AJR 2002; 179:187-192
© American Roentgen Ray Society
Contrast-Enhanced Magic-Angle MR Imaging of the Achilles Tendon
Helen Marshall1,
Clare Howarth,
David J. Larkman,
Amy H. Herlihy,
Angela Oatridge and
Graeme M. Bydder
1 All authors: Imaging Sciences Department, The Robert Steiner Magnetic
Resonance Unit, MRC Clinical Sciences Centre, Imperial College Faculty of
Medicine, Hammersmith Hospital, Du Cane Rd., London W12 0HS, England.
Received October 8, 2001;
accepted after revision January 14, 2002.
Supported by Diagnostic Investigations of Spinal Conditions and Sciatica,
the Arthritis Research Campaign, and Marconi Medical Systems.
Address correspondence to G. M. Bydder.
Abstract
OBJECTIVE. The objective of this study was to image the Achilles
tendon with MR imaging at the magic angle (the long axis of the tendon at
55° relative to the direction of the main static magnetic field
[B0]) to detect signal from the tendon, to measure the T1 of the
tendon, and to determine patterns of contrast enhancement in control subjects
and patients.
CONCLUSION. Mean T1 values of 311 ± 30 msec (at 1.0 T) were
found in six volunteers. In six control volunteers, slow uptake of contrast
material that dispersed over 40 min-1.5 hr was shown without focal change,
with elimination in most cases occurring within 18-24 hr. Small rapidly
enhancing focal areas of enhancement were seen next to the insertion of the
tendon and centrally within 5-10 min in two control volunteers. The focal
areas were located at the sites of the blood supply. A patient with chronic
tendinopathy showed early local contrast enhancement that extended widely
within the tendon over several hours. Two patients with a partially ruptured
or repaired tendon showed marked rapid contrast enhancement. The enhancement
was obvious with the tendon at the magic angle but was not evident with the
tendon in the usual orientation for MR examinations parallel to
B0.
Introduction
With conventional MR imaging pulse sequences and orientation parallel to
B0, the normal Achilles tendon usually has a low signal intensity
[1]. The low signal is a
consequence of strong dipolar interactions between ordered protons, which lead
to rapid loss of the MR imaging signal after excitation. This is manifest as a
very short T2 with little or no signal detectable with the TEs available on
most clinical systems.
Although the lack of detectable signal is an advantage for some diagnostic
purposes, it also means that it is not possible to detect effects due to
contrast agents in normal tendons because the tendon signal remains
undetectable even if its T1 or T2 is shortened by the contrast agent.
With in vitro studies, the T2s of tendons vary with orientation relative to
the static B0 field
[2,
3], and, in particular, T2 may
be increased when the tendon is placed at the magic angle (i.e., at 
=
55° relative to B0). The magnitude of the dissipative dipolar
interactions that lead to rapid signal loss is modulated by the term "3
cos2-1," which is equal to zero at 55°. The high
signal intensity produced in the tendon because of increases in T2 has
previously been recognized in clinical practice as an artifact
[4]. Steps have been taken to
avoid artifacts by placing the tendons parallel or perpendicular to
B0 and increasing the pulse sequence TE
[5]. Only recently has the
magic-angle effect been deliberately exploited for imaging purposes by placing
tendons at 55° relative to B0 to increase their T2s and to
allow the signal to be detected from them
[6].
We have studied a small group of volunteers and patients with their
Achilles tendon at the magic angle and used this technique to measure T1
values of the tendon and to study the effects of contrast enhancement in the
tendon over time.
Subjects and Methods
With the permission of the local research ethics committee and informed
consent from each subject, we studied eight control volunteers and three
patients with diseases of the Achilles tendon.
Two-dimensional multislice spin-echo (TR/TE, 500/16) and inversion recovery
(1500/16; inversion time, 300 msec) pulse sequences were used with a matrix of
192 x 256 and a slice thickness of 3 mm. A three-dimensional
radiofrequency spoiled gradient-echo image (21/6) with a flip angle of 35°
and an isotropic resolution of 1.6 mm was also obtained. Studies were
performed with a 1.0-T MR imaging system (Marconi Medical Systems, Cleveland,
OH). The subjects were examined in the lateral decubitis position with their
Achilles tendons oriented at 55° relative to B0 and placed at
the center of a 10-cm-diameter surface coil positioned in the system couch.
The ankle was dorsiflexed to 90° to place the Achilles tendon under some
tension, and the ball of the foot was placed against a rigid support to reduce
patient motion. For illustrative purposes, two volunteers also had these
sequences performed with their Achilles tendons at 0° relative to
B0.
Gadodiamide (0.3 mmol/kg) was administered by slow IV injection after the
first pulse sequence cycle. The cycle was repeated four times during the first
examination. When possible, the volunteers underwent further imaging (a single
cycle) approximately 8-18 hr and 20-36 hr after the initial contrast
injection. The spin-echo (1500/16) and inversion recovery (1500/16; inversion
time, 300 msec) pulse sequences were used to calculate T1 with a simplex
iterative root finding the algorithm. Three regions of interest were selected
for these calculations. The three patients had the initial five-cycle
examination followed by a cycle with their Achilles tendons oriented at 0°
relative to B0.
Results
The change in signal intensity due to the magic-angle effect is illustrated
in a control volunteer in Figure
1A,1B
using a spin-echo (1500/16) pulse sequence. No signal is apparent in the
tendon when it is orientated at 0° relative to B0
(Fig. 1A), but the signal is
obvious when it is placed at 55° relative to B0
(Fig. 1B).
Eight asymptomatic male volunteers (age range, 27-58 years) were studied.
The unenhanced T1 values of six volunteers are shown in
Table 1 (the other subjects had
images with artifacts) together with T1 values in the three patients.
Six volunteers showed generalized enhancement without focal features. This
enhancement was most apparent on the inversion recovery MR images, in which a
slow increase in signal intensity occurred over 40 min-1.5 hr, with a
subsequent decrease that was complete at 24 hr in all but one control subject.
Values of T1 computed from regions of interest placed centrally within the
tendon in these subjects and plotted against time are shown in Figure
2A,2B.
The large error bars seen in these measurements reflect tissue heterogeneity
in the region of interest rather than intrinsic uncertainty in T1. This is
shown by the clear trends seen in the data in the error bars.
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Fig. 2A. —Six male control volunteers between 27 and 45 years old.
Plots of T1 against time in Achilles tendon show decrease in T1 over 40
min-1.5 hr followed by return to normal values over 1-22 hr. Large error bars
seen in these measurements reflect tissue heterogeneity in region of interest
rather than intrinsic uncertainty in T1, which is shown by clear trends seen
in data.
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Fig. 2B. —Six male control volunteers between 27 and 45 years old.
Plots of T1 against time in Achilles tendon show decrease in T1 over 40
min—1.5 hr followed by return to normal values over 1-22 hr. Large error
bars seen in these measurements reflect tissue heterogeneity in region of
interest rather than intrinsic uncertainty in T1, which is shown by clear
trends seen in data.
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Two other control volunteers showed areas of focal enhancement that were
apparent on the first contrast-enhanced scans. The areas of focal enhancement
were central and close to the insertion of the tendon. The changes did not
diffuse widely in the tendon.
One control volunteer (who ran 20-25 miles [32-40 km] per week) was
subsequently clinically diagnosed with chronic tendinopathy. His sequential
scans showed uptake and dispersion of the contrast agent over time (Fig.
3A,3B,3C,3D,3E).
An initial enhancement peak was seen close to the myotendinous junction at 5
min, whereas maximum enhancement was seen centrally at 7 hr. T1 values for the
region located centrally and adjacent to the myotendinous junction are shown
in Figure 3E.
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Fig. 3A. —57-year-old man with chronic tendinopathy. Inversion recovery
MR images (TR/TE, 1500/16; inversion time, 300 msec) before (A), 5 min
after (B), 1 hr after (C), and 7 hr after (D)
administration of IV gadodiamide. Early enhancement is seen adjacent to
myotendinous junction and more centrally in B (arrows). This
enhancement diffuses more widely in C (arrows) and occupies
most of tendon in D (arrows).
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Fig. 3B. —57-year-old man with chronic tendinopathy. Inversion recovery
MR images (TR/TE, 1500/16; inversion time, 300 msec) before (A), 5 min
after (B), 1 hr after (C), and 7 hr after (D)
administration of IV gadodiamide. Early enhancement is seen adjacent to
myotendinous junction and more centrally in B (arrows). This
enhancement diffuses more widely in C (arrows) and occupies
most of tendon in D (arrows).
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Fig. 3C. —57-year-old man with chronic tendinopathy. Inversion recovery
MR images (TR/TE, 1500/16; inversion time, 300 msec) before (A), 5 min
after (B), 1 hr after (C), and 7 hr after (D)
administration of IV gadodiamide. Early enhancement is seen adjacent to
myotendinous junction and more centrally in B (arrows). This
enhancement diffuses more widely in C (arrows) and occupies
most of tendon in D (arrows).
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Fig. 3D. —57-yeard-old man with chronic tendinopathy. Inversion
recovery MR images (TR/TE, 1500/16; inversion time, 300 msec) before
(A), 5 min after (B), 1 hr after (C), and 7 hr after
(D) administration of IV gadodiamide. Early enhancement is seen
adjacent to myotendinous junction and more centrally in B
(arrows). This enhancement diffuses more widely in C
(arrows) and occupies most of tendon in D
(arrows).
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Fig. 3E. —57-year-old man with chronic tendinopathy. Plot of T1 versus
time shows myotendinous junction (region 1) and central area (region 2).
Myotendinous junction shows early uptake, whereas central area shows delayed
and lower uptake. Unenhanced inversion recovery sequence has low signal not
because of short T2 of tendon but because its inversion time is close to null
point.
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A partial rupture in an Achilles tendon 17 months after injury in a
34-year-old woman is shown in Figure
4A,4B,4C,4D.
Marked rapid uptake and elimination of contrast material took place over a
1-hr period. The contrast enhancement was obvious with the tendon at 55°
relative to B0 (Fig.
4B) but not with the tendon at 0° relative to B0
(Fig. 4C). The reduction in T1
(with the tendon imaged at 55° relative to B0) is shown in
Figure
4A,4B,4C,4D.
Similar findings were seen in a 42-year-old man who had suffered a partial
rupture of the tendon.
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Fig. 4B. —34-year-old woman with previous tendon rupture. Inversion
recovery sequence (1500/16; inversion time, 300 msec) at 55° is shown
after IV gadodiamide was administered. Note widespread enhancement in
thickened tendon (arrows).
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Fig. 4C. —34-year-old woman with previous tendon rupture. Inversion
recovery sequence (1500/16; inversion time, 300 msec) at 0° is shown after
IV gadodiamide was administered. This enhancement is not apparent with tendon
orientated at 0°.
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Discussion
This study shows that by positioning the Achilles tendon at the magic angle
of 55° relative to B0, it is possible to obtain signal from the
tendon, to measure the T1 of the tendon, and to show the uptake and
elimination of contrast material over time.
The T1 values measured in vivo in this study (311 ± 30 msec at 1.0
T) are longer than those of the in vitro bovine samples published by Fullerton
et al. [2] (163 ± 3 msec
at 0.25 T) but shorter than those obtained by Henkleman et al.
[3] (508 ± 30 msec at
1.5 T). The values obtained using a short TE technique
[7] are also shorter than those
obtained in three control human volunteers (490 ± 20 msec at 1.5 T).
The variations may reflect differences in field strength.
The pattern of contrast enhancement is of interest. To our knowledge, there
is no previous description of contrast enhancement in the normal Achilles
tendon, which may be because techniques used in this study, such as
triple-dose contrast enhancement, delayed studies, a highly T1-sensitive
inversion recovery sequence, and magic-angle imaging, increased the
sensitivity of MR imaging to contrast enhancement.
The early rapid uptake in small focal areas in two of the control
volunteers may reflect local blood supply in sites of known vascularity. The
slower, more generalized change in T1 in tendons probably reflects perfusion
and diffusion of the contrast agent into the tendon, with the gadodiamide
functioning as a monitor of solute transport. The blood supply of the Achilles
tendon comes from the muscle at its origin, the bone at its insertion, and the
paratenon. The tendon as a whole is relatively avascular with a more avascular
zone 2-6 cm from its insertion
[8,9,10],
and the slow normal uptake in the bulk of the tendon may reflect this low
level of perfusion and transport by diffusion. The pattern of contrast uptake
and retention may also depend on tendon proteoglycan content, because these
negatively charged molecules are associated with retention of water and
probably of gadodiamide. The results in the volunteer studies may reflect
differences in age and exercise status and subclinical degenerative change;
these factors should be controlled in future studies.
The rapid contrast enhancement in disease may be due to increased
vascularity as described in chronic tendonitis
[11]. The rapid elimination of
contrast material may be a consequence of reduced proteoglycan content in the
healing tendon. Although contrast enhancement has been shown to be useful in
the diagnosis of Achilles tendonosis
[12], routine clinical images
obtained at the conventional angle of 0° may underestimate the extent of
enhancement and thus the extent of disease.
The use of very short TEs (i.e., 0.228 msec) increases the signal
detectable from the Achilles tendon without placing it at the magic angle
[7]. However, this technique
may require higher performance hardware and specialized pulse sequences (such
as projection reconstruction and half pulse excitation), whereas placing the
tendon at 55° is achievable on most MR imaging systems, and no specialized
pulse sequences are required to detect signal from it.
Magic-angle imaging may allow a wide range of MR imaging techniques to be
applied to the study of tendons and ligaments throughout the body and may
provide new options to show contrast enhancement and other MR imaging
parameters in both health and disease.
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Abstract
Introduction
