repeatability of echo-planar-based diffusion measurements of the human prostate at 3 t

Magnetic Resonance Im

Repeatability of echo-planar-based diffusion measurements of the

human prostate at 3 T

Peter Gibbs4, Martin D. Pickles, Lindsay W. TurnbullCenter for MR Investigations, Division of Cancer, Postgraduate Medical School, University of Hull, Hull, HU3 2JZ, UK

Received 1 February 2007; revised 20 March 2007; accepted 21 March 2007

Abstract

Echo-planar-based diffusion-weighted imaging (DWI) of the prostate is increasingly being suggested as a viable technique,

complementing information derived from conventional magnetic resonance imaging methods for use in tissue discrimination. DWI has

also been suggested as a potentially useful tool in the assessment of tumor response to treatment. In this study, the repeatability of apparent

diffusion coefficient (ADC) values obtained from both DWI and diffusion tensor imaging (DTI) has been assessed as a precursor to

determining the magnitude of treatment-induced changes required for reliable detection. The repeatability values of DWI and DTI were found

to be similar, with ADC values repeatable to within 35% or less over a short time period of a few minutes and a longer time period of a

month. Fractional anisotropy measurements were found to be less repeatable (between 26% and 71%), and any changes duly recorded in

longitudinal studies must therefore be treated with a degree of caution.

D 2007 Elsevier Inc. All rights reserved.

Keywords: Diffusion imaging; Tensor imaging; Prostate; Repeatability

1. Introduction

In 2004, an estimated 230,000 new cases of prostate

cancer will have been diagnosed in the United States

alone. Prostate cancer rates have risen dramatically over

the previous 10–15 years, initially as a result of the

widespread use of prostate-specific antigen blood testing

but most recently due to increasing prevalence in the

under-65-year age group [1]. With the advent of whole-

body MR scanners operating at field strengths of z1.5 T,

magnetic resonance imaging (MRI) of the human prostate

has become increasingly used for tumor localization and

staging [2]. However, the efficacy of conventional and

dynamic contrast-enhanced MRI is somewhat reduced due

to the overlapping characteristics of prostatic carcinoma,

prostatitis and benign prostatic hyperplasia.

An alternative approach may involve the application of

diffusion-weighted imaging (DWI), which is now seeing

wide applications in the brain. Over the last few years, a

0730-725X/$ – see front matter D 2007 Elsevier Inc. All rights reserved.

doi:10.1016/j.mri.2007.03.030

4 Corresponding author. Centre for MR Investigations, Hull Royal

Infirmary, HU3 2JZ Hull, UK. Tel.: +44 1482 674085; fax: +44 1482

320137.

E-mail address: [email protected] (P. Gibbs).

number of authors have demonstrated the feasibility of

diffusion imaging of the prostate [3–8]. A recent article has

also outlined some preliminary results of diffusion tensor

imaging (DTI) in the prostate [9]. Significant differences in

apparent diffusion coefficient (ADC) values between the

anatomically distinct peripheral zone and the central gland

have been demonstrated [3,4,9]. While significant differ-

ences in mean ADC values have been shown to exist

between cancerous and noncancerous areas of peripheral

zone tissues [4,6,7], it is evident that a large degree of

overlap exists between individual values. As such, it appears

unlikely that diffusion imaging will be utilized as a stand-

alone diagnostic tool. Rather, it is more likely to be utilized

as one of many diagnostic tools, as shown by Chan et al. [5].

A further application for diffusion imaging may lie in

the rapidly expanding field of MRI-based assessment and/

or prediction of tumor response to treatments such as

hormonal therapy and/or radiotherapy. A number of recent

articles have explored this possibility in small animal

models [10–12]. Dodd and Zhao [10] have shown

significant increases in ADC values prior to any reduction

in tumor volume after the treatment of a mouse model and

a rat model with fractionated radiotherapy. Jennings et al.

[11] reported that ADC values increased significantly only

aging 25 (2007) 1423–1429

P. Gibbs et al. / Magnetic Resonance Imaging 25 (2007) 1423–14291424

2 days after treatment initiation with docetaxel in an SCID

mouse model.

It is clear that if any quantitative parameter is to be used

as a means to assess tumor response, an indication of its

reproducibility and repeatability is a prerequisite. An

assessment of reproducibility, which can be regarded as

investigation results obtained with the same methodology

but in different laboratories, is beyond the scope of this

article. This work is concerned with determining repeat-

ability, wherein independent test results on identical items

obtained with the same method in the same laboratory are

compared [13]. A repeatability assessment would enable the

magnitude of treatment-induced change required for reliable

detection to be established. Experiments assessing the

repeatability and/or reproducibility of DTI measurement in

the brain have already been reported in the literature

[14,15]. Both of these studies reported coefficients of

variation of a few percentages only, indicating the reliability

of DTI in the brain. Indeed, Rana et al. [16] have suggested

that ADC measurements are potentially more robust than

lesion volume estimates. While encouraging, it is important

to note that these results cannot be extrapolated as prostate

images are obtained with a much lower signal-to-noise ratio

(SNR). Indeed, this is possibly the primary reason why

diffusion imaging of the prostate has been limited in its

application so far, since a low SNR necessitates an

increased number of averages and, thus, extended imaging

time [9]. Investigation of the repeatability of ADC measure-

ments outside the brain is currently limited to a couple of

studies in the abdomen [17] and rat kidney [18]. To date,

there appears to be no published work assessing the

repeatability of diffusion imaging in the prostate. This

article seeks to address this issue by exploring both

medium-term and short-term repeatability in the DWI and

DTI of the prostate. In this study, a 3.0-T whole-body

scanner and parallel imaging techniques are employed to

enable DWI and DTI, with sufficient SNR, in clinically

acceptable imaging times.

2. Methods

All imaging was performed using a GE Signa EXCITE

3.0-T whole-body scanner (GE Healthcare, Milwaukee,

WI) fitted with zoom gradients and an eight-channel torso

phased-array coil (USA Instruments, Inc., Aurora, OH).

Eight asymptomatic volunteers (mean age, 35 years; range,

29–49 years) were imaged on two separate occasions

approximately 1 month apart (mean, 30 days; range, 22–

38 days). After initial localizer scans, high-resolution T2-

weighted images were acquired for organ visualization

using an FSE-XL sequence (TE/TR=94.0/3520 ms; matrix

size=384�288; field of view=20�20 cm; slice thick-

ness=3.0 mm; average=4; receiver bandwidth=F41.7 kHz;

ETL=17). Eighteen slices detailing the prostate and

surrounding anatomy were obtained in just over 4 min.

DTI was then implemented using a single-shot spin-echo

echo-planar imaging (EPI) sequence with diffusion gra-

dients applied as a bipolar pair on either side of a

refocusing 1808 pulse. Parallel imaging was employed with

an ASSET factor of 2. Other acquisition parameters were as

follows: TE/TR=64.8 ms (fractional echo)/6200 ms; matrix

size=128�128; field of view=35�35 cm; slice thick-

ness=2.7 mm; average=6; receiver bandwidth=F250 kHz.

Images were obtained with b-factors of 0 and 700 s/mm2,

with diffusion gradients applied in six different directions.

The total acquisition time for DTI sequence was 4.5 min for

28 contiguous slices. Finally, DWI was performed again

using a single-shot spin-echo EPI sequence with an ASSET

factor of 2 and bipolar diffusion gradients. Images were

obtained with b-factors of 0 and 500 s/mm2, with diffusion

gradients applied along the anterior–posterior axis of the

body ( y-axis) only, due to time constraints. Other acquisi-

tion parameters included: TE/TR=65.7 ms (fractional echo)/

4000 ms; matrix size=224�224; field of view=26�26 cm;

slice thickness=5 mm; slice gap=1 mm; average=16;

receiver bandwidth=F250 kHz. The total acquisition time

was 2 min for seven slices. In all volunteers, DTI and DWI

were both performed twice on the second visit to enable

assessment of short-term repeatability. Finally, one volun-

teer was scanned using the DWI protocol described above

but with varying number of excitations (NEX). Five series

of images at each of 16, 8, 4, 2, and 1 NEX were obtained

to enable an assessment of the repeatability of ADC

measurement with respect to image SNR.

After acquisition, all images were transferred to an

Advantage Windows Workstation (GE Healthcare) for

subsequent processing with commercially available soft-

ware. Using conventional T2-weighted images as an

anatomical reference, tissues encompassing regions of

interest (ROI) were drawn, on the most representative slice

for each tissue type, in the normal peripheral zone and in the

central gland (excluding the urethra). Care was taken to

ensure region correspondence across all three datasets for

both DWI and DTI acquisitions by continual referencing to

previously drawn ROI. To assess the impact of ROI size on

ADC repeatability, regions were drawn on the peripheral

zone using a small constant size circle, a single lobe and,

finally, both lobes for all acquisitions acquired with varying

NEX in a single volunteer as described above. From DWI

results, the ADC in the y direction (ADCy) was calculated;

from DTI data, orientationally averaged diffusion coefficient

or mean diffusivity, fractional anisotropy (FA) and trace

elements (Dxx, Dyy, and Dzz) were computed.

The amount of agreement between measurements (both

short term and medium term) was determined by calculating

the standard deviation of mean differences. Bias was also

qualitatively assessed using Bland–Altman plots of average

values against the difference between measurements for all

parameters [19]. Repeatability was estimated using the

methodology previously described by Bland and Altman

[20] wherein it is calculated as 2.77 times the common

standard deviation of repeated measures. The common

Fig. 1. Bland–Altman plot of short-term variation in ADCy for the

peripheral zone. The mean difference of measurements (—) and F2 S.D. of

the mean difference (2222) are indicated.

Fig. 3. Bland–Altman plot of medium-term variation in mean diffusivity for

the peripheral zone. The mean difference of measurements (—) and F2

S.D. of the mean difference (2222) are indicated.

P. Gibbs et al. / Magnetic Resonance Imaging 25 (2007) 1423–1429 1425

standard deviation of repeated measures is often referred to

as within-subject standard deviation. This methodology has

previously been utilized in a study examining the repro-

ducibility of pharmacokinetic parameter calculation in

human muscles and tumors [21]. Differences between tissue

types for various parameters were also explored using

Wilcoxon signed ranks test.

3. Results

DWI and DTI were successfully implemented in all

volunteers. Significant differences, as determined using the

Wilcoxon signed ranks test, were noted between the

peripheral zone and the central gland for all calculated

parameters, namely, ADCy (P=.017), mean diffusivity

Fig. 2. Bland–Altman plot of short-term variation in ADCy for the central

gland. The mean difference of measurements (—) and F2 S.D. of the mean

difference (2222) are indicated.

(P=.012), FA (P=.012), Dxx (P=.017), Dyy (P=.012)

and Dzz (P=.017).

For all parameters, there was no evidence of bias

between acquisitions in either the short term or the medium

term. Sample Bland–Altman plots of the short-term repeat-

ability of ADC measurement using DWI for the peripheral

zone and the central gland are shown in Figs. 1 and 2,

respectively. There appears to be no bias present in these

results since zero lies comfortably within the F2 S.D.

interval. Similarly, Figs. 3 and 4 detail the medium-term

repeatability of mean diffusivity values in the peripheral

zone and the central gland, respectively. Again there is no

evidence of experimental bias. Repeatability can be assessed

in a qualitative fashion from the images shown in Fig. 5.

From both spin-echo EPI images (Fig. 5A–C) obtained with

Fig. 4. Bland–Altman plot of medium-term variation in mean diffusivity for

the central gland. The mean difference of measurements (—) and F2 S.D.

of the mean difference (2222) are indicated.

Fig. 5. Sample spin-echo EPI images (with b =0 s/mm2) obtained from a volunteer. The initial scan (A) is followed by two further scans (B and C) taken a few

minutes apart 1 month later. The corresponding ADCy maps are also illustrated (D–F), with the bladder (BL), central gland (CG) and peripheral zone (PZ)

highlighted. ADC values range from 0 (black) to N1.84 mm2/s (red). (For interpretation of the references to color in this figure legend, the reader is referred to

the web version of this article.)


b =0 s/mm2 and ADCy maps (Fig. 5D–F), excellent

delineation of the peripheral zone and the central gland is

evident. The bright inner area in the central gland denotes

Fig. 6. Consecutive spin-echo EPI images (A–C) obtained from a volunteer, acquir

corresponding ADCy maps (D–F). ADC values range from 0 (black) to N1.84 mm

the reader is referred to the web version of this article.)

the urethra, which is thus simply avoided during ROI

generation. Fig. 6 shows consecutive spin-echo EPI images

(Fig. 6A–C) and corresponding ADCy maps (Fig. 6D–F)

ed at one time point showing poor delineation of the peripheral zone and the2/s (red). (For interpretation of the references to color in this figure legend,

Table 1

Calculated diffusion imaging parameters and their short-term repeatability

for the peripheral zone and the central gland

Parameter Mean Mean

difference

F2 S.D. of

the difference

Repeatabilitya

Peripheral zone

ADCy (�10�3 mm2/s) 1.56 �0.06 �0.52 to 0.40 0.45 (29)

Mean diffusivity

(�10�3 mm2/s)

1.62 �0.02 �0.23 to 0.19 0.20 (13)

Dxx (�10�3 mm2/s) 1.57 0.03 �0.37 to 0.42 0.38 (24)

Dyy (�10�3 mm2/s) 1.68 �0.10 �0.49 to 0.30 0.39 (23)

Dzz (�10�3 mm2/s) 1.60 0.00 �0.17 to 0.17 0.16 (10)

FA 0.155 �0.023 �0.232 to 0.187 0.081 (52)

Central gland

ADCy (�10�3 mm2/s) 1.21 0.00 �0.19 to 0.18 0.18 (15)

Mean diffusivity

(�10�3 mm2/s)

1.27 �0.03 �0.25 to 0.19 0.22 (17)

Dxx (�10�3 mm2/s) 1.21 0.02 �0.34 to 0.37 0.35 (29)

Dyy (�10�3 mm2/s) 1.27 �0.10 �0.53 to 0.34 0.42 (34)

Dzz (�10�3 mm2/s) 1.35 �0.03 �0.22 to 0.16 0.18 (13)

FA 0.249 �0.033 �0.100 to 0.033 0.065 (26)

a Percentages are presented inside parentheses.

Table 3

Calculated prostate ADCy values (�10�3 mm2/s) and their repeatability for

various NEX and ROI size

Mean Mean

difference

F2 S.D. of

the difference

Repeatabilitya

Peripheral zone

Both lobes, 16 NEX 2.64 �0.02 �0.05 to 0.01 0.03 (1)

Both lobes, 1 NEX 2.92 �0.05 �0.37 to 0.30 0.31 (11)

One lobe, 16 NEX 2.65 �0.03 �0.13 to 0.07 0.10 (4)

One lobe, 1 NEX 2.98 0.01 �0.17 to 0.19 0.17 (6)

Small ROI, 16 NEX 2.71 �0.01 �0.08 to 0.05 0.06 (2)

Small ROI, 1 NEX 2.99 0.04 �0.24 to 0.32 0.27 (9)

Central gland

16 NEX 1.79 0.01 �0.06 to 0.07 0.06 (4)

8 NEX 1.82 0.02 �0.05 to 0.09 0.07 (4)

4 NEX 1.94 0.00 �0.16 to 0.16 0.16 (8)

2 NEX 1.99 �0.03 �0.27 to 0.21 0.23 (12)

1 NEX 2.14 0.00 �0.22 to 0.22 0.22 (10)



demonstrating poorer discrimination between the central

gland and the peripheral zone in another subject.

The results of repeatability assessment are summarized in

Table 1 (short-term repeatability), Table 2 (medium-term

repeatability) and Table 3 (repeatability dependence on ROI

size and SNR). From Tables 1 and 2, it is noted that central

gland ADCy measurements are more repeatable (15% or

better) than the corresponding peripheral zone ADCy values

(32% or better). Calculated mean diffusivities appear to be

more robust than individual trace elements Dxx and Dyy for

both tissue types in the short term and in the medium term.

Dzz values have repeatability similar to corresponding mean

diffusivities. FA was found to be the most unreliable

parameter calculated, with a repeatability of 26–71%. From

Table 3, it is observed that as the number of averages (hence

SNR) is decreased, repeatability worsens from 4% to 10%.

Table 2

Calculated diffusion imaging parameters and their medium-term repeat-

ability for the peripheral zone and the central gland

Parameter Mean Mean

difference

F2 S.D. of

the difference

Repeatabilitya

Peripheral zone

ADCy (�10�3 mm2/s) 1.63 0.19 �0.33 to 0.72 0.51 (32)

Mean diffusivity

(�10�3 mm2/s)

1.59 �0.04 �0.37 to 0.30 0.32 (20)

Dxx (�10�3 mm2/s) 1.55 �0.05 �0.43 to 0.33 0.37 (24)

Dyy (�10�3 mm2/s) 1.63 �0.01 �0.54 to 0.53 0.52 (32)

Dzz (�10�3 mm2/s) 1.58 �0.05 �0.37 to 0.27 0.31 (20)

FA 0.156 0.025 �0.088 to 0.138 0.111 (71)

Central gland

ADCy (�10�3 mm2/s) 1.26 0.09 �0.09 to 0.27 0.18 (14)

Mean diffusivity

(�10�3 mm2/s)

1.23 �0.06 �0.39 to 0.27 0.30 (25)

Dxx (�10�3 mm2/s) 1.17 �0.09 �0.51 to 0.33 0.41 (35)

Dyy (�10�3 mm2/s) 1.22 0.00 �0.40 to 0.39 0.39 (32)

Dzz (�10�3 mm2/s) 1.29 �0.08 �0.41 to 0.25 0.33 (25)

FA 0.273 0.082 �0.017 to 0.181 0.097 (35)


ROI size varied from 120 mm2 for a small circle to ~320

mm2 for a single lobe and ~640 mm2 for both lobes of the

peripheral zone. Changing the size of user-defined ROI

appears to have little impact on repeatability.

4. Discussion

MRI is increasingly being purported as a noninvasive

tool for treatment monitoring of cancer [22,23]. A reliable

assessment of response necessitates the use of a measurable

parameter, which is sensitive to broad variations in the

attribute studied (large between-patient variance) while also

demonstrating small variations in repeatability studies

(small within-patient variance). Quantification of tumor

volume utilizing high-resolution imaging is probably the

most repeatable parameter that can be readily assessed with

MRI. However, it is well understood that pretreatment

tumor volume is not always the best predictor of short-term

response [24]. As well as other functional MR methods such

as R2* mapping and pharmacokinetic modeling, diffusion

imaging offers an alternative possibility [25]. Diffusion

imaging also has the added benefit of not requiring contrast

agent administration.

This work has attempted to quantify the degree of change

required in ADC values to be reliably assured that any

observed variations with treatment are true effects and not

attributable to measurement error. The repeatability of ADC

values (ADCy, Dxx, Dyy and Dzz) appears to be between

10% and 35% from the data presented in Tables 1 and 2.

It is instructive to look at the results obtained in more

detail and to investigate any potential sources of error. ADC

values determined from DWI appear to be more repeatable in

the central gland (15%) than in the peripheral zone (32%)

over both the short term and the medium term. In at least one

volunteer, the peripheral zone was poorly defined (Fig. 6),

making accurate region delineation problematic. From Fig. 1,

it can be seen that all short-term variations in peripheral zone

ADC values are within 0.15�10�3 mm2/s apart from one


case. Exclusion of this volunteer results in a repeatability of

0.19�10�3 mm2/s (or 12%)— a figure more in line with that

obtained in the central gland. Medium-term variations in

ADC values for the peripheral zone appear to be greater and

can probably be attributed to variations in the amount of

rectal gas present. This results in differences in the

magnitude of susceptibility artifact present, most especially

in the peripheral zone due to its proximity to the rectum. This

emphasizes the need to ensure that all volunteers and

prospective patients are scanned with minimal air in the

rectum. Other potential confounding factors, including the

degree of bladder filling, should also be controlled as much

as possible between intrasubject visits.

In DWI experiments, the ADC value has been quantified

in one direction only (namely, the y direction or the

anterior–posterior direction) due to time constraints in data

acquisition. However, it is unlikely that changes in

volunteer positioning will have anything more than a

limited affect on the ADC values obtained. Primarily, there

is minimal scope for variation in the orientation of the

prostate within the bore of the scanner. However, orientation

changes may occur in patients over time due to organ

shrinkage as the prostate gland responds to treatment.

Clearly, ramifications of this effect must be considered

carefully, with respect to opting between DWI and DTI,

before any treatment study commences.

For DTI experiments, the repeatability of mean diffu-

sivity values varies from 13% to 25%, and the repeatability

of individual trace elements varies between 10% and 35%.

In both the medium term and, most especially, the short

term, Dzz appears to be the most repeatable of the trace

elements for both the peripheral zone and the central gland.

This may be related to the different gradient technology

employed in the z direction compared to the x and y

directions. As probably expected, FA appears to be the

parameter with the worst repeatability, with changes of

between 26% and 71% being required to be certain of a

true treatment-induced effect. While FA is higher in the

central gland than in the peripheral zone for all volunteers

(a difference noted to be statistically significant; P=.012),

changes in FA values must be treated with a degree of

caution due to calculated repeatability values. Other work-

ers have reported excellent repeatability of FA measure-

ments in the brain [15,26–28], but these studies were

implemented under much better SNR conditions.

Summarizing Tables 1 and 2, the repeatability of ADC

values in the human prostate appears to be 35% or better,

depending on experimental conditions. These values may

seem inordinately high, especially in comparison with

Jennings et al. [11], who reported the reproducibility of

ADC values to be around 5% in anesthetized rats. However,

it has to be borne in mind that this work was implemented at

a higher field strength (4.7 T) in an animal model.

Although data only on normal volunteers have been

obtained, it is reasonable to assume that the results can be

extended to prostate tumors. It is difficult to assess medium-

term repeatability in prostatic tumors since disease progres-

sion may occur within this time frame. However, it is clear

that delineation and analysis of prostatic tumor ROI will be

no easier than those for normal prostatic tissues, potentially

resulting in poorer repeatability.

Having determined the repeatability of ADC measure-

ments in the prostate, it is important to compare these results

to published treatment-induced changes in ADC values.

Jennings et al. [11] reported an increase in diffusion from

0.81�10�3 to 1.18�10�3 mm2/s (a 46% increase) following

treatment with 10 mg/kg docetaxel in SCID mice with

prostate cancer xenografts. Dodd and Zhao [10] detailed an

average change in ADC value from 0.55�10�3 to

1.15�10�3 mm2/s (a 110% increase) in Dunning rat AT6

prostate tumors treated with eight fractions (3 Gy per

fraction) of radiotherapy over 10 days. Following photody-

namic therapy (PDT), the mean ADC values of human

prostatic adenocarcinoma xenografts declined by approxi-

mately 25% after 7 h, according to Plaks et al. [12]. This

study also noted that 48 h post-PDT, ADC values had

increased by 180% compared to before-treatment values,

correlating with the development of hemorrhagic necrosis.

From these articles, the ability to detect changes of around

30% appears sufficient to monitor prostatic tumor response

to various treatment regimes.

Some of the potential limitations of this work are worth

noting. All the results detailed here have been obtained

using a minimal range of experimental conditions, namely,

on healthy volunteers at 3.0 T using an echo-planar DWI

sequence without an endorectal coil. By assessing repeat-

ability over approximately 1 month, as well as over a few

minutes, it was assumed that the prostate remained stable

over this time period. However, it is unknown as to whether

hormonal and/or sexual activity could affect ADC measure-

ments. It is important to note, though, that these variables

are unlikely to be controlled for in any assessment of

diffusion changes during treatment response. When

performing DWI, some consideration must be given to the

selection of the most appropriate b-values. The b-values

selected in this work were based on the work described by

Xing et al. [29], wherein, for a two-point strategy, b-values

of 0 and ~1/ADC optimize the accuracy of the calculated

ADC value. Utilizing previous results [3–9], b-values of

between 500 and 700 s/mm2 are deemed most appropriate

for normal peripheral zone tissues. Because of the reduced

ADC in prostatic carcinoma, an increased b-value of 700–

800 s/mm2 may be more appropriate for a patient

population. Alternative acquisition sequences, such as fast

spin-echo imaging, warrant further investigation since it is

evident from Table 3 that SNR plays an important role in

determining repeatability. Varying the size of the ROI from

a small circle (120 mm2) through a single lobe (~320 mm2)

to both lobes of the peripheral zone (~640 mm2) appeared to

have little impact on repeatability. Clearly assessing

treatment response using ADC repeatability will depend

somewhat upon the ability to delineate prostatic carcinoma


from surrounding healthy or benign tissues. Unfortunately,

the extent of this problem is difficult to predict from

volunteer data, but it is probably safe to say that ADC

repeatability in prostate carcinoma will be no better than that

reported herein.

In conclusion, the use of a spin-echo EPI sequence, in

combination with parallel imaging technology, results in

reduced acquisition times for both DWI and DTI techniques,

thus minimizing any potential motion artifacts. The reduced

SNR obtained by employing parallel imaging methods is

offset by the use of a high-field whole-body scanner. This

article has shown that it is possible to obtain ADC values

from both DWI and DTI techniques in clinically acceptable

imaging times with a reasonable degree of repeatability.

Appropriate prescanning preparation of volunteers and

prospective patients may further improve this repeatability.

Acknowledgments

The authors would like to thank Yorkshire Cancer

Research for funding this work. We are also grateful to

Adrian Knowles of GE Healthcare for his assistance with

imaging protocol development.

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