DOI:10.2214/AJR.07.2512
AJR 2007; 189:1494-1501
© American Roentgen Ray Society
Diffusion-Weighted Imaging of the Appendicular Skeleton with a Non–Carr-Purcell-Meiboom-Gill Single-Shot Fast Spin-Echo Sequence
Ali Yusuf Öner1,
Levent Aggunlu1,
Sergin Akpek1,
Turgut Tali1 and
Azim Celik2
1 Department of Radiology, Gazi University School of Medicine, Besevler, Ankara
06510, Turkey.
2 GE Medical Systems, Istanbul, Turkey.
Received May 4, 2007;
accepted after revision June 1, 2007.
Presented at the 2007 annual meeting of the Radiological Society of North
America, Chicago, IL.
Address correspondence to A. Y. Öner
(yusuf{at}tr.net).
Abstract
OBJECTIVE. The objective of our study was to prospectively evaluate
the signal-to-noise ratio (SNR) improvement in diffusion-weighted imaging
(DWI) of the appendicular skeleton with the use of a newly developed
non–Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo
(SSFSE) sequence and to evaluate its effect on apparent diffusion coefficient
(ADC) measurements.
SUBJECTS AND METHODS. DWI of the bone was performed in 32 patients
with an echo-planar imaging (EPI)–based sequence followed by a non-CPMG
SSFSE technique. SNR and ADC values were measured over a lesion-free right
femoral head. A score was assigned for each set of images to assess image
quality. When a bone lesion was present, contrast-to-noise ratio (CNR) and ADC
were also measured. Paired Student's t tests were used for
statistical analysis.
RESULTS. The mean (± SD) SNR values were 9.89 ± 2.20
and 81.68 ± 4.87 for EPI and non-CPMG SSFSE DWI, respectively. SNR
values associated with the non-CPMG SSFSE technique were found to be
significantly higher than those measured with the EPI-based DWI technique
(p < 0.01). Mean ADCs of the bone were 0.57 ± 0.20 and 0.29
± 0.15 x 10–3 mm2/s, respectively,
for EPI and non-CPMG SSFSE DWI. Image quality scores were higher for the
non-CPMG SSFSE DWI technique (p < 0.05) than for the EPI-based DWI
technique. Overall lesion CNR was found to be higher in DWI performed with the
non-CPMG SSFSE technique.
CONCLUSION. The non-CPMG SSFSE technique provides a significant
improvement over the currently used EPI-based DWI technique and has the
potential to be a powerful tool in imaging the appendicular skeleton.
Keywords: appendicular skeleton • avascular necrosis • bone lesions • diffusion-weighted imaging • echo-planar imaging • MR techniques • parallel imaging • perfusion imaging
Introduction
MRI has an important role in the diagnosis and treatment follow-up of
different skeletal diseases, including tumors and inflammatory and infectious
diseases. However, the specificity of routine MRI sequences is limited because
of similar or sometimes identical signal intensities on T1- and T2-weighted
images in various musculoskeletal abnormalities. More recently,
diffusion-weighted imaging (DWI) together with perfusion imaging is promising
great potential in assessing the functional properties of different pathologic
processes and in establishing a differential diagnosis
[1–3].
DWI is based on the random motion of water protons and is successfully used
as an important diagnostic tool in the workup of different brain disorders
[4–6].
With its ability to detect altered water-proton mobility, DWI may also be
useful for the evaluation of appendicular skeletal disorders. The number of
research studies on bone DWI is limited, but DWI has been used for the
distinction of acute benign osteoporotic from malignant vertebral compression
fractures [7,
8]. There is also current
effort to implement DWI in the differential diagnosis and treatment follow-up
of different bone tumors [9,
10].
DW images are most commonly obtained using acquisition schemes based on
single- or multishot echo-planar imaging (EPI) methods
[11,
12]. EPI methods are used due
to a relatively good signal-to-noise ratio (SNR) achieved with a low
radiofrequency power deposition. On the other hand, EPI-based DWI suffers from
artifacts caused by susceptibility changes at tissue boundaries and from
geometric image distortions created by significant eddy currents arising from
the large magnetic field gradients used
[13]. Overall, these
EPI-related artifacts have a detrimental effect on image quality and can
interfere with diagnostic interpretation.
To overcome these EPI-related artifacts, we chose to use a newly developed
non–Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo
(SSFSE) sequence in DWI of the appendicular skeleton
[14]. Thus, the purpose of
this study was to prospectively evaluate the SNR and image quality
improvements in DWI of the appendicular skeleton with the use of this non-CPMG
SSFSE sequence and to evaluate its effect on apparent diffusion coefficient
(ADC) measurements.
Subjects and Methods
Patient Population
This study was approved by our institutional review board. Written informed
consent was obtained from all participants. Ten healthy volunteers and 22
patients suspected of having osteomyelitis, metastases, or avascular necrosis
(AVN) (three pyogenic osteomyelitis, three metastases, 16 AVN) were enrolled
in this study. The age range of the 22 men and 10 women in the study group was
from 22 to 73 years, with a mean age of 42 years. All patients with metastases
had histologically proven extraskeletal malignancies (breast cancer,
n = 2; lung cancer, n = 1). The diagnosis of osteomyelitis
was established histologically and by means of culture of tissue sampling. In
the 16 patients with AVN, AVN was located in the talus in four, in the femoral
head in 11, and in the lunate in one. In all these patients, the diagnosis was
established by the patient's history and compatible imaging features.
MRI Technique
All of the study subjects were examined with a 1.5-T superconducting MR
system (Signa Excite II, GE Healthcare) using a phased-array coil. The maximum
gradient strength was 33 mT/m, and the slew rate was 120 mT/m/s. All subjects
underwent DWI in addition to imaging with a routine MRI sequence. The MRI
protocol included T1- and T2-weighted images in the axial and sagittal planes
together with a fast spin-echo (FSE) inversion recovery sequence acquired in
the coronal or sagittal plane. Contrast agent was administered to six
patients, and contrast-enhanced T1-weighted images in the axial and sagittal
planes were also obtained.
DW images were obtained in the coronal or sagittal plane using a spin-echo
EPI DWI sequence (TR/TE, 8,000/80; section thickness, 7 mm; intersection gap,
1 mm; matrix, 160 x 160; number of excitations [NEX], 1; field of view,
20–36 cm; and b value, 0 and 600 mm2/s) followed by a
non-CPMG SSFSE DWI sequence (9,000/74; section thickness, 7 mm; intersection
gap, 1 mm; matrix, 160 x 160; NEX, 1; field of view, 20–36 cm; and
b value, 0 and 600 mm2/s).
The selection of a b value of 600 mm2/s was based on a
compromise between signal intensity and adequate diffusion strength. At both b
values, diffusion sensitization was repeated in each orthogonal gradient
direction (i.e., phase encoding, readout, section selection). All DWI
sequences were performed before contrast injection. Imaging time was 42
seconds for spin-echo EPI DWI and 50 seconds for non-CPMG SSFSE DWI.
Image Analysis
All images were analyzed in consensus by two experienced radiologists. To
assess the visual image quality, image quality scores using a 4-point scale
from 1 (excessive artifact and image distortion) to 4 (no artifact or image
distortion) were assigned for each data set. ADC maps were derived
automatically on a voxel-by-voxel basis using commercially available software
(Advantage Workstation, release 4.1; GE Healthcare). The ADC was calculated
with a linear regression analysis of the function S =
S0 x exp(–b x ADC),
where S is the signal intensity after application of the diffusion
gradient, S0 is the signal intensity at b = 0
mm2/s, and b is the diffusion factor.
For quantitative analysis, the SNR of a lesion-free bone was measured on
trace images (b = 600 mm2/s) of both DWI series. SNR was calculated
as follows: SNRbone = SIbone /
SDnoise. Bone signal intensity
(SIbone) was recorded as the value generated by placing a
circular region of interest (ROI) of 1 cm in diameter over the right femoral
head or central portion of the short bones on each DWI series. If a lesion was
found at the right femoral head, measurements were completed from the
contralateral femur or the adjacent normal-appearing diaphysis. An ROI placed
in the most artifact-free air area was taken as the noise, and its SD was used
for the SNR calculation (SDnoise). ADC values of normal
bone were obtained using the same ROIs established for signal intensity
measurements.
When a bone lesion was present, the contrast-to-noise ratio (CNR) and ADC
were also measured on both data sets. CNR was calculated as follows:
CNR =(SIlesion –
SIbone) / SDnoise. Lesion signal
intensity (SIlesion) was recorded as the value generated
by placing ROIs within the confines of the lesions using T1- and T2-weighted
FSE inversion recovery imaging guidance. ADC values of the lesions were
obtained using the same ROIs established for signal intensity
measurements.
Statistical Analysis
Statistical analysis was performed with commercially available statistical
software (SPSS version 11.0, SPSS). Differences in quantitative analysis
results obtained from the two different DWI data sets were assessed with the
paired Student's t test. A p value of 0.05 or less was
defined as significant.
Results
The SNR and ADC values obtained from normal bone with the two different DWI
sequences for a b value of 600 mm2/s and the corresponding image
quality scores are shown in Table
1. The SNR values associated with the non-CPMG SSFSE technique
were found to be significantly higher than those measured with the EPI-based
DWI technique (p < 0.01). The ADC measurements obtained with
EPI-based DWI were found to be significantly higher than those obtained with
the non-CPMG SSFSE DWI technique. Image quality scores were found to be higher
for the non-CPMG SSFSE DWI images than for the EPI-based DWI images. Images of
a patient with normal MRI findings are shown in Figures
1A,
1B,
1C, and
1D.
View this table:
[in this window]
[in a new window]
|
TABLE 1: Signal-to-Noise Ratio (SNR) and Apparent Diffusion Coefficient (ADC)
Values of Normal Bone Measured by Two Diffusion-Weighted Imaging (DWI)
Sequences and Image Quality Scores
|
|
View larger version (168K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1A —32-year-old healthy male volunteer with normal MRI findings.
Coronal images obtained at same level with two different diffusion-weighted
imaging (DWI) techniques: echo-planar imaging (EPI) DWI (A) and
non–Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo
(SSFSE) DWI (B), both at b = 600 mm2/s, and corresponding,
respectively, to apparent diffusion coefficient (ADC) maps (C and
D). Increased signal with better background suppression is noted with
non-CPMG SSFSE technique. Mean ADC (± SD) for right femoral head is
0.54 ± 0.17 and 0.31 ± 0.14 x 10–3
mm2/s for EPI and non-CPMG SSFSE DWI, respectively. Please note
that images obtained with non-CPMG SSFSE technique have decreased
susceptibility-induced artifacts and increased signal-to-noise ratio compared
with EP images.
|
|
View larger version (122K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1B —32-year-old healthy male volunteer with normal MRI findings.
Coronal images obtained at same level with two different diffusion-weighted
imaging (DWI) techniques: echo-planar imaging (EPI) DWI (A) and
non–Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo
(SSFSE) DWI (B), both at b = 600 mm2/s, and corresponding,
respectively, to apparent diffusion coefficient (ADC) maps (C and
D). Increased signal with better background suppression is noted with
non-CPMG SSFSE technique. Mean ADC (± SD) for right femoral head is
0.54 ± 0.17 and 0.31 ± 0.14 x 10–3
mm2/s for EPI and non-CPMG SSFSE DWI, respectively. Please note
that images obtained with non-CPMG SSFSE technique have decreased
susceptibility-induced artifacts and increased signal-to-noise ratio compared
with EP images.
|
|
View larger version (175K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1C —32-year-old healthy male volunteer with normal MRI findings.
Coronal images obtained at same level with two different diffusion-weighted
imaging (DWI) techniques: echo-planar imaging (EPI) DWI (A) and
non–Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo
(SSFSE) DWI (B), both at b = 600 mm2/s, and corresponding,
respectively, to apparent diffusion coefficient (ADC) maps (C and
D). Increased signal with better background suppression is noted with
non-CPMG SSFSE technique. Mean ADC (± SD) for right femoral head is
0.54 ± 0.17 and 0.31 ± 0.14 x 10–3
mm2/s for EPI and non-CPMG SSFSE DWI, respectively. Please note
that images obtained with non-CPMG SSFSE technique have decreased
susceptibility-induced artifacts and increased signal-to-noise ratio compared
with EP images.
|
|
View larger version (136K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1D —32-year-old healthy male volunteer with normal MRI findings.
Coronal images obtained at same level with two different diffusion-weighted
imaging (DWI) techniques: echo-planar imaging (EPI) DWI (A) and
non–Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo
(SSFSE) DWI (B), both at b = 600 mm2/s, and corresponding,
respectively, to apparent diffusion coefficient (ADC) maps (C and
D). Increased signal with better background suppression is noted with
non-CPMG SSFSE technique. Mean ADC (± SD) for right femoral head is
0.54 ± 0.17 and 0.31 ± 0.14 x 10–3
mm2/s for EPI and non-CPMG SSFSE DWI, respectively. Please note
that images obtained with non-CPMG SSFSE technique have decreased
susceptibility-induced artifacts and increased signal-to-noise ratio compared
with EP images.
|
|
The CNR and ADC values for different bone lesions are shown in
Table 2. Overall lesion CNR was
found to be higher in DWI using the non-CPMG SSFSE technique. However,
statistical analysis based on lesion types was not possible due to the small
number of lesions included in this study. DW images of three patients with
different bone lesions are shown in Figures
2A,
2B,
2C,
2D,
2E,
3A,
3B,
3C,
3D,
3E,
4A,
4B,
4C,
4D, and
4E.
View this table:
[in this window]
[in a new window]
|
TABLE 2: Contrast-to-Noise Ratio (CNR) and Apparent Diffusion Coefficient (ADC)
Values Measured by Two Diffusion-Weighted Imaging (DWI) Sequences in Skeletal
Lesions
|
|
View larger version (97K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2B —46-year-old woman with right femoral head avascular necrosis
(AVN). Diffusion-weighted imaging (DWI) performed at same level with two
different techniques: echo-planar imaging (EPI)–based DWI (B) and
non–Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo
(SSFSE) DWI (C), both at b = 600 mm2/s, and corresponding,
respectively, apparent diffusion coefficient (ADC) maps (D and
E). AVN is more readily seen on non-CPMG SSFSE images than EP images.
Mean ADC (± SD) measured from left femoral head is 0.51 ± 0.12
and 0.32 ± 0.14 x 10–3 mm2/s for EPI
and non-CPMG SSFSE DWI, respectively. ADC measured from right femoral head is
1.49 ± 0.61 and 1.40 ± 0.51 x 10–3
mm2/s for EPI and non-CPMG SSFSE DWI, respectively. This reflects
increased diffusion due to accompanying bone marrow edema. Please note
increased contrast-to-noise ratio and higher image quality obtained with
non-CPMG technique.
|
|
View larger version (90K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2C —46-year-old woman with right femoral head avascular necrosis
(AVN). Diffusion-weighted imaging (DWI) performed at same level with two
different techniques: echo-planar imaging (EPI)–based DWI (B) and
non–Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo
(SSFSE) DWI (C), both at b = 600 mm2/s, and corresponding,
respectively, apparent diffusion coefficient (ADC) maps (D and
E). AVN is more readily seen on non-CPMG SSFSE images than EP images.
Mean ADC (± SD) measured from left femoral head is 0.51 ± 0.12
and 0.32 ± 0.14 x 10–3 mm2/s for EPI
and non-CPMG SSFSE DWI, respectively. ADC measured from right femoral head is
1.49 ± 0.61 and 1.40 ± 0.51 x 10–3
mm2/s for EPI and non-CPMG SSFSE DWI, respectively. This reflects
increased diffusion due to accompanying bone marrow edema. Please note
increased contrast-to-noise ratio and higher image quality obtained with
non-CPMG technique.
|
|
View larger version (116K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2D —46-year-old woman with right femoral head avascular necrosis
(AVN). Diffusion-weighted imaging (DWI) performed at same level with two
different techniques: echo-planar imaging (EPI)–based DWI (B) and
non–Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo
(SSFSE) DWI (C), both at b = 600 mm2/s, and corresponding,
respectively, apparent diffusion coefficient (ADC) maps (D and
E). AVN is more readily seen on non-CPMG SSFSE images than EP images.
Mean ADC (± SD) measured from left femoral head is 0.51 ± 0.12
and 0.32 ± 0.14 x 10–3 mm2/s for EPI
and non-CPMG SSFSE DWI, respectively. ADC measured from right femoral head is
1.49 ± 0.61 and 1.40 ± 0.51 x 10–3
mm2/s for EPI and non-CPMG SSFSE DWI, respectively. This reflects
increased diffusion due to accompanying bone marrow edema. Please note
increased contrast-to-noise ratio and higher image quality obtained with
non-CPMG technique.
|
|
View larger version (90K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2E —46-year-old woman with right femoral head avascular necrosis
(AVN). Diffusion-weighted imaging (DWI) performed at same level with two
different techniques: echo-planar imaging (EPI)–based DWI (B) and
non–Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo
(SSFSE) DWI (C), both at b = 600 mm2/s, and corresponding,
respectively, apparent diffusion coefficient (ADC) maps (D and
E). AVN is more readily seen on non-CPMG SSFSE images than EP images.
Mean ADC (± SD) measured from left femoral head is 0.51 ± 0.12
and 0.32 ± 0.14 x 10–3 mm2/s for EPI
and non-CPMG SSFSE DWI, respectively. ADC measured from right femoral head is
1.49 ± 0.61 and 1.40 ± 0.51 x 10–3
mm2/s for EPI and non-CPMG SSFSE DWI, respectively. This reflects
increased diffusion due to accompanying bone marrow edema. Please note
increased contrast-to-noise ratio and higher image quality obtained with
non-CPMG technique.
|
|
View larger version (140K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 3B —38-year-old man with lunate avascular necrosis (AVN).
Diffusion-weighted imaging (DWI) performed at same level with two different
techniques: echo-planar imaging (EPI)–based DWI (B) and
non–Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo
(SSFSE) DWI (C), both at b = 600 mm2/s, and corresponding,
respectively, apparent diffusion coefficient (ADC) maps (D and
E). AVN is more readily seen on non-CPMG SSFSE images than EP images.
Mean ADC (± SD) measured from capitate bone is 0.58 ± 0.19 and
0.31 ± 0.11 x 10–3 mm2/s for EPI and
non-CPMG SSFSE DWI, respectively. ADC measured from lunate is 1.53 ±
0.58 and 1.44 ± 0.49 x 10–3 mm2/s for
EPI and non-CPMG SSFSE DWI, respectively. Higher mean ADC values seen in
lunate reflect increased diffusion due to accompanying bone marrow edema.
|
|
View larger version (114K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 3C —38-year-old man with lunate avascular necrosis (AVN).
Diffusion-weighted imaging (DWI) performed at same level with two different
techniques: echo-planar imaging (EPI)–based DWI (B) and
non–Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo
(SSFSE) DWI (C), both at b = 600 mm2/s, and corresponding,
respectively, apparent diffusion coefficient (ADC) maps (D and
E). AVN is more readily seen on non-CPMG SSFSE images than EP images.
Mean ADC (± SD) measured from capitate bone is 0.58 ± 0.19 and
0.31 ± 0.11 x 10–3 mm2/s for EPI and
non-CPMG SSFSE DWI, respectively. ADC measured from lunate is 1.53 ±
0.58 and 1.44 ± 0.49 x 10–3 mm2/s for
EPI and non-CPMG SSFSE DWI, respectively. Higher mean ADC values seen in
lunate reflect increased diffusion due to accompanying bone marrow edema.
|
|
View larger version (164K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 3D —38-year-old man with lunate avascular necrosis (AVN).
Diffusion-weighted imaging (DWI) performed at same level with two different
techniques: echo-planar imaging (EPI)–based DWI (B) and
non–Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo
(SSFSE) DWI (C), both at b = 600 mm2/s, and corresponding,
respectively, apparent diffusion coefficient (ADC) maps (D and
E). AVN is more readily seen on non-CPMG SSFSE images than EP images.
Mean ADC (± SD) measured from capitate bone is 0.58 ± 0.19 and
0.31 ± 0.11 x 10–3 mm2/s for EPI and
non-CPMG SSFSE DWI, respectively. ADC measured from lunate is 1.53 ±
0.58 and 1.44 ± 0.49 x 10–3 mm2/s for
EPI and non-CPMG SSFSE DWI, respectively. Higher mean ADC values seen in
lunate reflect increased diffusion due to accompanying bone marrow edema.
|
|
View larger version (139K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 3E —38-year-old man with lunate avascular necrosis (AVN).
Diffusion-weighted imaging (DWI) performed at same level with two different
techniques: echo-planar imaging (EPI)–based DWI (B) and
non–Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo
(SSFSE) DWI (C), both at b = 600 mm2/s, and corresponding,
respectively, apparent diffusion coefficient (ADC) maps (D and
E). AVN is more readily seen on non-CPMG SSFSE images than EP images.
Mean ADC (± SD) measured from capitate bone is 0.58 ± 0.19 and
0.31 ± 0.11 x 10–3 mm2/s for EPI and
non-CPMG SSFSE DWI, respectively. ADC measured from lunate is 1.53 ±
0.58 and 1.44 ± 0.49 x 10–3 mm2/s for
EPI and non-CPMG SSFSE DWI, respectively. Higher mean ADC values seen in
lunate reflect increased diffusion due to accompanying bone marrow edema.
|
|
View larger version (147K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 4A —56-year-old woman with breast cancer involving right humerus.
Axial contrast-enhanced T1-weighted image shows strong contrast enhancement at
right humeral head consistent with metastasis.
|
|
View larger version (159K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 4B —56-year-old woman with breast cancer involving right humerus.
Diffusion-weighted imaging (DWI) performed in coronal plane with two different
techniques: echo-planar imaging (EPI) DWI (B) and
non–Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo
(SSFSE) DWI (C), both at b = 600 mm2/s, and corresponding,
respectively, apparent diffusion coefficient (ADC) maps (D and
E). Mean ADC (± SD) measured from humeral head is 1.07 ±
0.12 and 0.82 ± 0.17 x 10–3 mm2/s for
EPI and non-CPMG SSFSE DWI, respectively. These values are lower than those
measured in infectious process and avascular necrosis and reflect water
diffusion restriction by tumor cells.
|
|
View larger version (127K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 4C —56-year-old woman with breast cancer involving right humerus.
Diffusion-weighted imaging (DWI) performed in coronal plane with two different
techniques: echo-planar imaging (EPI) DWI (B) and
non–Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo
(SSFSE) DWI (C), both at b = 600 mm2/s, and corresponding,
respectively, apparent diffusion coefficient (ADC) maps (D and
E). Mean ADC (± SD) measured from humeral head is 1.07 ±
0.12 and 0.82 ± 0.17 x 10–3 mm2/s for
EPI and non-CPMG SSFSE DWI, respectively. These values are lower than those
measured in infectious process and avascular necrosis and reflect water
diffusion restriction by tumor cells.
|
|
View larger version (186K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 4D —56-year-old woman with breast cancer involving right humerus.
Diffusion-weighted imaging (DWI) performed in coronal plane with two different
techniques: echo-planar imaging (EPI) DWI (B) and
non–Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo
(SSFSE) DWI (C), both at b = 600 mm2/s, and corresponding,
respectively, apparent diffusion coefficient (ADC) maps (D and
E). Mean ADC (± SD) measured from humeral head is 1.07 ±
0.12 and 0.82 ± 0.17 x 10–3 mm2/s for
EPI and non-CPMG SSFSE DWI, respectively. These values are lower than those
measured in infectious process and avascular necrosis and reflect water
diffusion restriction by tumor cells.
|
|
View larger version (116K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 4E —56-year-old woman with breast cancer involving right humerus.
Diffusion-weighted imaging (DWI) performed in coronal plane with two different
techniques: echo-planar imaging (EPI) DWI (B) and
non–Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo
(SSFSE) DWI (C), both at b = 600 mm2/s, and corresponding,
respectively, apparent diffusion coefficient (ADC) maps (D and
E). Mean ADC (± SD) measured from humeral head is 1.07 ±
0.12 and 0.82 ± 0.17 x 10–3 mm2/s for
EPI and non-CPMG SSFSE DWI, respectively. These values are lower than those
measured in infectious process and avascular necrosis and reflect water
diffusion restriction by tumor cells.
|
|
Discussion
DWI measures the mobility of tissue water on a microscopic level and has
gained wide acceptance in the management of various CNS disorders. Several
potential fields of application, including the musculoskeletal system, bone
marrow, and abdominal organs, have also been reported in the medical
literature [3,
8,
15]. Because a relatively good
SNR can be achieved, EPI-based sequences are the most widely used DWI
techniques. Unfortunately, EPI-based DW images suffer from susceptibility
artifacts, chemical shift, and image distortion caused by eddy currents
resulting from large magnetic field gradients. To overcome the chemical shift
effect, EPI sequences are combined with fat saturation, which has a
detrimental effect on overall SNR. Hence, the use of EPI-based sequences for
DWI of the appendicular skeleton is limited
[3].
The need for artifact-free DWI has prompted research into other methods,
such as a single-shot DWI based on the rapid acquisition with relaxation
enhancement (RARE) sequence
[16]. A RARE acquisition
scheme uses a series of radiofrequency refocusing pulses rather than gradient
reversals to produce echo trains and therefore has a lower sensitivity to eddy
currents, chemical shift artifacts, and susceptibility gradients than the EPI
technique [13]. However, the
RARE method must obey the CPMG
[17] phase condition and, when
it is used with diffusion sensitization, cannot generate artifact-free images
due to uncontrolled phase modulations. The strong sensitivity of the sequence
to the CPMG condition can be suppressed but at the price of a reduction of the
SNR by a factor of 2 [18].
Le Roux [14] has addressed
this SNR loss in DWI by the use of a non-CPMG SSFSE technique. This new DWI
technique uses quadratic phase modulation of radiofrequency refocusing pulses
to generate a sustained train of stable echoes. This results in a DWI
technique that is less sensitive to eddy currents and magnetic field
inhomogeneities without any apparent signal loss. The non-CPMG SSFSE technique
has been recently used for DWI of the spine
[14,
19]. The decreased chemical
shift achieved with the non-CPMG SSFSE technique makes the use of fat
suppression unnecessary. In addition to the decreased image distortion and
decreased susceptibility artifacts, the non-CPMG SSFSE technique results in
higher-SNR and higher-quality images, as reflected in the visual image quality
scores. Together, these results suggest that the non-CPMG SSFSE technique can
be used to improve SNR in DWI of the appendicular skeleton.
ADC values of normal bone marrow measured with the two different techniques
were within the limits defined by previous studies
[20]. On the other hand, the
difference in the ADC measurements found between the two different DWI
techniques in this study is not surprising and, as previously addressed, the
increased SNR in the non-CPMG SSFSE technique might be suspected as being the
primary source of this difference
[19,
21,
22]. The non-CPMG technique
with its decreased levels of susceptibility-related artifacts and eddy
currents might better reflect the diffusion properties of the appendicular
skeleton. However, phantom studies or studies of larger patient populations
are needed to verify that statement.
Systemic and focal diseases, including infection, trauma, and neoplasia,
frequently affect the appendicular skeleton. Although conventional MRI has a
high sensitivity in detecting lesions, it has relatively limited specificity
in differentiating among their causes
[20]. In these settings, DWI
may be a helpful technique to outline the underlying process. Any pathologic
process, whether it is neoplastic, inflammatory, or degenerative, may disturb
normal tissue architecture and causes ultimate shifting of water molecules
between tissue compartments secondary to disruption of cellular structure,
membranous permeability, or both
[23].
The results of a few pioneering studies published in the literature reflect
the promising application of DWI in the differential diagnosis of skeletal
disorders, including posttraumatic edema, infection, metastases, and
degenerative changes [7,
19,
24–26].
Increased diffusion of interstitial water is a common phenomenon and may be
observed in acute posttraumatic edema of the bone resulting in low signal
intensity on DWI [25]. In
contrast, densely packed tumor cells restrict water diffusion, resulting in
lower phase shift with high signal intensity on DWI
[7]. However, these signal
intensity changes not only are related to diffusion alterations but also are
greatly influenced by the T2 shine-through effect.
To eliminate the T2 shine-through effect from DW images, a limited number
of studies have been completed using ADC mapping and measurements, but that
work has failed to show any significant difference in terms of ADC among
various bone marrow abnormalities
[7,
27]. However, those
quantitative studies used EPI-based DWI techniques, which are more sensitive
to eddy currents and susceptibility artifacts. These constraints might have
contributed to the failure to show ADC differences among various diseases.
Recently, the non-CPMG SSFSE DWI technique has been found to be promising in
the quantitative evaluation of various spinal diseases
[19]. Similarly, this
technique can easily be implemented as a promising tool in the imaging
evaluation of various disorders of the appendicular skeleton.
A second promising application of DWI of the appendicular skeleton can be
in determining the extent of bone involvement and predicting bone damage in
AVN. In a recent study, Menezes et al.
[28] evaluated diffusion
changes in femoral head ischemia on an animal model using a line-scan DWI
technique. They stated that in AVN of the femoral head, diffusion increases
early and remains elevated despite the reversal of the causative agent and
that, therefore, diffusion changes may be a better indicator of lasting
femoral head damage. In our study, ADC values of patients with AVN were found
to be higher than those of the other patient group and those with normal
vertebral bone marrow, which reflects the presence of interstitial edema
resulting in increased diffusion. This finding closely parallels the results
of Menezes et al. in their study of an animal model.
The line-scan DWI technique used by Menezes et al.
[28] is a
spin-echo–based method that produces fair image quality and little
susceptibility-related artifacts
[20,
28]. However, this sequence is
not commonly available, requires multiple signal averaging to compensate for
the relatively moderate SNR, can be time consuming with elaborate
postprocessing needed, and therefore has limited use to specialized centers
[20,
21]. On the other hand, the
non-CPMG SSFSE technique, with its good SNR and excellent image quality as
well as the fact that it requires only little postprocessing, is showing
promise for obtaining DW images of the appendicular skeleton where magnetic
field susceptibility effects are prominent.
A main limitation for our study is that only a small number of patients
with skeletal lesions were studied. Measured lesion CNR was found to be higher
on non-CPMG SSFSE DWI, reflecting improved lesion conspicuity. Compared with
an infectious process and AVN, metastases had lower ADC values. This finding
reflects an emphasized water restriction caused by the tumor packing. On the
other hand, ADC values of AVN and an infectious process showed considerable
overlap on both DWI techniques. However, it was not within the scope of this
study to draw conclusions regarding the capability of the non-CPMG SSFSE DWI
technique to differentiate among different skeletal diseases and disorders. To
address this important question, further studies with a larger cohort of
patients are needed in the future.
In conclusion, the non-CPMG SSFSE technique, with its reduced
susceptibility artifacts and increased SNR, provides a significant improvement
over the currently used EPI-based DWI technique and has the potential to be a
powerful tool in imaging the appendicular skeleton.
Acknowledgments
We are grateful to P. Le Roux, from the Global Applied Science Laboratory,
for his invaluable support and contribution in the achievement of this
study.
References
- Reddick WE, Bhargava R, Taylor JS, Meyer WH, Fletcher BD. Dynamic
contrast-enhanced MR imaging evaluation of osteosarcoma response to
neoadjuvant chemotherapy. J Magn Reson Imaging1996; 5:689
-694[CrossRef]
- Roberts TPL. Physiologic measurements by contrast-enhanced MR
imaging: expectations and limitations. J Magn Reson
Imaging 1997; 7:82
-90[Medline]
- Baur A, Reiser MF. Diffusion-weighted imaging of the
musculoskeletal system in humans. Skeletal Radiol2000; 29:555
-562[CrossRef][Medline]
- Schaefer PW, Grant PE, Gonzalez RG. Diffusion-weighted MR imaging
of the brain. Radiology 2000;217
: 331-345[Abstract/Free Full Text]
- Sorensen AG, Wu O, Copen WA, et al. Human acute cerebral ischemia:
detection of changes in water diffusion anisotropy by using MR imaging.
Radiology 1999;212
: 785-792[Abstract/Free Full Text]
- Tsuruda JS, Chew WM, Moseley ME, et al. Diffusion-weighted MR
imaging of extraaxial tumors. Magn Reson Med1991; 19:316
-320[Medline]
- Herneth AM, Philipp MO, Naude J, et al. Vertebral metastases:
assessment with apparent diffusion coefficient.
Radiology 2002;225
: 889-894[Abstract/Free Full Text]
- Baur A, Dietrich O, Reiser M. Diffusion-weighted imaging of bone
marrow: current status. Eur Radiol 2003;13
: 1699-1708[CrossRef][Medline]
- Hayashida Y, Yakurshiji T, Awai K, et al. Monitoring therapeutic
responses of primary bone tumors by diffusion-weighted image: initial results.
Eur Radiol 2006;16
: 2637-2643[CrossRef][Medline]
- Hayashida Y, Hirai T, Yakushiji T, et al. Evaluation of
diffusion-weighted imaging for the differential diagnosis of poorly
contrast-enhanced and T2-prolonged bone masses: initial experience.
J Magn Reson Imaging 2006;23
: 377-382[CrossRef][Medline]
- Turner R, LeBihan D. Single-shot diffusion imaging at 2.0 Tesla.
J Magn Reson 1990;86
: 445-452
- Pierpaoli C, Jezzard P, Basser PJ, et al. Diffusion tensor MR
imaging of the human brain. Radiology1996; 201:637
-648[Abstract/Free Full Text]
- Bastin ME, Le Roux P. On the application of a non-CPMG single-shot
fast spin-echo sequence to diffusion tensor MRI of the human brain.
Magn Reson Med 2002;48
: 6-14[CrossRef][Medline]
- Le Roux P. Non-CPMG fast spin echo with full signal. J
Magn Reson 2002; 155:278
-292[CrossRef][Medline]
- Chow LC, Bammer R, Moseley ME, et al. Single breath-hold
diffusion-weighted imaging of the abdomen. J Magn Reson
Imaging 2003; 18:377
-382[CrossRef][Medline]
- Hennig J, Nauerth A, Friedburg H. RARE imaging: a fast imaging
method for clinical MR. Magn Reson Med1986; 3:823
-833[Medline]
- Carr HY, Purcell EM. Effect of diffusion on free precession in
nuclear magnetic resonance experiments. Phys Rev1954; 94:630
-638[CrossRef]
- Norris DG, Bornert P, Reese T, et al. On the application of
ultra-fast RARE experiments. Magn Reson Med1992; 27:142
-164[Medline]
- Öner AY, Tali T, Celikyay F, Celik A, Le Roux P. Diffusion
weighted imaging of the spine with a non–Carr-Purcell-Meiboom-Gill
single-shot fast spin-echo sequence: initial experience. Am J
Neuroradiol 2007; 28:575
-580[Abstract/Free Full Text]
- Herneth AM, Friedrich K, Weidekamm C, et al. Diffusion weighted
imaging of bone marrow pathologies. Eur J Radiol2005; 55:74
-83[CrossRef][Medline]
- Bammer R, Herneth AM, Maier SE, Butts K, Prokesch RW. Line scan
diffusion imaging of the spine. Am J Neuroradiol2003; 24:5
-12[Abstract/Free Full Text]
- Zhou XJ, Leeds NE, McKinnon GC, et al. Characterization of benign
and metastatic vertebral compression fractures with quantitative diffusion MR
imaging. Am J Neuroradiol 2002;23
: 165-170[Abstract/Free Full Text]
- Bammer R. Basic principles of diffusion-weighted imaging.
Eur J Radiol 2003;45
: 169-184[CrossRef][Medline]
- Maeda M, Sakuma H, Maier SE, Takeda K. Quantitative assessment of
diffusion abnormalities in benign and malignant vertebral compression
fractures by line scan diffusion-weighted imaging. AJR2003; 181:1203
-1209[Abstract/Free Full Text]
- Spuentrup E, Buecker A, Adam G, van Vaals JJ, Guenther RW.
Diffusion-weighted MR imaging for differentiation of benign fracture edema and
tumor infiltration of the vertebral body. AJR2001; 176:351
-358[Abstract/Free Full Text]
- Baur A, Stabler A, Bruning R, et al. Diffusion-weighted MR imaging
of bone marrow: differentiation of benign versus pathologic compression
fractures. Radiology 1998;207
: 349-356[Abstract/Free Full Text]
- Pui MH, Mitha A, Rae WI, et al. Diffusion-weighted magnetic
resonance imaging of spinal infection and malignancy. J
Neuroimaging 2005; 15:164
-170[CrossRef][Medline]
- Menezes NM, Connolly SA, Shapiro F, et al. Early ischemia in
growing piglet skeleton: MR diffusion and perfusion imaging.
Radiology 2007;242
: 129-136[Abstract/Free Full Text]
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
Top
Abstract
Introduction
