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Measurements
of Nuclear and Cell Sizes, and Apparent Diffusion
Coefficient (ADC) Variations using Ultra-short Diffusion
Times.
We wish to thank Junzhong
Zu and Prof. John Gore at Vanderbilt University, Nashville, TN,
for sharing their NMR results, obtained with a Doty
Model 16-38 Z-gradient diffusion probe.
Diffusion-weighted magnetic resonance imaging (DWI) using an oscillating
gradient spin echo (OGSE) method can probe intracellular structures
which are usually not obtainable using conventional pulsed gradient
spin echo (PGSE) diffusion measurements (1,2). However, this technique
requires high gradient strength and slew rate, especially for high
frequency measurements, and those are not provided by conventional
gradient systems. The Doty PFG/diffusion Z-gradient coil satisfies
both requirements. Simulations and experiments show how this approach
can be used to measure mean cell and nuclear sizes (3).
Packed HL-60 cell sample pellets were studied using a 7.0 T, 16
cm bore Varian INOVA spectrometer equipped with a Doty Model 16-38
Z-gradient Diffusion probe, with strength up to 1500 G/cm. A cosine-modulated
OGSE non-imaging pulse sequence was used with three frequencies (500
Hz, 750 Hz, 1 kHz) and eleven b values evenly ranging from zero to
1000 s/mm2. TR=3 s, TE=64 ms, and each gradient duration=20 ms. Data
shown in Figure 1.
Figure 1. Experimental (markers) and fitted (lines) signal attenuation
as a function of diffusion gradient amplitudes and frequencies
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The fitted mean nuclear size
and cell size from diffusion measurements are 7.52±2.16 μm
and 11.18±0.02 μm.
These values are close to the values obtained from the light microscopy
data, 8.37±3.91 μm
and 10.22±2.44 μm,
Figure 2. For reference, the mean HL-60
cell size was reported to be 11.0 μm
in a previous study using light microscopy (4).
Figure
2. (a) H&E
stained cell slice. (b) Segmented image. (black:
nuclei, gray: cytoplasm and white:
extracellular space)
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In a separate study of two
phases of HL-60 cells, a conventional PGSE measurement did not
distinguish between cells in an arrested
S phase, and those in an M phase undergoing cell division. Averaged
ADC's of the two types of sample obtained by the PGSE method were
not significantly different, Figure 3. On the contrary, ADC's obtained
using the OGSE method are significantly different, especially at
relatively higher frequencies, Figure 4. Samples were controlled
to have same cell densities, implying that intracellular structure
changes occurring during cell division affect the water ADC at ultra-short
diffusion times.
Figure 3. Signal attenuation obtained by PGSE meas-urements
of two synchronized cell samples with b values up to 10,000s/mm2
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Figure 4. Dispersion curves
(ADC vs f) of two types of synchronized cells. Error
bars show standard devia-tions of all six samples
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This new OGSE approach provides structural parameters and additional
imaging contrast which may be helpful for detecting cancer, the assessment
of tumor malignancy, tracking intracellular changes in tissues, and
potentially monitoring tumor response to treatment in vivo.
Work of:
J. Xu1, J. Xie1, K. Li1,
J. Jourquin2,
D.C. Colvin1, Does1, D.
F. Gochberg1, V. Quaranta2, and J. C. Gore1
1Institute of Imaging Science, Vanderbilt University, Nashville,
TN, United States, 2Cancer Biology, Vanderbilt University, Nashville,
TN, United States
(1) Parsons et al. Magn Reson Med 2006
(2) Xu et al. Magn Reson Med 2009
(3) Xu et al. J Magn Reson 2009
(4) Galons et al. Magn Reson Med 2005
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