Robert Thomas

C. Smith, MD R. McCauley,

Fast ofthe

In this

Spin-Echo Female I#{149} Use

Part

Caroline Reinhold, MD #{149}Ruben Kier,

#{149}

ofa

prospective

Whole-Volume

study,

magnetic

Robert C. Lange, Shirley McCarthy,

terms:

sequences

resonance

Magnetic Pelvic

#{149}

S

resonance (MR), organs, MR. 85.1214

pulse

1992;

184:665-669

sary for structure

T2-weighted

pulse

visualization and detection

of gynecobogic of most pelvic

abnormalities. The acquisition time for T2-weighted images with conventional sequences is approximately 9 minutes. These images frequently contain phase ghost artifacts and blurring caused by both voluntary and involuntary physiologic motion (including respiratory motion, bowel peristalsis,

and

These artifacts not eliminated, tory

motion

vascular

pulsation).

can be reduced, but by means of respiracompensation

tech-

niques, administration of glucagon, and presaturation of inflowing blood. The long examination times and cost currently prevent MR imaging from becoming the initial imaging modality for most pelvic abnormalities. Conventional spin-echo (CSE) pulse sequences acquire echoes at fixed times after each section-selective 90#{176} excitation pulse. When MR imaging is performed with long repetition times (TRs), multiple echoes two)

are

usually

These echoes have the encoding (ie, the phase changed

between

acquired.

same phase encoding is measurements

of the separate echoes). This allows reconstruction of multiple images per section location, each with a different echo time (TE). For a two-echo, long-TR sequence, this yields intermediate and T2-weighted images at each location. The phase-encoding gradient of a CSE

I From the Department of Diagnostic ing, Yale University School of Medicine, dar St, New Haven, CT 06510. Received ber 18, 1991; revision requested January revision received January 30; accepted 24. Address reprint requests to R.C.S. C RSNA, 1992

(SE)

PIN-ECHO

sequences are essential for magnetic resonance (MR) imaging of the body, particularly for MR imaging of the female pelvis. T2 contrast is neces-

not Radiology

MD

Coil’

(typically Index

PhD PhD,

#{149} #{149}

MR Imaging Pelvis

axial and (MR) images were obtained with T2weighted conventional spin-echo (CSE) and fast spin-echo (FSE) sequences in 34 consecutive female patients who underwent clinical pelvic MR examination at 1.5 T. The MR images from each patient were compared side by side, blindly and independently, by two radiologists experienced in MR imaging who used a standardized score sheet for anatomic and pathologic findings. The FSE sequences were rated superior significantly more often than the CSE sequences in most categories of findings (P < .05), including overall image quality and reduction of motion artifact. The examination time for the FSE sequences was 1 minute 46 seconds versus an examination time of 9 minutes 14 seconds for the CSE sequences. (Both CSE and FSE Sequences provided 18 sections.) It is concluded that the FSE sequence provides T2-weighted anatomic and pathologic information superior to that provided by the CSE sequence and requires substantially less imaging time. sagittal

MD MD

Imag333 CeNovem7, 1992; February

sequence

induces

phase

changes

necessary for positional information along the phase axis. On the other hand, gradient-induced phase changes cause signal loss. The amount of signal loss is proportional to the strength of the gradient. Therefore, echoes acquired with bow-magnitude phase gradients provide most

of the

signal

images

and

contrast

of CSE

MR

(1-3).

To increase imaging speed, a different phase-encoding gradient can be used for each echo of a multiecho train after a 90#{176} radio-frequency pulse. This increases the amount of data acquired per section per TR interval. Such a sequence was initially described by Hennig et ab (4,5) and was

referred

to as rapid

acquisition

with relaxation enhancement Recently, a variant of this has

been

described

and

(RARE). sequence used

for

clini-

cab MR imaging by Melki et al (6). Their variant of the RARE sequence is referred to as fast-acquisition interleaved SE. More recently, this has been shortened to fast SE (FSE). The FSE sequence acquires a train of up to 16 SEs after each section-selective 90#{176} pulse. This is achieved by applying multiple 180#{176} pulses in rapid succession to generate multiple echoes. A different phase-encoding gradient is used for each echo. (The phase-encoding gradients are applied after each 180#{176} pulse and then rewound prior to the next 180#{176} pulse.) The number of 180#{176} pulses applied is referred to as the echo train length (ETL),

and

the

oes is referred (E-space).

spacing

between

to as the

When

the

echo

phase

ech-

spacing gradients

are ordered so that, for each section, the low-magnitude gradients are used for the nth echo (n 16) of each echo train, an MR image with an effective TE (or pseudo-TE) of n times E-space is produced

(6).

TR, number

of phase

(NPE),

and

number

Therefore,

for

equal

encodings of signals

aver-

aged (NSA), the FSE sequence can reduce imaging time by a factor equal to ETL. The imaging time for the FSE

Abbreviations: CSE = conventional spin echo, E-space = echo spacing, ETL = echo train length, FOV = field of view, FSE = fast spin echo, RARE = rapid acquisition with relaxation enhancement, SE = spin echo, TE = echo time, TR = repetition time.

665

Comparison

of Image

Scorer

Scores

Based

FSE

CSE

I 2

27 29

5 3

1 2

23 26

5 0

on FSE

CSE Sequences

and

E

Overall

P Value

FSE

CSE

NA NA

.001

.001

27 29

3 1

Cervical

.001 .001

18 10

6 5

Margins 2 7 Anatomy

Reduction

4 4

NA NA

Zonal

Anatomy

.001 .001

(CE)

8 17

.01 NS

2 2

CervicalZonal

(IZ)

P Value

N

Artifact

Cervical 4 1

Zonal

E

Motion

Quality 2 2

Cervical

N

Anatomy

(ST)

1 2

2

0

0

32

NS

19

8

6

1

.03

6

0

4

24

.02

12

3

17

2

.02

1 2

16

4

5

9

17

2

10

5

.006 .001

24 27

2 2

1 1

.001 .001

1

19

5

5

5

2

23

2

6

3

.004 .001

18 21

6 4

Cervical

Zonal

Uterine

Zonal

Anatomy

Left Ovary 1

16 11

2

Anatomy

2 4

13 12

1

2 1

6 10

4 1

2

1 2

0 2

1 0

.025 .002

5 9

1 0

NS NS

Ovarian

Right NS NS

1

4

7

1 0

1 2

6

1

5

1

I 2

3

29

NS

2

29

NS

Ovarian

Mass

31

NS

2

31

NS

1

26

.06

4

24

NS

3 0

0 0

Venous

Vaginal

Cysts 0

34

2

32

7 11

NS NS

22 22

.06 NS

22 32

NS NS

Margins 9 2

Ovarian

0

Plexus

5 10

Cysts

0

Lesions

2

6 1

0

.07 NS

0

1 1

0

15 16

0

NS .01

Bartholin

.03 NS

1

28 26

Nabothian

10 9

Implants

Endometrial

Perivaginal

1 1

.01 .001

1

Adenomyosis

2

4 2

Stroma

2 1

1 3

Mass Lesions 32 32

Ovarian

5 6 Right

29 31

OlE)

Identification

5 7

12 11

Implants

1 0

Ovary

Right 10 12

2 1

Left Ovarian

14 9

Anatomy

6 7

Stroma

Endometrial

1 1

Zonal

Right

.001 .06

Margins 7 4

Uterine

(M/J)

10 9

7 9

Left Ovarian

Uterine

Identification

Left Ovarian 1 2

(OZ)

Leiomyomas

3

5

19

NS

1

7

15

.003

Note-Numbers in the FSE and CSE columns indicate the number of cases in which each of the sequences was rated superior. cE = inner bright zone, E = number of cases for which the FSE and CSE sequences were rated equal, IZ = adjacent zone of intermediate signal intensity, J/E = junctional zone/endometrium, M/J = myometrium/junctional zone, N = number of cases in which a finding was not identified with either sequence, NA = not applicable, NS = not significant, OZ = outer zone continuous with the myometrium, ST = dark zone of cervical stroma.

sequence

is given

by the following (TR x NSA X NPE)/

equation: Tscan ETL. Depending and the E-space, tions

may

on the choice of ETL the number of sec-

be reduced

compared

with

a CSE sequence of equal TR. When an FSE sequence is used, weighted images can be acquired less ing

than times

motion

artifact.

report

of the

sibibity

666

These reduce

The

is to provide

tion male

1 minute. should

clinical

of the

pelvis. Radiology

#{149}

FSE

T2in

short imagphysiologic

purpose

of this

an

evalua-

initial

usefulness sequence

MR images

and in the

obtained

CSE

sequences

were

directly

com-

Committee

group

cab pelvic MR examinations. A direct comparison of image quality and detection of normal anatomic structures was made. It was not the purpose of this study to compare lesion detection

ages

ranged

age,

35 years).

tamed

from

in specific

diseases.

consisted

patients

the

fe-

with

MATERIALS Approval from

the

for this University

to us

during from

interview

study Human

study

for

MR

all before

during

examination

Their

(mean

consent

patients

of

period.

17 to 70 years

Informed

female imaging

was our

obroutine

with

MR

imaging. All MR

imaging

was

(Signa;

body GE

Medical

performed

coil and

with

a 1.5-T

Systems,

Mibwau-

series of coronal was obtained,

obtained

sagittal

T2-weighted

Investigation

quences

and were

axial

CSE

performed

with

a

sys-

kee). After a bocalizer weighted MR images

METHODS was

Our

a 10-week

whole-volume

AND

institution.

of 34 consecutive

referred

pelvis

tern

fea-

at our

pared with MR images obtained with FSE sequences at identical locations in a series of patients undergoing clini-

Tise-

the

September

follow-

1992

ian cysts, anatomy,

uterus margins, uterine leiomyoma of the uterus,

identification,

ovarian

stroma,

zonal ovary

individual

ovarian cysts, ovarian mass lesions, ovarian endometrial implants, adenomyosis, vaginal margins, perivaginal venous plexus, and Bartholin cysts. Each finding was

scored

for

superior,

conspicuity,

B superior,

fled. The

assessment

as follows:

equal,

or

of overall

not

A

identi-

image

quality

included quality of visualization of any abnormalities present. This enabled diagnosis whenever abnormalities were seen

on MR images quence

a.

b.

Figure

1.

the same structures

MR images

obtained with (a) CSE and patient. Note the improved visualization in b. A nabothian cyst is present within

(b) FSE sequences of the uterine the cervix.

at identical margins and

locations in uterine zone

but

with tected from

with

one se-

not on MR images

obtained

obtained

the other sequence. with both sequences this study. Evaluation

findings

was

the

and left anatomy

right zonab

me

performed

uations of the metrium/junctional

individually

for

sides. Evaluation included separate

interface

between and

zone

zone/endometnum. structures

Lesions not dewere excluded of all ovarian

the myojunctional

Evaluation

included

separate

of utereval-

of cervical evaluations

of four distinct zones: an inner bright zone, an adjacent zone of intermediate signal

intensity,

stroma,

a dark

and

an outer

zone

with the myometnum. ovarian endometriosis

accordance

with

Structures section

not locations

of cervical

zone

continuous

Adenomyosis were identified

previous present were

reports on the scored

and in

(7-12).

evaluated as not iden-

tified. Interobserver gory of finding

weighted each rately. as A

b.

Figure 2. (a) MR image obtained with CSE sequence shows poor definition margins because of motion artifact. (b) MR image obtained with FSE sequence cation fundal

in the same leiomyoma

patient (arrow).

as in a shows

clear

delineation

of the

uterine

and

of the uterine

margins

at identical as well

loas a

variability was analyzed

kappa

statistic

scorer were then In each category,

for

catea

(13). The

data

for

analyzed sepathe cases scored

B or not identified

=

the remaining

each with

were

cases

discarded,

were

statistical significance by tailed binomial distribution. were considered significant

tested

for

means of a oneThe results at P < .05.

RESULTS ing parameters: 2,000/20, 80;

section 2.5 128

thickness,

mm;

two

5 mm;

signals

intersection

averaged;

and

gap, a 256

matrix.

These parameters provided sections in 9 minutes 18 seconds. Respiratory compensation, no phase wrap, and superior and inferior saturation were used. Glucagon was not tered before MR imaging. After performed,

the

In each case, ing parameters

TR msec/TE msec = field of view (FOV), 28 cm;

CSE imaging sagittal and

x 18

were se-

quences were performed at the nine central section locations in each plane, which were selected on the basis of the CSE sequences. The nine central sections were chosen to include the uterus and ovaries. The FSE MR images were obtained with the following parameters: 2,900/126; ETL, 16; E-space, 18 msec; FOV, 28 cm; section thickness, 5 mm; intersection gap, 2.5 mm; two signals averaged; a 256 x 128 matrix; and no phase wrap. Superior and inferior saturation parameters tions

pulses were also used. provided nine section

184

Number

#{149}

locations identical

3

and

the

nine

for the CSE nine section

sequence rate films.

were

central

sequence locations

photographed

All photography

was

These boca-

images but were chosen trast and make the images

imagthe

onto sepaperformed did

not differThe standardCSE MR

to optimize as similar

conin

appearance as possible. Each case then consisted of two axial and two sagittab films of nine images per film. The FSE CSE or B case two ized

and

films were then randomly labeled A for each case. The four films for each were then compared side by side by radiologists experienced in MR imag-

ing (T.R.M., score

SM.), sheet

anatomic

and

quality,

motion cervical

who that

pathologic artifact zonal

used

listed

a standardthe

findings: reduction, anatomy,

All of the as

section and the for the FSE

radiologist (R.C.S., who interpret the images) to minimize ences in photographic technique. window and level settings were ized separately for the FSE and

margins,

in 53 seconds.

Volume

images,

and from

by one

pulses adminis-

sequences axial FSE

MR

all patient data were removed

following overall cervical naboth-

either

categories

were

rated

substantial agreement .80) or almost perfect (.81 K 1) except

(.61 K agreement for cervical zonal structures, ovarian stroma, and right ovary identification. The results of the comparisons of the MR images obtained with FSE sequences and those obtained with

CSE

sequences

are shown

separately

for each ble. This

of the two scorers in the table shows the number

cases

in

rior,

CSE

which was

CSE

were

was

not

Levels

rated visible

FSE was rated rated superior, equal, with

of significance

each category. The FSE sequences

supeFSE and

or the either

are

were

Taof

finding

sequence.

shown

for

superior

to the CSE sequences and enabled shorter examination times. The FSE sequences were rated superior significantly more often by both scorers for

Radiology

#{149} 667

the following categories of findings: overall image quality, reduction of motion artifact, and depiction of left ovarian stroma, uterine margins, uterme zonab anatomy, and cervical margins.

Typical

Figures findings differences

examples

1-4. no

anatomic the

in

of no

findings

CSE MR significantly

images more

FSE MR images

which

shown

categories

statistically significant existed. There were

or pathologic

which superior

the

are

In the other

nor

a pathologic

for

were often

any

rated than

cases

abnormality

in was

detected with one sequence but not with the other. Evaluation of vaginal margins and perivaginab venous plexus was limited by the fact that only the nine centrab section locations were compared. Thus, the axial MR images often did not cover this region of interest because

the

sections

dude

the

uterus

were

and

chosen

a. Figure Note

cystic

b. 3.

CSE (a) and

the

improved

right

FSE (b) MR images

obtained

visualization

of the

mass

to be a paratubal

adnexal

proved

ovarian

at identical

stroma

and

locations

uterine

in the same

margins.

patient.

At surgery,

the

cyst.

to in-

ovaries.

DISCUSSION This study provides an initial evabuation of the capacity of the FSE sequence to generate clinically useful T2-weighted

pelvis.

MR

Our

sequence T2-weighted

results provides MR

images

indicate

of the

that

female

this

superior quality images with signifi-

cantly shorter examination times than CSE sequences. This study did not formally compare the two techniques in detection or depiction of specific disease entities. The FSE sequence used in this study provides nine sections in 53 seconds with a TR of 2,900 msec. To provide more coverage of the pelvis and thereby include both the true and false pelvis, a concatenated acquisition 106 seconds long (providing 18 section locations) would be required. Alternatively,

nonconcatenated

acqui-

sitions with a TR of 5,800 msec and an ETL of 16 or with a TR of 2,900 msec and an ETL of 8 could be used. Both of these would provide 18 sections in 106 seconds. However, the time of data acquisition for each section bocation is doubled with the nonconcatenated sequences because the concatenated sequence acquires all of the data for half of the sections during the first 53 seconds and all of the data for the other half during the second 53 seconds. Thus, the nonconcatenated acquisitions would have more motion artifact. A longer TR (2,900 vs 2,000 msec) was used for the FSE sequence to provide adequate imaging coverage while a short imaging time was maintamed. Depending on the choice of 668

Radiology

#{149}

a. Figure cervical

b. 4.

MR images cancer.

The

(a) CSE MR image

obtained

in pregnant

examination

was

is severely

degraded

woman

performed

because

aged

for staging

23 years before

of fetal motion

with

a clinical

termination

artifact.

Fetal

diagnosis

of

of pregnancy.

and

placental

detail is absent. An area of increased signal intensity within the cervix (arrow) likely represents the tumor. (b) On the FSE MR image, obtained in 53 seconds, the discrete margins of the tumor and the surrounding fibrous stroma (curved arrow) can be confidently identified. Fetal and placental structures are delineated; the heart (small straight white arrow), liver (large straight white arrow), spine, cerebral ventricles, and umbilical cord (black arrows) are now discernible.

the

ETL,

the

number

can be obtained may be less than

with the

of sections an FSE number

with a CSE sequence with TR. We chose the maximum ETL to minimize longer TR only signal-to-noise

that sequence obtained

an identical possible

imaging time. The minimally increases ratio. Furthermore, in

the FSE sequence, we used an effective TE that exceeded the TE used in the

CSE

sequence.

The

effective

TE

was chosen to make the contrast characteristics of the gynecobogic structures as similar as possible between the two sequences. Identical values of these parameters do not yield images of identical contrast.

With

few

exceptions,

the

contrast

characteristics of the CSE and FSE MR images in this study are similar. The contrast characteristics of structures

affected by specific diseases on FSE MR images were not studied. The rebative signal from subcutaneous fat is greater on FSE MR images than on CSE MR images, a finding previously described not been knowledge,

(1,3,6). One finding previously described, and that was not

explored

in our

study

is that

that has to our formally

skeletal

muscle, leiomyomas, and intervertebral disks are more hypointense on the FSE than on the CSE MR images. This may be associated with the par-

September

1992

ticular choice of parameters used in our study. It has been noted that FSE sequences can cause image blurring when a bong EU and short effective TE are used (3,6). Even though a long ETL (16) was used, we did not observe any significant image blurring in comparison with the CSE MR images. This is consistent with the long effective TE chosen (126 msec). Although proton density-weighted MR images without blurring can be obtamed with the FSE sequence and a shorter ETL, we believe that proton density-weighted MR images rarely add any additional information. To ascertain whether a lesion contains lipid or blood, Ti-weighted MR images can be obtained with fat or water suppression (14). While proton den-

FSE sequences and have had no problems with power deposition. However, it is currently recommended that the FSE sequence not be used in patients over 250 lb (113.5 kg) or in patients whose body configuration is such that the area being imaged would touch the sides of the bore of the magnet. This precaution is prelimmary and may be changed in the future. Since completion of our study, we have noted improved quality of FSE images obtained with the body coil and a 256 x 192 matrix. This matrix increases imaging time by 50% compared with a 256 x 128 matrix. However, this amounts only to an increase from approximately 2 minutes per imaging

plane

to 3 minutes

per

184

#{149} Number

3

1.

Mulkern

RV, Melki

PS, Jakab

N, Higuchi

0,

Jolesz FA. Phase-encode order and its effect on contrast and artifact in single-shot rare sequences. Med Phys 1991; 18:10322.

3.

4.

5.

6.

1037. Twieg

DB.

lation

of the NMR imaging

The

k-space

trajectory

formu-

process

with

applications in analysis and synthesis of imaging methods. Med Phys 1983; 10:610621. Mulkern RV, Wong STS, Winalski C, Jolesz FA. Contrast manipulation and artifact assessment of 2D and 3D RARE sequences. Magn Reson Imaging 1990; 8:557-566. HennigJ, Nauerth A, Friedburg H. RARE imaging: a fast imaging method for clinical MR. Magn Reson Med 1986; 3:823-833. Hennigj, Friedburg H. Clinical applications and methodological developments of the RARE technique. Magn Reson Imaging 1988; 6:391-395. Melki PS, Mulkem RV, Panych LP, Jolesz

FA. Comparing the FALSE method with conventional dual-echo sequences. JMRI

imag-

ing plane. In addition, the minimum sity-weighted images might be helpecho spacing of the FSE sequence has ful in these circumstances, they been reduced to 13 msec. This prowould not be diagnostic. In patients vides additional sections per TR interwho undergo evaluation for bladder val. The FSE sequence can be used to carcinoma (a group of patients not included in this study), proton denacquire axial, sagittab, or coronal T2sity-weighted MR images can be very weighted MR images of the female helpful. pelvis with an examination time of 1 Because of the large number of 180#{176} minute 46 seconds, providing 18 section locations in each plane. A coronal pulses applied in rapid succession T2-weighted FSE sequence can be whenever the FSE sequence is used, power deposition becomes a concern. used as a localizing sequence. Sagittal In a previous study by Melki et ab (6), and axial T2-weighted FSE sequences a saline phantom was used to evalucan then be followed with a convenate power deposition associated with tional axial Ti-weighted sequence. FSE sequences. Temperature changes The total examination time for all four sequences is less than 10 minutes. If induced in the phantom were well one allows time for setup before exbelow the guidelines of the Food and Drug Administration, which recently amination and between sequences, an approved the FSE sequence used in entire pelvic MR study can be compbeted in less than 20 minutes. Therethis study for clinical imaging. Since completion of this study, we have exfore, FSE sequences enable marked amined more than 350 patients with reduction of imaging time compared with CSE sequences, while improving overall image quality. U

Volume

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Radiology

#{149} 669