Technical Innovation MR Imaging ofArticular Cartilage ...

Technical MR Imaging ofArticular Methods Using UkrashortTEs

Cartilage

of the

Garry E. Gold1, Daniel R. Thedens2, John M. Pauly2, Klaus R Fechner3, Gabrielle

T

he T2 relaxation decreases

out

of cartilage and

calci-

fled zones near the bone-cartilage [1, 2]. T2 relaxation times in these

interface zones

time

in the radial

can

10 msec

be

all zones

or less [1, 2]. Through-

of

cartilage,

short T2 relaxation

times

components

with

may be important

in

early detection of cartilage abnormalities [3]. We have developed two methods for highresolution,

ultrashort

cartilage. scopic

data

The second space (3D)

TE imaging

The first technique

spectro-

with high-resolution images. technique uses a non-Cartesian K-

along

trajectory image

of articular

acquires

to acquire

in about

a three-dimensional

5 mm.

Both

ultrashort TEs (to obtain signal the short-T2 components of

methods intensity cartilage)

use from and

shift artispectro-

lipid suppression to avoid chemical facts. The pmjection-reconstruction

scopic imaging (PRSI) technique is best suited for further evaluation of a focal region of cartilage abnormality. quence is useful entire joint

knee

whereas the 3D cone seeither for a survey of the

or for high-resolution

imaging

of a

compartment.

Materials Rationale

and

Methods

and Theory

PRSI.-The projection-reconstniction method used here has been applied to study atherosclerotic

Bergman1,

plaques [4] and tendons and menisci [5]. We used cither a half-pulse excitation, in which two excitations are combined to form a slice [4], or a conventional excitation

pulse.

The excitation

is immediately

fol-

lowed by pmjection-reconstruction spectroscopic readout gradients. After excitation, an oscillating readout gradient repeatedly scans one diameter in Kspace. This diameter rotates through 2it radians over the course of the scan, covering an entire cylinder in kk,s space. Increasing time delays are used to fill in the spectroscopic data. Reconstruction of the resultant PRSI data set uses a gridding algorithm [61. The size of the data set is 33 MB per slice. Reconstruction took approximately 6 mm per slice on an U1traSPARC workstation (Sun Microsystems, Mountain View, CA). Three-dimensional cones-The 3D cone imaging sequence is based on a non-Cartesian cone Kspace

trajectory

[7].

The

design

is similar

to a 3D

more efficient in 3D K-space coverage. A series of nested cones is overlaid with interleaved spirals. resulting in spiral readouts in the ks-k., plane and sinusoidal readouts in the k5-k and k-k planes. The 3D cone sequence provides isotropic resolution in all three dimensions. Because readout began from the center of K-space, an ultrashort ‘FE was possible (Thedens DR et al., presented at the International Society for Magnetic Resonance in Medicine meeting. April 1996). The 3D cone method used either chemical saturation to reduce lipid signal intensity or a spectrally and spatially selective excitation [8, 9]. A gridding algorithm [6] is used for reconstruction of the 3D cone data set. Reconstruction of the projection-reconstruction

technique

Innovation

but

Knee:

Christopher

12-MB

data

New

F. Beaulieu1, Albert Macovski2

set took 6 rain on an U1traSPARC

workstation. Patient

Information

Ten healthy volunteers and 10 patients with knee cartilage damage were examined. Patients with cartilage damage were recruited from a group under

consideration

for

autologous

chondrocyte

All scans were obtained with version 5.5 software on 1.5-1 Signa whole-body imaging systems (General Electric Medical Systems, Milwaukee, WI) using either the extremity coil for the whole-knee images or the 3-inch (7.6-cm) surface coil for images of the patellofemoral joint. Four scans were obtained for each healthy volunteer: PRSI, half-pulse excitation, TB = 200 psec; PRSI, conventional excitation, TE = 1.6 msec; 3D cone, chemical saturation, TE = 0.6 msec; and 3D cone, spectral-spatial excitation, TB = 6.6 msec. Three scans were obtained for each patient: 3D fat-suppressed gradient-recalled echo (3D-FSGRE), TB = 12 msec; PRSI, half-pulse excitation, TB = 200 Jisec; and PRSI, conventional excitation, TE= 1.6msec. transplantation.

Imaging Techniques

3D-FS-GRE.-The 3D-FS-GRE scan was performed on the high-speed gradient system with a maximum gradient amplitude of 2.2 G/cm and a maximum slew rate of 12 0/cm . jp1 ‘fl 3j.. FS-GRE technique used a field ofview (FOV) of 16 cm, with a512 x l92matrix and a2-mm slice thickness. TRIFE was 50/12 msec, and imaging time was 6 mm for 28 sections. The flip angle was 20g.

Received March 13, 1997; accepted after revision October 20, 1997. Presented atthe annual meeting ofthe American Roentgen Ray Society. Boston, May 1997. Winner ofthe President’s Award. 1 Department of Radiology, Stanford University, Stanford, CA 94305-5488.Address correspondence to 6. E. Gold. 2Department of Electrical Engineering, Stanford University, Stanford. CA 94305.

3VA Health Care System of Palo Alto, Stanford, CA 94305. AJR1998;170:1223-1226

AJR:170, May 1998

0361-803X198/1705-1223

©American

Roentgen Ray Society

1223

Gold

PRSI.-The PRSI technique was implemented on the high-speed gradient system with a maximum gradient amplitude of 2.2 G/cm and maximum slew rate of I 2 G/cm . msec’ . The PRSI technique used a minimum FOV of 6 cm, with an in-plane spatial resolution of 184 pm. Four interleaves were used to obtain spectroscopic data. Spectral resolution was 63 Hz (1.0 ppm), with a spectral bandwidth of 667 Hz (12.2 ppm). With a TR of 60 msec, imaging time is 4 mm per slice for the conventional excitation (TE = 1.6 msec, 2-mm slice thickness) and 8 mm per slice for the halfpulse excitation (TE = 200 psec, 3-mm slice thickness). The flip angle was 15#{176}. Three-dimensional cone.-The 3D cone technique was implemented on the standard gradient system with a maximum gradient amplitude of 2.0 G/cm and maximum slew rate of I .6 Gkm . msec. The 3D cone technique used a 12.8-cm FOV and a 1.0-mm isotropic resolution for the entire knee, which took 5.1 mm with a TR of 70 msec. A highresolution compartment survey 3D cone scan with 05-mm isotropic resolution and a 6.4-cm FOV took 9.7 mm with a TR of 70 msec. The flip angle was 20#{176}. Chemical saturation was used to reduce lipid signal intensity (TE = 600 lisec)or a spectrally and spatially selective excitation (TE = 6.6 msec). The spectral-spatial excitation was also used to restrict the FOV in one direction.

et al.

Results

the spectra

Images of healthy volunteers showed that PRSI technique can obtain high-resolution

face are also broader maximum), indicating

images

times

of the

patellofemoral

with

the half-pulse

obtained 200

isec,

3-mm

slice

creased signal-to-noise with the conventional msec,

2-mm

frequencies

cal shift

artifacts

Acquisition

the

PRSI

Images

thickness)

thickness).

allowed

data

set with

display

of im-

frequency. images

Water(Fig. from the pa-

cartilage

were

of the same

data

so no additional

ning

was required. was basis.

zones

of healthy

structed

Spectra

at the

tamed. Spectra cartilage-bone

acquired

scan-

from articular

water

voxels

across

cartilage,

frequency,

from the cartilage interface show lower

using time

of 1 mm. was

ob-

near the peak ar-

eas than spectra from the area closer to the joint surface (Fig. IB). The line widths on

cone images of the envolunteers were acquired coil and an isotropic TE was 600

5. 1 mm

(Figs.

psec,

2A and

resscan

and 2B).

Con-

trast was seen between articular cartilage adjacent bone, but poorer contrast was between

and muscle.

cartilage

Some

and seen

blurring

of the margins of the cartilage was seen. Reformation into either the sagittal (Fig. 2A) or the coronal The

(Fig.

2B) planes

3D cone

technique

high-resolution

obtain lofemoral

the

inter-

(full width at half peak shorter T2 relaxation

regions.

the extremity

olution

and

reconwere

in those

to the cartilage-bone

Three-dimensional tire joint of healthy

as part

In addition, spectroscopic available on a voxel-by-

information

voxel

all

no chemi-

tellofemoral

set,

in-

Because

occurred. of a full spectral

ages at any spectral 1A) and lipid-frequency

=

compared (TE = I .6

are resolved,

technique

(TE show

ratio when excitation

slice

spectral

joint. excitation

closer

cm FOV Images

images

ofhealthy

joint

2D). These

data

were

and the 3-inch were

reformatted

such as axial (Fig.

was performed. was

also

used

of the

volunteers

(Figs.

acquired (7.6-cm)

using surface

into standard

2C) and sagittal

to

paid2C a 6coil. planes,

(Fig.

2D).

was 600 psec, and scan time was 9.7 mm. Isotropic resolution was 0.5 mm.

TE

eas

Patient images (Figs. of cartilage damage

3 and 4) showing arwere acquired with

Fig. 1.-Axial MR images of patellofemoral joint of 25-year-old healthy volunteer using projection-reconstruction spectroscopic imaging sequence (TE = 200 isec). A, Water-frequency image. B, Magnified image of articular cartilage from box in A, along with spectra of patellofemoral cartilage. Note decreasing line width and increasing peak area as voxels progress from cartilage-bone interface to articular surface.

Fig. 2.-MR images of articular cartilage of knee of 24-year-old healthy volunteer using three-dimensional cone technique. A, Sagittal image with isotropic 1-mm resolution (field of view [FOV] = 12.8 cm, TE = 600 psec, scan time = 5.1 mm). B, Coronal image from same data set as A. C, Axial high-resolution image of patellofemoral joint with isotropic 0.5-mm resolution (FOV = 6.4 cm, TE = 600 psec, scan time D, Sagittal image from same data set as C.

1224

=

9.7 mm).

AJR:170, May 1998

MR Fig. 3.-Sagittal

of Articular

Cartilage

of the

Knee

MR image of knee of 30-year-old pacompartment

tient with medial (arrows). A, Fat-suppressed called echo image

cartilage

three-dimensional (TE 12 msec).

B, Projection-reconstruction frequency

Imaging

image

damage gradient-re-

spectroscopic

of same slice (TE

=

water-

1.6 msec).

#{149}..:,;*rtr

,

.

.

.

.

,-

( 4”

Fig. 4.-Sagittal MR image of knee of 39-year-old patient who had osteochondral drilling procedure 18 months previously. Medial-compartment cartilage damage (arrows) is seen. A, Fat-suppressed three-dimensional gradient-recalled echo image (TE = 12 msec). B, Projection-reconstruction spectroscopic waterfrequency image of same slice (TE = 1.6 msec).

the

PRSI

technique

using

the

extremity

Image

coil.

These tients

areas were well shown on all the pastudied, and spectra from these areas

were

available

fluid

was

intense

for

seen

Adjacent

as isointense

with

compared

on these

analysis.

joint

or slightly

not

hyper-

the articular

ideal

PRSI

cartilage

images.

contrast

when

will

A recent by

sensitivity

study

of patellar

Brossmann

cartilage

et al.

[3]

of an ultrashort-TE

construction

imaging

suppressed

spoiled

speci-

compared

3D fatecho

with

sequence

gradient-recalled

better

niques. lieved

This improved to be due to

associated short

T2

with

did

collagen

relaxation

and 3D cone ages

than

time

techniques

of cartilage

AJR:170, May 1998

with

two

delineation detection

was beof water which

[3]. Both produce

similar

tech-

has

the PRSI in vivo

ultrashort

imTEs.

because intensity

RF

synovial

which

from

on

of RF contrast

will

subject

of future

spoiling

than

water

content

to

[

study.

(Gold

nance

in Medicine current

PRSI

existing

cartilage

sequence

defects.

evaluation

T2 relaxation

has

techniques The

of cartilage

times.

several

in the ultrashort components

The

advantages

evaluation TE with

use of spectral

of

allows

not

limited

face

coil

interface.

et al., for

meeting.

resolution

by or

an

a data 6

can he acquired

Reso-

or at

improved

antialiasing coil

at the

1996)

April

capacity.

extremity

per

at lower

presented

The filter.

is

FOV to prevent aliasing. A limited number of slices

strict

pro-

mm

Magnetic

with

and processing

re-

inhomoge-

and

approximately

GE

injury

readout

requires

Society

of

be important

cartilage

artifacts

slices

International

storage

The

over

of

Multiple

resolution

1 11

of early

technique

time

line

(51. Estimation

spectroscopic shift

a very

a broader

area could

sites The

PRSI

to have

and

cartilage

by peak

spe-

For example,

shown

at the cartilage-bone

The

slice.

PRS!

a

hyaline

characterize

detects. time

chemical

cessing

or mag-

subtraction

help

been

relaxation

edema.

neity

In addi-

of the T2 decay of cartilage during the spectroscopic

transfer

width

solves

relative

has

T2

and

long-Tl

[10]. PRSI

fibrocartilage short

in determining

echo

spoiling,

fluid

bright

netization be the

the 3D

and line widths could cific areas of cartilage

the

the other

fiber,

as

The

unlike

intensity

appears

present.

gradient-recalled

have

The addition

readout.

and magnetization transfer contrast subtraction MR imaging. The projection-reconstruction imaging technique delineated cartilage lesions

such

cartilage signal

not signal

fluid

tion,

projection-re-

and the 3D

is

sequences.

spoiled

do

reduce

species

the

the PRSI

effusion

and 3D cone

methods,

mens

an

fat-suppressed

Discussion

with

cone techniques is similar to that with the 3D-FS-GRE technique. However. the signal level of fluid relative to articular cartilage is

needed

data

FOV

is

so a surto

re-

the

short

quired.

so use

of this

areas

stricted

to a specific

sequence

region

can

must

he

ac-

be re-

of interest.

1225

Gold Three-Dimensional

Cone

The 3D cone

used,

technique

also has advantages

over existing techniques. Because the central K-space trajectory is similar to that of projecimaging

tion-reconstruction contrast

and lesion

3D cone technique than conventional technique about over

used

by Disler

The

scan about cm)

The

the same with

(1.0-mm3 voxel mm. Decreased

using

3D cone volume

1.0-mm

conven-

technique (12.8

can

x 12.8

isotropic

x

resolution

volume) in approximately scan times are possible

both the 3D fat-suppressed recalled echo and 3D cone

mm

spoiled techniques

5 for

gradientwith the

use of high-speed gradient systems. For exampie, using high-speed gradients and the 3D cone FOV

technique, one can image a 12.8-cm with 1.0-mm isotropic resolution in 2.8

mm. pulse

Use of the spectral-spatial in 3D cone may provide

pression

at TFs

tional techniques The 3D cone processing

time

similar

excitation better fat sup-

to those

of conven-

(TE = 6.6 msec) [9]. technique requires of 6 mm

a data

entire volume. The FOV is not limited by an antialiasing filter, so a surface coil or extremity coil

is needed

to prevent

aliasing.

Acqui-

sition of an anisotropic FOV may be possible with a modified 3D cone trajectory. Alternatively, if the spectral-spatial excitation is

1226

which

can

be rein the

images, can be corrected by the apof field-mapping techniques for off-

resonance correction subject of future study.

is also

seen

3D cone plication

be

the

In conclusion, in vivo high-resolution trashort TE imaging of articular cartilage

ulin

has 3D

been

images

isotropic

resolution.

be used

The water

peak

by line

We

plan

content

within

to study

with

can cartitimes

to distinguish and hyaline

between cartilage

ability

have

would

for the long-term

399-407

im-

success

of the transplant.

J, Macovski

spectroscopic

A, Herfkens

R. MR

of collagen: tendons and

imaging

knee menisci. Magn Reson Med 1995;34:647-654 6. Jackson JI, Meyer CH, Nishimura DG, Macovski A. Selection of a convolution function for Fourier inversion using gridding. IEEE Trans Med Imaging 1991;MI-10:165-174

P. Nishimura

7. Irarrazabal sional

autologous technique

with

site. This

implications

or failure

plane

technique

this

transplants

at the repair

in any

PRSI

echo time projection reconstruction MR imaging of cartilage with histopathologic correlation: comparison with fat-suppressed spoiled grass and magnetization contrast MR imaging. Radiology 1997;203:501-507 4. Gold G, Pauly J, Moreno J, Glover G, MacovskiA, Herfkens R. Characterization of atherosclerotic plaque at 1ST. J Magn Reson Imaging 1993;3: 5. Gold G, Pauly

on a conventional

area and relaxation

and hope to be able growth of fibrocartilage portant

will

with scan times of 5-10 technique provides mor-

lage by relative chondrocyte

and

ofcartilage

to assess width.

[12]

shown

scanner cone

phologic

magnetic

DG.

resonance

Fast three

imaging.

dimen-

Magn

Reson

1995;33:656-662

Med

8. Meyer

CH, Pauly

JM, Macovski

A, Nishimura

D.

Simultaneous spatial and spectral selective cxcitation. Magn Reson Med 1990;15:287-304 9. Block WH, Pauly JM, KerrA, Nishimura D. Consistent fat suppression with compensated spectral-spatial pulses. Magn Reson Med 1997;38: 198-206

10. Disler D, McCauley

T, Kelman C, et al. Fat-supthree-dimensional spoiled gradient-echo

pressed MR

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the The

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