DOI:10.2214/AJR.07.2548
AJR 2007; 189:1502-1509
© American Roentgen Ray Society
Early Rheumatoid Arthritis: A Review of MRI and Sonographic Findings
Nathalie Boutry1,
Mélanie Morel1,
René-Marc Flipo2,
Xavier Demondion1,3 and
Anne Cotten1
1 Department of Musculoskeletal Radiology, Centre Hospitalier Universitaire de
Lille and Hôpital Roger Salengro, CHRU de Lille, Blvd. du Pr. J
Leclercq, 59037 Lille, France.
2 Department of Rheumatology, Centre Hospitalier Universitaire de Lille and
Hôpital Roger Salengro, Lille, France.
3 Department of Anatomy, Centre Hospitalier Universitaire de Lille and
Hôpital Roger Salengro, Lille, France.
Received January 24, 2007;
accepted after revision June 19, 2007.
Address correspondence to N. Boutry
(nboutry{at}chru-lille.fr).
Abstract
OBJECTIVE. The introduction of anti–tumor necrosis factor
agents has opened new prospects in therapeutic management of patients
with early rheumatoid arthritis, thereby creating new demands on radiologists
to identify patients with aggressive disease at an early stage. As a result,
imaging techniques such as MRI and sonography have developed during the past
few years.
CONCLUSION. This article illustrates the imaging findings that may
be encountered with these techniques in patients with early rheumatoid
arthritis.
Keywords: extremities • hand • MRI • musculoskeletal imaging • power Doppler sonography • rheumatoid arthritis • sonography • wrist
Introduction
Rheumatoid arthritis is characterized by proliferative, hypervascularized
synovitis, resulting in bone erosion, cartilage damage, joint destruction, and
long-term disability. Diagnosis is based on clinical, laboratory, and
radiographic findings. Conventional radiography has been the mainstay for
diagnosis of joint damage and subsequent follow-up. Radiography can provide
only indirect information on synovial inflammation, however, and the technique
is insensitive to early bone damage. Until recently, the absence of effective
treatment to prevent joint destruction has limited the need for more sensitive
imaging techniques. This situation changed after the development of new
therapeutics for rheumatoid arthritis, such as the anti–tumor necrosis
factor (TNF) agents. Availability of these powerful and expensive
drugs has created new demands on radiologists to identify patients with
aggressive rheumatoid arthritis at an early stage to affect the therapeutic
management of these patients.
MRI and sonography can be useful tools in evaluating patients with early
rheumatoid arthritis. Both imaging techniques can detect preerosive synovitis.
They can also identify early bone damage before it becomes apparent on
radiography. Furthermore, MRI can be used to predict future bone damage.
Because MRI and sonography are rapidly becoming imaging techniques for the
evaluation of patients with early rheumatoid arthritis, the purpose of this
article is to illustrate how these techniques can be used in diagnosing early
stage rheumatoid arthritis, monitoring disease activity, and differentiating
early rheumatoid arthritis from other inflammatory arthritides in some
patients.
Positive Diagnosis of Early Rheumatoid Arthritis
The wrist and the metacarpophalangeal (MCP) and metatarsophalangeal (MTP)
joints are among the first areas to be affected in rheumatoid arthritis. The
most symptomatic extremity, the dominant extremity, or both may be studied
with MRI and sonography. Abnormalities in early rheumatoid arthritis include
synovitis, tenosynovitis, bone erosions, bone marrow edema, and bursitis.
Synovitis
Proliferative synovitis (i.e., rheumatoid pannus) is the earliest
pathologic abnormality in rheumatoid arthritis, and it is secondarily
responsible for bone and cartilage damage. It is usually, but not exclusively,
bilateral. MRI reveals proliferative synovitis as thickening of the synovial
membrane that appears as quick enhancement after the administration of
gadolinium [1]. This is well
shown on fat-suppressed gadolinium-enhanced T1-weighted images (Figs.
1A and
1B). Sonography shows abnormal
hypoechoic (relative to subdermal fat) intraarticular tissue that is poorly
compressible and that exhibits Doppler signal with color or power Doppler
imaging [2]
(Fig. 2).
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Fig. 1A —34-year-old woman with early rheumatoid arthritis and
synovitis. Transverse fat-suppressed gadolinium-enhanced T1-weighted spin-echo
MR images show bilateral synovitis (arrows) in wrist (A) and
metatarsophalangeal joints (B). Note also bone marrow signal intensity
changes (asterisks, B), which precede frank bone erosions, and
flexor digitorum tenosynovitis (arrowhead, A).
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Fig. 1B —34-year-old woman with early rheumatoid arthritis and
synovitis. Transverse fat-suppressed gadolinium-enhanced T1-weighted spin-echo
MR images show bilateral synovitis (arrows) in wrist (A) and
metatarsophalangeal joints (B). Note also bone marrow signal intensity
changes (asterisks, B), which precede frank bone erosions, and
flexor digitorum tenosynovitis (arrowhead, A).
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Fig. 2 —41-year-old man with early rheumatoid arthritis and
synovitis. Dorsal longitudinal color sonogram of wrist reveals hypoechoic
distention of both radiocarpal (single asterisk) and midcarpal
(double asterisks) synovial recesses. High signal in synovium on
power Doppler imaging indicates hyperemia. R = radius, L = lunate, C =
capitate.
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A small amount of fluid may be associated with synovitis. This fluid shows
high signal intensity on T2-weighted MR images and low signal intensity on
fat-suppressed gadolinium-enhanced T1-weighted MR images. The fluid appears
anechoic on sonography, with no evidence of flow on Doppler imaging, and can
be expelled from the region by compression with the sonographic transducer.
Both MRI and sonography are more sensitive than clinical assessment for
detecting synovial inflammation
[3], and they help distinguish
between patients with polyarthritis and those with oligoarthritis.
Conventional radiography, on the other hand, is not helpful in the
diagnosis of synovitis unless there is fusiform soft-tissue swelling at the
joints. This swelling is well seen at the proximal interphalangeal joints and,
to a lesser extent, at the MCP joints.
Tenosynovitis
Tenosynovitis is a common finding in patients with early rheumatoid
arthritis. Although any tendon may be affected, the flexor digitorum, extensor
digitorum, and extensor carpi ulnaris are frequently involved
[4]. Tenosynovitis is usually,
but not exclusively, bilateral. MRI reveals thickening of the synovial sheath
with marked enhancement on fat-suppressed gadolinium-enhanced T1-weighted
images [4]
(Fig. 3A). Sonography shows
similar findings: hypoechoic thickening of the synovial sheath with hyperemia
on Doppler imaging [2]
(Fig. 3B).
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Fig. 3A —29-year-old woman with early rheumatoid arthritis and
tenosynovitis. R = radius, U = ulna, t = tendon. Transverse fat-suppressed
gadolinium-enhanced T1-weighted spin-echo MR image shows significant
enhancement (arrows) around extensor carpi ulnaris tendon that
represents tenosynovitis. Note also mild enhancement in distal radioulnar
joint, which is suggestive of synovitis.
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Fig. 3B —29-year-old woman with early rheumatoid arthritis and
tenosynovitis. R = radius, U = ulna, t = tendon. Dorsal transverse sonogram of
wrist shows hypoechoic thickening (asterisks) and hyperemia around
extensor carpi ulnaris tendon on power Doppler imaging, representing
tenosynovitis. Note also heterogeneous appearance of tendon on sonography.
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A small amount of fluid may be associated with tenosynovitis. In some
patients with early rheumatoid arthritis, affected tendons may appear
heterogeneous (suggesting incipient tendinitis) on both imaging techniques.
These tendinous changes are seen best on sonography
(Fig. 3B). Both MRI and
sonography outperform conventional radiography in detecting tenosynovitis.
Bone Erosions
Bone erosions result from proliferative synovitis. They are less frequently
bilateral than synovitis or tenosynovitis. The capitate, triquetrum, and
lunate bones (Fig. 4A); the
radial aspect of the second and third metacarpal bones
(Fig. 4B); and the lateral
aspect of the fifth metatarsal bone (Fig.
4C) are more frequently involved with bone erosions
[4,
5]. On MRI, bone erosions
appear as sharply marginated areas of trabecular bone loss with a cortical
defect [1], often associated
with synovitis. These erosions are well seen after IV gadolinium injection,
especially with thin-partition 3D gradient-echo sequences
[4] (Figs.
4A,
4B, and
4C).
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Fig. 4A —38-year-old woman with early rheumatoid arthritis and bone
erosions. Transverse fat-suppressed gadolinium-enhanced 3D gradient-echo MR
image reveals carpal bone erosions (capitate, triquetrum, pisiform)
(arrows). Synovitis in carpal joints and flexor and extensor
tenosynovitis are also evident. (Reprinted with permission from Boutry N,
Larde A, Lapegue F, Solau-Gervais E, Flipo RM, Cotten A. Magnetic resonance
imaging appearance of the hands and feet in patients with early rheumatoid
arthritis. J Rheumatol 2003; 30:671–679
[4])
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Fig. 4B —38-year-old woman with early rheumatoid arthritis and bone
erosions. Transverse fat-suppressed gadolinium-enhanced 3D gradient-echo MR
image shows bone erosion on radial aspect of third metacarpal bone
(arrowhead). Note also presence of significant bilateral synovitis in
second and third metacarpophalangeal joints and flexor digitorum tenosynovitis
(arrows).
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Fig. 4C —38-year-old woman with early rheumatoid arthritis and bone
erosions. Transverse fat-suppressed gadolinium-enhanced 3D gradient-echo MR
image exhibits bone erosion on lateral aspect of fifth metatarsal bone
(arrowhead), which is associated with synovitis. Note also presence
of inflammatory bursitis beneath fifth metatarsal bone (asterisk).
(Reprinted with permission from Boutry N, Larde A, Lapegue F, Solau-Gervais E,
Flipo RM, Cotten A. Magnetic resonance imaging appearance of the hands and
feet in patients with early rheumatoid arthritis. J Rheumatol 2003;
30:671–679 [4])
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On sonography, bone erosions are seen as intraarticular discontinuities of
the bone surface that are visible in two perpendicular planes
[2]. They are best detected at
the ulnar styloid process (Fig.
5A), the radial aspect of the second MCP joint, the ulnar aspect
of the fifth MCP joint, and the lateral aspect of the fifth MTP joint
[4]
(Fig. 5B). High signal on
Doppler imaging suggests the presence of proliferative, hypervascularized
pannus tissue in the erosion
[2]
(Fig. 5C). Compared with MRI,
however, sonography is limited in the evaluation of the other MCP and MTP
joints—because of limitations of probe positioning, even with a
"hockey stick" transducer—and the carpal bones. MRI is more
sensitive than conventional radiography for diagnosing bone erosions
[6]. The same is true of
sonography for the MCP and MTP joints
[7,
8].
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Fig. 5A —47-year-old woman with rheumatoid arthritis and bone
erosions. Transverse sonogram of wrist exhibits bone erosion of ulnar styloid
process (arrow). Latter is related to hypoechoic thickening around
extensor carpi ulnaris tendon, representing tenosynovitis
(asterisks). U = ulna, t = tendon.
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Fig. 5B —47-year-old woman with rheumatoid arthritis and bone
erosions. Coronal sonogram of forefoot shows bone erosion (arrow) on
lateral aspect of fifth metatarsal bone (M5) associated with synovitis
(asterisks).
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Fig. 5C —47-year-old woman with rheumatoid arthritis and bone
erosions. Coronal sonogram of hand shows hypervascular pannus filling bone
erosion (arrows) on radial aspect of second metacarpal bone (M2) on
power Doppler imaging. Note also hyperemia in articular space.
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Bone Marrow Edema
Bone marrow edema may precede the development of bone erosions and can be
used to predict medium-term functional disability
[9]. It is detectable with STIR
T2-weighted or fat-suppressed T2-weighted MRI sequences
(Fig. 6). Bone marrow edema
appears as a lesion with ill-defined margins and high signal intensity
[1], typically located at the
insertion of the synovial membrane. It can occur alone, or it may surround
bone erosions [1]. In contrast
to MRI, sonography provides no information on bone marrow edema.
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Fig. 6 —33-year-old man with early rheumatoid arthritis and bone
marrow edema. Coronal STIR T2-weighted MR image reveals bone marrow edema in
second metacarpal bone (asterisk). Note also fluid in articular
space.
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Bursitis
Bursitis is a common finding in patients with early rheumatoid arthritis
and may be asymptomatic. It is located between or beneath the metatarsal heads
[4]. Intermetatarsal and
submetatarsal bursitis show significant enhancement on MRI after IV gadolinium
injection due to inflammation (Fig.
7). On sonography, intermetatarsal and submetatarsal bursitis
appear as heterogeneous (hypo- and hyperechoic) collections that can be well-
or ill-defined (Fig. 8).
Significant hyperemia of the synovial lining is usually seen on Doppler
sonography (Fig. 8).
Intermetatarsal bursitis is more frequent in the second and third web spaces
[4], where it may be difficult
to differentiate from Morton's neuroma. However, location at the plantar
aspect of the foot on MRI and identification of the entering and exiting nerve
on sonography are more suggestive of interdigital nerve entrapment.
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Fig. 7 —51-year-old man with early rheumatoid arthritis and bursitis.
Transverse fat-suppressed gadolinium-enhanced 3D gradient-echo MR image shows
submetatarsal (asterisk) and intermetatarsal (boxes)
bursitis. Note also presence of bone erosion (arrow) associated with
synovitis in third metatarsophalangeal joint.
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Fig. 8 —28-year-old man with early rheumatoid arthritis and bursitis.
Longitudinal sonogram of web space reveals intermetatarsal bursitis
(asterisks) as well-defined heterogeneous collection with synovial
hyperemia on power Doppler imaging. (Courtesy of Morvan G, Paris, France)
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Disease Activity and Damage Monitoring
MRI and sonography are both useful in assessing early rheumatoid arthritis
activity. Modern drug therapies have reportedly decreased synovial
proliferation and bone marrow edema and prevented the development of bone
erosions. MRI and sonography can both quantify synovial inflammation.
Treatment response can be identified on MRI as a reduction in synovial volume
and a decrease in the rate of synovial enhancement
[10,
11]
(Fig. 9). Similarly,
sonography shows a decrease in synovial thickness and disappearance of the
Doppler signal in patients who respond to treatment
[12]. Microbubble sonographic
contrast agents may also improve the detection of synovial vascularization,
which is a marker of disease activity
[13], but they are not widely
used in daily practice.
More recently, methods of semiquantitative scoring of early rheumatoid
arthritis changes (i.e., synovitis, bone erosions, and bone edema) at the
wrist and MCP joints have been developed and standardized on MRI by the
OMERACT (Outcome Measures in Rheumatology Clinical Trials)
[1] and EULAR (European League
Against Rheumatism) [1] groups.
These scoring systems may also be useful in assessing rheumatoid arthritis
activity and bone damage.
Differential Diagnosis
Diagnosis of early rheumatoid arthritis is often based primarily on
inflammatory polyarthralgia of the hands. Clinicians sometimes struggle to
differentiate early rheumatoid arthritis from psoriatic arthritis or systemic
lupus erythematosus, especially when conventional radiography shows no
abnormality.
In patients with psoriatic arthritis, MRI may show extensive signal
intensity changes in the bone marrow on STIR T2-weighted, fat-suppressed
T2-weighted, or fat-suppressed gadolinium-enhanced T1-weighted sequences
[14]. These changes may
sometimes be seen in the soft tissues as well
[14]. Bone marrow changes due
to psoriatic arthritis do not remain localized in the joint capsule (in
contrast to those due to early rheumatoid arthritis) and can extend far beyond
the joint capsule, probably related to inflammatory enthesitis
(Fig. 10A).
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Fig. 10A —31-year-old man with psoriatic arthritis. Coronal
fat-suppressed T2-weighted MR image shows edematous signal intensity changes
(asterisks) in bone marrow of first phalanx. Note also similar
findings along collateral ligaments (arrows) of adjacent proximal
interphalangeal joint.
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Sonography cannot detect bone marrow changes, but it may exhibit signs of
peripheral enthesitis affecting the lower limbs (especially the Achilles
tendon and the plantar fascia) (Fig.
10B) and, in some cases, the fingers
(Fig. 10C). Enthesitis appears
as a hypoechoic thickening of the enthesis, associated with hyperemia on
Doppler imaging (Fig.
10C).
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Fig. 10B —31-year-old man with psoriatic arthritis. Longitudinal
sonogram of foot using extended field of view reveals enthesitis of plantar
fascia. Note significant hypoechoic thickening of fascia origin (double
arrow); also note bone erosions and spurs (arrowheads). More
distally, plantar fascia shows normal sonographic appearance
(arrows). C = calcaneus.
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Fig. 10C —31-year-old man with psoriatic arthritis. Coronal color
sonogram of hand shows enthesitis of radial collateral ligament as hypoechoic
thickening of ligament with mild hyperemia on power Doppler imaging. For
comparison, note normal fibrillar hyperechoic appearance of radial collateral
ligament on normal side (arrows). P1 = proximal phalanx, P2 = middle
phalanx.
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In patients with systemic lupus erythematosus, MRI may show abnormalities
similar to those of patients with early rheumatoid arthritis (e.g., synovitis,
tenosynovitis, and bone erosions), and it might be impossible to differentiate
patients with early rheumatoid arthritis from those with systemic lupus
erythematosus on MRI [15]
(Fig. 11).
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Fig. 11 —27-year-old woman with systemic lupus erythematosus.
Transverse fat-suppressed gadolinium-enhanced T1-weighted spin-echo MR image
shows bilateral synovitis in metacarpophalangeal joints and tenosynovitis
(arrows) in flexor and extensor digitorum, as well as bone erosion on
radial aspect of second metacarpal bone (arrowhead). MRI findings are
similar to those of early rheumatoid arthritis.
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Conclusion
MRI and sonography have opened new horizons in the detection of early joint
damage, assessment of synovial inflammation, and therapeutic management of
patients with rheumatoid arthritis. Radiologists should be familiar with the
MRI and sonographic appearances of early rheumatoid arthritis in the small
synovial joints of the appendicular skeleton. It is still too early to
indicate with certainty the role of imaging in treatment decisions. No
strategy has yet been proposed in the literature. However, sonography is a
quick and inexpensive way to detect synovitis, whereas MRI allows a more
global approach to the small synovial joints of the appendicular skeleton.
References
- Ostergaard M, Peterfy C, Conaghan P, et al. OMERACT Rheumatoid
Arthritis Magnetic Resonance Imaging Studies. Core set of MRI acquisitions,
joint pathology definitions, and the OMERACT RA-MRI scoring system.
J Rheumatol 2003;30
: 1385-1386 [Erratum in
J Rheumatol 2004; 31:198][Medline]
- Wakefield RJ, Balint PV, Szkudlarek M, et al. Musculoskeletal
ultrasound including definitions for ultrasonographic pathology. J
Rheumatol 2005; 32:2485
-2487[Abstract/Free Full Text]
- Backhaus M, Kamradt T, Sandrock D, et al. Arthritis of the finger
joints: a comprehensive approach comparing conventional radiography,
scintigraphy, ultrasound, and contrast-enhanced magnetic resonance imaging.
Arthritis Rheum 1999;42
: 1232-1245[CrossRef][Medline]
- Boutry N, Larde A, Lapegue F, Solau-Gervais E, Flipo RM, Cotten A.
Magnetic resonance imaging appearance of the hands and feet in patients with
early rheumatoid arthritis. J Rheumatol2003; 30:671
-679[Abstract/Free Full Text]
- McQueen FM, Stewart N, Crabbe J, et al. Magnetic resonance imaging
of the wrist in early rheumatoid arthritis reveals a high prevalence of
erosion at four months after symptom onset. Ann Rheum
Dis 1998; 57:350
-356[Abstract/Free Full Text]
- Foley-Nolan D, Stack JP, Ryan M, et al. Magnetic resonance imaging
in the assessment of rheumatoid arthritis: a comparison with plain film
radiographs. Br J Rheumatol 1991;30
: 101-106[Abstract/Free Full Text]
- Wakefield RJ, Gibbon WW, Conaghan PG, et al. The value of
sonography in the detection of bone erosions in patients with rheumatoid
arthritis: a comparison with conventional radiography. Arthritis
Rheum 2000; 43:2762
-2770[CrossRef][Medline]
- Szkudlarek M, Narvestad E, Klarlund M, et al. Ultrasonography of
the metatarsophalangeal joints in rheumatoid arthritis: comparison with
magnetic resonance imaging, conventional radiography, and clinical
examination. Arthritis Rheum 2004;50
: 2103-2112[CrossRef][Medline]
- Benton N, Stewart N, Crabbe J, et al. MRI of the wrist in early
rheumatoid arthritis can be used to predict functional outcome at 6 years.
Ann Rheum Dis 2004;63
: 555-561[Abstract/Free Full Text]
- Jevtic V, Watt I, Rozman B, et al. Contrast-enhanced Gd-DTPA
magnetic resonance imaging in the evaluation of rheumatoid arthritis during a
clinical trial with DMARDs: a prospective two-year follow-up study on hand
joints in 31 patients. Clin Exp Rheumatol1997; 15:151
-156[Medline]
- Ostergaard M, Hansen M, Stoltenberg M, et al. Magnetic resonance
imaging–determined synovial membrane volume as a marker of disease
activity and a predictor of progressive joint destruction in the wrists of
patients with rheumatoid arthritis. Arthritis Rheum1999; 42:918
-929[CrossRef][Medline]
- Ribbens C, Andre B, Marcelis S, et al. Rheumatoid hand joint
synovitis: gray-scale and power Doppler US quantifications following
anti-tumor necrosis factor-alpha treatment: pilot study.
Radiology 2003;229
: 562-569[Abstract/Free Full Text]
- Klauser A, Frauscher F, Schirmer M, et al. The value of
contrast-enhanced color Doppler ultrasound in the detection of vascularization
of finger joints in patients with rheumatoid arthritis. Arthritis
Rheum 2002; 46:647
-653[CrossRef][Medline]
- Jevtic V, Watt I, Rozman B, et al. Distinctive radiological
features of small hand joints in rheumatoid arthritis and seronegative
spondylo-arthritis demonstrated by contrast-enhanced (Gd-DTPA) magnetic
resonance imaging. Skeletal Radiol 1995;24
: 351-355[Medline]
- Boutry N, Hachulla E, Flipo RM, Cortet B, Cotten A. MR imaging
findings in hands in early rheumatoid arthritis: comparison with those in
systemic lupus erythematosus and primary Sjögren syndrome.
Radiology 2005;236
: 593-600[Abstract/Free Full Text]
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Abstract
Introduction
t, where SIt is signal
intensity obtained t seconds after contrast injection,
SI0 is signal intensity obtained in first unenhanced
image, and