Erschienen in:
01.08.2012 | Urogenital
Diagnostic value of ADC in patients with prostate cancer: influence of the choice of b values
verfasst von:
Gregor Thörmer, Josephin Otto, Martin Reiss-Zimmermann, Matthias Seiwerts, Michael Moche, Nikita Garnov, Toni Franz, Minh Do, Jens-Uwe Stolzenburg, Lars-Christian Horn, Thomas Kahn, Harald Busse
Erschienen in:
European Radiology
|
Ausgabe 8/2012
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Abstract
Objectives
To evaluate the influence of the choice of b values on the diagnostic value of the apparent diffusion coefficient (ADC) for detection and grading of prostate cancer (PCa).
Methods
Forty-one patients with biopsy-proven PCa underwent endorectal 3-T MRI before prostatectomy. Different combinations of b values (0–800 s/mm2) were used to calculate four representative ADC maps. Mean ADCs of tumours and non-malignant tissue were determined. Tumour appearance on different ADC maps was rated by three radiologists as good, fair or poor by assigning a visual score (VS) of 2, 1 or 0, respectively. Differences in the ADC values with the choice of b values were analysed using one-way ANOVA.
Results
Choice of b values had a highly (P < 0.001) significant influence on the absolute ADC in each tissue. Maps using b = [50, 800] and [0, 800] were rated best (VS = 1.6 ± 0.3) and second best (1.1 ± 0.3, P < 0.001), respectively. For low-grade carcinomas (Gleason score ≤ 6, 13/41 patients), only the former choice received scores better than fair (VS = 1.4 ± 0.3). Mean tumour ADCs showed significant negative correlation (Spearman’s ρ −0.38 to −0.46, P < 0.05) with Gleason score.
Conclusions
Absolute ADC values strongly depend on the choice of b values and therefore should be used with caution for diagnostic purposes. A minimum b value greater than zero is recommended for ADC calculation to improve the visual assessment of PCa in ADC maps.
Key Points
• Absolute ADC values are highly dependent on the choice of b values.
• Absolute ADC thresholds should be used carefully to predict tumour aggressiveness.
• Subjective ratings of ADC maps involving b = 0 s/mm
2
are poor to fair.
• Minimum b value greater than 0 s/mm
2
is recommended for ADC calculation.