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Patient population:
Dynamic contrast-enhanced MRI with gadofosveset trisodium (Ablavar®,
Lantheus Medical Imaging,
Billerica,
MA,
North American and Australian rights) was used for research in rectal cancer.
Rectal cancer patients were retrospectively selected from a dataset of patients who had DCE-MRI for (re)staging which was approved by the local institutional review board.[15] For comparison of enhancement characteristics a small group of similar patients underwent DCE-MRI with gadobutrol (Gadovist®,
Schering AG,
Berlin,
Germany) with the same DCE-MRI protocol.
Contrast agents:
Gadobutrol has an intravascular half-life of 100seconds and a relaxivity of 5.2 L/mmol-1/s-1.[1,
2,
12] Gadofosveset trisodium is an intravascular blood pool agent with an intravascular half-life of circa 28 minutes and a relaxivity of 19 L/mmol-1/s-1due to the formation of albumin-GDF complexes.[12]
MRI sequences:
MRI examinations were performed at 1.5T (Intera or Ingenia,
Philips Medical Systems,
Best,
the Netherlands).
An intravenous bolus injection of 20mg butylscopolamine (Buscopan®,
Boehringer Ingelheim bv,
Ingelheim,
Germany) was the only administered bowel preparation.
DCE-MRI was performed with multiple flip angles (5,
10,
15,
20,
25) spoiled gradient echo sequences with identical TR and TE that were acquired with the same geometrical characteristics as the DCE-MRI sequence,
to calculate T1 relaxation times.
The DCE sequence was a transverse T1-weighted 3D fast field echo,
identically angled to the transverse T2-weighted sequence,
with 10mm thickness and overcontiguous slices.
Temporal resolution was 8s,
TR/TE 7.9/4.6ms,
30° flip angle,
11 slices,
5 mm slice thickness,
5 mm interslice distance.
Total acquisition time was 6 minutes.
In plane resolution was 0.43 mm x 0.34 mm,
matrix 512 x 512,
and FOV 220 mm x 220 mm.
No view sharing was used.
After 24s (three series) of unenhanced baseline measurements one of both contrast agents was injected (rate of 0.70ml/s for GDF and 2ml/s for GDB) into the brachial vein,
followed by a 20ml saline flush using an MR compatible power injector (Spectris Solaris,
MEDRAD,
Warrendale,
Pennsylvania,
USA).
Image analysis
Whole tumour regions of interest (ROIs) were delineated by an expert reader (MM,
with 8 years of experience in rectal cancer MRI)) on all slices with visible tumour.
ROIs were drawn on the DCE-images while the T2-weighted images were available to the reader for reference.
Drawing was performed in the IntelliSpace Discovery Platform (IntelliSpace Portal 7.0,
Philips Healthcare systems,
Aachen,
Germany).
Volumes of interest (VOIs) were then extracted by use of the ROIs as niftii file formats and used for semiquantitative analyses.
Semiquantitative analysis was performed using the same VOIs with OncoAnalysis Horos Plugin (Computational Clinical Imaging Group,
Champalimaud).
The following semiquantitative parameters based on signal intensity time curves were extracted for both groups: wash-in slope,
wash-out slope,
area under the curve (AUC),
maximum enhancement (MaxEnh) and time to peak (TTP).
Statistical analysis
Using descriptive analysis baseline characteristics were assessed.
The independent samples T-test was used to compare means between the GDF and GDB patients.
IBM Statistical Package for the Social Sciences (SPSS,
version 22.0 Inc,
Chicago,
IL) was used for all statistical analyses.
A p-value ≤0.05 was considered statistically significant.