title: Relative apparent diffusion coefficient: determination of reference site and validation of benefit for detecting metastatic lymph nodes in uterine cervical cancer.
abstract: OBJECTIVE
  To determine the reference site for relative apparent diffusion coefficient (rADC) and to evaluate the benefit of rADC for detecting metastatic lymph nodes in uterine cervical cancer.
  
  
  METHODS
  Two observers independently measured ADCs in the spleen, liver, renal cortex, lumbar spine, lumbar spinal cord, and gluteus maximus on diffusion-weighted images (b value, 0 and 1000 mm/sec(2)) in 50 patients. The reference site for rADC was determined using the intra- and interobserver coefficient of variation (CV) of ADC in these organs. rADC was calculated by ADC(lesion)/ADC(reference site). The benefit of rADC over ADC was validated by comparing the area under the receiver operating curve for identifying metastatic lymph nodes in uterine cervical cancer in 130 patients.
  
  
  RESULTS
  The renal cortex was determined to be the reference site for rADC, as its CVs (intraobserver, 5%-7%; interobserver, 5%) were less than those of the other organs (P < 0.05). The ADC and rADC of metastatic lymph nodes (n = 29, ADC, 0.7483 x 10(-3) mm(2)/sec; rADC, 0.3832) were less than those of nonmetastatic lymph nodes (n = 229, ADC, 0.9960 x 10(-3) mm(2)/sec; rADC, 0.5383) (P < 0.05). The area under the receiver operating characteristics curve for differentiating metastatic from nonmetastatic lymph nodes was greater for rADC (0.914; 95% confidence interval [CI], 0.872-0.945) than for ADC (0.872; 95% CI, 0.825-0.910) (P = 0.007).
  
  
  CONCLUSIONS
  The renal cortex is an appropriate reference site for rADC and rADC may improve the accuracy for diagnosing metastatic lymph nodes in uterine cervical cancer.
authors.affiliation: Department of Radiology, University of Ulsan, Seoul, South Korea.
authors.forename: Sang Ok
authors.initials: SO
authors.lastname: Park
authors.forename: Jeong Kon
authors.initials: JK
authors.lastname: Kim
authors.forename: Kyoung Ah
authors.initials: KA
authors.lastname: Kim
authors.forename: Bum-Woo
authors.initials: BW
authors.lastname: Park
authors.forename: Namkug
authors.initials: N
authors.lastname: Kim
authors.forename: Gyunggoo
authors.initials: G
authors.lastname: Cho
authors.forename: Hyuk Jae
authors.initials: HJ
authors.lastname: Choi
authors.forename: Kyoung-Sik
authors.initials: KS
authors.lastname: Cho
mesh_terms: D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D007672:Kidney Cortex / Q000033:anatomy & histology; D008198:Lymph Nodes / Q000473:pathology*; D008207:Lymphatic Metastasis; D008875:Middle Aged; D012372:ROC Curve; D015203:Reproducibility of Results; D012189:Retrospective Studies; D014594:Uterine Neoplasms / Q000473:pathology*