Joint Annual Research Report 2005 - The Royal Marsden

IMAGING RESEARCH & CANCER DIAGNOSIS – MAGNETIC RESONANCE
Figure 2. A representation of a
tumour or tissue displaying
heterogeneous cellularity. The
mean path length ‘L’ travelled by
protons in the extracellular fluid
within a specific observation time is
much greater in regions of low
cellularity where random motion is
not impeded by the presence of
cellular membranes.
L
L
proton
highly cellular region
mean path length L
proton path
Imaging tissue cellularity
and cell death
Diffusion-weighted MRI
Diffusion-weighted magnetic
resonance imaging (DW-MRI)
provides image contrast through
measurement of the properties
of water within tissues. In a highly
cellular tissue, water cannot diffuse
far during the MR observation
period without being blocked by
cell membranes (see Figure 2).
Conversely, in cystic or necrotic
tissues with fewer structural barriers,
the diffusional path-length of
extracellular water is longer. Apparent
diffusion coefficient (ADC) maps,
derived from DW-MRI, therefore
provide a non-invasive measure of
cellularity. In cancer imaging this
has potential for diagnosis, treatment
planning and monitoring response.
This approach is proving valuable,
as changes in ADC values are
measurable earlier than conventional
imaging response indicators.
DW-MRI can be exploited to
improve tumour detection
and differentiate benign from
malignant lesions.
DW-MRI and tumour
detection
In prostate cancer, we have shown
that the addition of DW-MRI
identifies tumour lesions with greater
A
certainty than using conventional
imaging alone (see Figure 3).
Additionally, the ADC values of
malignant prostate nodules appear
to be lower than those of nonmalignant
prostate nodules; we are
validating our results with
prostatectomy (this work is funded
by the Royal Marsden Hospital
Charity). We are also exploring ADC
as a measure of tumour aggressiveness
in patients opting to have their
prostate cancer actively monitored
(Cancer Research UK funded
surveillance programme led by
B
Figure 3. Primary prostate cancer:
Transverse T2W image (FSE 2096/90 msec [TR/effective TE] (A) and an isotropic ADC map (B)
at the same level through the prostate apex calculated from images (b = 0, 300, 500, 800
s/mm2) with diffusion weighted gradients sensitised in 3 planes. The tumour which is poorly
seen as an ill defined low signal intensity area on T2W (arrow) is clearly demarcated as an
area of restricted diffusion (arrow) on the ADC map.
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