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Keywords:
Breast, MR-Diffusion/Perfusion, MR, Comparative studies, Cancer
Authors:
M. Wielema, M. D. Dorrius, H. Dijkstra, E. Langius, M. Oudkerk, P. E. Sijens; Groningen/NL
DOI:
10.1594/ecr2017/C-2765
Methods and materials
Patient population: In this retrospective study 41 consecutive women (ages 22-75,
mean age 47) with 50 mass enhanced breast lesions (44 malignant and 6 benign),
with an area of ≥ 0.8 cm2 were included between November 2008 and February 2011.
Mean lesions size was 2.0 cm2 (0.8-8.9 cm2).
Lesions smaller than 0.8 cm2 and non-mass enhancement lesions were excluded to reduce partial volume effect.
Exclusion criteria were: Cystic lesions,
previous breast malignancy,
breast surgery or breast radiation.
Final diagnosis was acquired by mastectomy (24),
lumpectomy (16),
core needle biopsy (6) or follow-up MRI for at least 2 years (4).
Data acquisition: All MRI examinations were performed using a 1.5 Tesla (T) system (Magnetom Avanto,
Siemens Medical Solutions,
Erlangen,
Germany).
Patients were placed in prone position.
The MRI protocol consisted of transversal Dynamic Contrast Enhanced (DCE) T1-weighted,
DW-images with b-values of 0,
50,
200,
500,
800 and 1000 s/mm2 and pre-contrast ADC maps were automatically calculated from the b=0 and b=1000 s/mm2 DWI series by dedicated software (AEGIS,
Hologic,
Mariborough,
USA).
Data analysis: Three observers independently drew four types of ROIs: observer 1 was a medical student,
observer 2 was a resident radiology,
observer 3 was a radiologist with 6 years of experience in breast radiology.
Observer 1 chose the largest cross section MRI slice,
based on the lesion diameter on DCE-T1 (Figure 1).
All observers placed ROI1 as an oval shape on that same slice,
to encompass most of the lesion,
while staying within its borders on the subtracted DCE-T1 series,
and copied ROI1 to the DW images with b-values of 0 and 1000 s/mm2.
Only b-values 0 and 1000 s/mm2 were used because that b-value combination showed the best discrimination between malignant and benign in a previous meta-analysis on DWI breast lesion evaluation.
[5] ROIs 2,
3 and 4 with standard size and shape were positioned on b-values 0 and 1000 s/mm2 as well.
Possible position mismatch was corrected: DW images guided by their position (ROI2) or ADC outcome (ROI3,4) (Figure 2).
ROI2 was a standardized circle of 0.3 cm2 positioned in the middle of the lesion.
ROI3 and ROI4 were also circular with fixed areas of 0.3 cm2 and 0.6 cm2 respectively and positioned inside ROI1 such that the lowest mean ADC was obtained.
Statistical analysis: For statistical analysis IBM SPSS Statistics 22 was used.
The intra- and inter-observer variability were calculated using the Intraclass Correlation Coefficient (ICC).
Dual axis plot was made for ROI1,
to visualize the agreement of the size of ROI1.
Differences between the mean ADC values of benign and malignant breast lesions were tested for significance by a sample t test.
The mean ADC values were calculated by combining the results of all three observers,
whereby the first set of measurements by observer 1 was used.
The area under the curve (AUC) was calculated using receiver operating characteristic (ROC) analysis for the mean ADC values of all observers and each ROI.
P-value of less than 0.05 was considered to indicate statistically significant difference.