title: Grading astrocytic tumors by using apparent diffusion coefficient parameters: superiority of a one- versus two-parameter pilot method.
abstract: OBJECTIVE
  To assess the utility of both minimum apparent diffusion coefficients (ADCs) and ADC difference values for grading astrocytic tumors at magnetic resonance imaging.
  
  
  METHODS
  The hospital's institutional review board approved this retrospective study and waived informed consent. Fifty patients (23 male patients, 27 female patients; median age, 53 years) with newly diagnosed astrocytic tumors were evaluated. Two observers blinded to clinical information independently measured the ADCs by manually placing three to five regions of interest (40-60 mm(2)) within the solid tumor either with or without contrast material-enhanced components and calculated the average ADC. Minimum and maximum ADCs were selected, and the difference between them was recorded as the ADC difference value. These ADC values were used as the parameters for tumor grading and were compared by using the Kruskal-Wallis test and receiver operating characteristic (ROC) curve analysis.
  
  
  RESULTS
  According to ROC analyses for distinguishing tumor grade, minimum ADCs showed the largest areas under the ROC curve. Minimum ADCs optimally helped distinguish grade 1 from higher-grade tumors at a cutoff value of 1.47 x 10(-3) mm(2)/sec and grade 4 from lower-grade tumors at a cutoff value of 1.01 x 10(-3) mm(2)/sec (P < .001 for both). ADC difference values helped distinguish grade 2 from grade 3 tumors at a cutoff value of 0.31 x 10(-3) mm(2)/sec (P < .001). When tumors were graded by using the combined minimum ADC and ADC difference cutoff values mentioned above (the two-parameter method), the following positive predictive values were obtained: grade 1 tumors, 73% (eight of 11); grade 2 tumors, 100% (five of five); grade 3 tumors, 67% (eight of 12); and grade 4 tumors, 91% (20 of 22).
  
  
  CONCLUSIONS
  Using a combination of minimum ADCs and ADC difference values (the two-parameter method) facilitates the accurate grading of astrocytic tumors.
authors.affiliation: Department of Radiation Oncology, Kumamoto University Hospital, 1-1-1 Honjo, Kumamoto 860-8556, Japan. murakami@kumamoto-u.ac.jp
authors.forename: Ryuji
authors.initials: R
authors.lastname: Murakami
authors.forename: Toshinori
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authors.lastname: Hirai
authors.forename: Takeshi
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authors.lastname: Sugahara
authors.forename: Hirofumi
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authors.lastname: Fukuoka
authors.forename: Ryo
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authors.forename: Shinichiro
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authors.lastname: Nishimura
authors.forename: Mika
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authors.lastname: Kitajima
authors.forename: Tomoko
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authors.lastname: Okuda
authors.forename: Hideo
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authors.lastname: Nakamura
authors.forename: Natsuo
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authors.lastname: Oya
authors.forename: Jun-ichi
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authors.lastname: Kuratsu
authors.forename: Yasuyuki
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authors.lastname: Yamashita