Shirin Sabouri1, Ladan Fazli2,3, Silvia Chang4,5, Richard Savdie3, Edward Jones6, Larry Goldenberg2,3, and Piotr Kozlowski2,3,4,7
1Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada, 2Vancouver Prostate Centre, Vancouver, BC, Canada, 3Urologic Sciences, University of British Columbia, Vancouver, BC, Canada, 4Radiology, University of British Columbia, Vancouver, BC, Canada, 5Vancouver General Hospital, Vancouver, BC, Canada, 6Pathology, Vancouver General Hospital, Vancouver, BC, Canada, 7UBC MRI Research Center, Vancouver, BC, Canada
Synopsis
Measurement
of relative amount of lumen in prostatic tissue can provide useful information
for diagnosing of many prostatic diseases. Using multi-exponential T2 mapping, the fractional volume of
the luminal space, or so called luminal water fraction (LWF), in the prostatic tissue
can be determined. In order to use the LWF as a proportional representative of the true percentage of
lumen, it is important to
investigate the correlation between the two parameters. We have acquired and
analyzed MR images of 10 subjects,
and found a significant correlation between the LWF and the percentages of lumen in tissue.Target Audience
Clinicians and
researchers interested in characterization of prostatic tissue
Purpose
To explore
the relationships between MR measurements from multi-exponential T
2 mapping
and the underlying tissue composition in prostate
Introduction
MR multi-exponential T
2 mapping is a
well-known imaging technique that has been applied for tracking
histo-pathological changes in organs such as brain
1. This technique can also be
used for extracting valuable information about tissue composition in prostate. In
the glandular tissue of prostate T
2 decay is bi-exponential, with
two distinguishable T
2 relaxation times
2. A longer T
2 component is related to the water protons
residing inside the lumen, while a shorter T
2 component is related to the water protons residing
within the epithelial and stromal tissue (see Figure 1). Using multi-exponential
T
2 mapping, the fractional volume of the luminal space, or so called
luminal water fraction (LWF), in the prostatic tissue can be determined. In
this study, we hypothesized that the LWF measured with MRI correlates with the
true percentage of lumen in the tissue. To validate this hypothesis, we have
acquired and analyzed MR images of 10 subjects, and evaluated the correlation
between MR measurements and the true percentages of underlying tissue compositions.
Particularly, we evaluated the correlation between LWF and the percentage of
lumen in tissue.
Methods
Data acquisition was carried out at the University
of British Columbia (UBC) MRI Research Centre, using a 3.0T whole body MR scanner [Achieva 3.0T,
Philips Medical Systems, Best, The Netherlands]. Ten patients with biopsy
proven cancer underwent MRI scan with an endorectal coil, prior to undergoing
prostatectomy. A 3D
multi-echo spin echo sequence
(TR/TE=3061/25ms, NE=64, FOV=240x240x40mm
3,
voxel-size=1x1x4mm
3, matrix-size=240x240) was used for scanning of
the entire prostate gland. Images were analyzed with Matlab [The MathWorks
Inc,Natick, MA, USA]. The analysis involved regularized Non-Negative Least
Squares (NNLS)
3,4 fitting of multi-exponential decay curves, which
generated T
2 distributions for every pixel (see Figure 2). The
following parameters were defined and used to describe the T
2
distribution of each pixel: number of distinguishable T
2 components
(N) determined by counting the number of peaks in the distribution; geometric
mean of the short (T
2-short) and long (T
2-long)
components, as well as the geometric mean of the entire distribution (gmT
2);
ratio of area under the long component over the total area under the entire
distribution (LWF); and areas under the short (A
1) and long (A
2)
components. Average values of these parameters were calculated within 211 ROIs manually
outlined on digitized images of the whole-mount histology sections with
histologic resolution, registered to MRI images
5. Percentage area of
tissue components including lumen, nuclei, and epithelial cytoplasm plus stroma,
were measured on digitized whole mount histology sections by using image
segmentation with DIH software [Leica Microsystems Inc., Germany]
(see Figure 3). Statistical analyses were performed with MedCalc [MedCalc
Software, Mariakerke, Belgium]. Correlations between
MR parameters and percentage area of tissue components were evaluated with
Spearman’s rank correlation test.
Results and Discussions
A
2,
LWF, T
2-short, gmT
2, and N significantly correlated with the
percentage of lumen, with the highest
correlation obtained for LWF (0.809, p<0.001); Figure 4 demonstrates the
scattered diagram of LWF versus area percentage of lumen. Area percentage of nuclei did not have
significant correlation with any of the MR parameters, with the exception of A1 (0.387, p<0.001). Finally, the area
percentage of epithelial cytoplasm plus stroma had significant correlation with A
2, LWF, T
2-short,
and gmT
2, with the highest correlation
obtained for gmT
2 (-0.639,
p<0.001).
In conclusion, the results of this pilot study demonstrate
that LWF measured with MRI is significantly correlated with the percentage area
of lumen in the prostatic tissue. Therefore, the methodology established in
this study for measuring LWF, may be useful in diagnosing various prostatic
diseases, including prostate cancer, in which the amounts of lumen differs between
normal and abnormal tissues.
Acknowledgements
This
study has been supported by the Canadian Institutes of Health Research. The
authors thank Dr. Antonio Hurtado for his assistance in statistical analysis of
digitized whole-mount histology sections.References
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