analyzed all imaging data by three measurements. Limits of agreement, intraclass correlation coefficients (ICC), group comparisons by t-tests, and ROC analysis were performed.


RESULTS
Reliability of ADC measurements was very high with an ICC of >0.9 for both observers. Inter-rater reliability was high with an ICC of 0.82. Limits of agreement for average ADC values between both observers were -23.5% to 38.3% with a mean difference of 7.5% between both observers. No significant differences were found between benign and malignant lesions (P value Observer 1: 0.362, Observer 2: 0.622). Papillary carcinoma showed lower ADC values compared to non-papillary carcinoma (P value Observer 1: 0.008, Observer 2: 0.012). Consequently, ROC analysis revealed a significant (P < 0.001, respectively) area under the ROC curve of 0.853 (Observer 1) and 0.837 (Observer 2) without significant differences between both readers (P = 0.772).


CONCLUSIONS
ADC measurements of SRM at 3 T show a high reproducibility and differentiate papillary from non-papillary carcinoma subtypes. However, measurement variability may limit the application of fixed ADC thresholds for lesion diagnosis.
Department of Radiology, University Hospital of Sankt-Pölten, St. Pölten, Austria.
Lothar
L
Ponhold
Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria.
Domagoj
D
Javor
Department of Radiology, University Hospital of Sankt-Pölten, St. Pölten, Austria.
Gertraud
G
Heinz-Peer
Department of Urology, Medical University of Vienna, Vienna, Austria.
Sabina
S
Sevcenco
Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria.
Martin
M
Hofstetter
Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria pascal.baltzer@meduniwien.ac.at.
Pascal Andreas
PA
Baltzer
D000368:Aged; D000369:Aged, 80 and over; D003287:Contrast Media; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007680:Kidney Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D015203:Reproducibility of Results
D003287:Contrast Media
Bland-Altman-plot; Diffusion-weighted imaging (DWI); ROC analysis; apparent diffusion coefficient (ADC); reproducibility; small renal masses