John

Huston

III, MD

#{149} Daniel

A. Rufenacht,

MD

#{149} Richard

L. Ehman,

MD

#{149} David

0. Wiebers,

MD

Intracranial Aneurysms and Vascular Malformations: Comparison of Time-of-Flight and Phase-Contrast MR Angiography’ Twenty-seven patients with 14 aneurysms and 17 vascular malformations were each examined with both timeof-flight (TF) and phase-contrast (PC) magnetic resonance angiography of the head. Three-dimensional (3D) PC imaging depicted the patent lumen of the aneurysms, while 3D TF imaging depicted the patent lumen and a subacute thrombus if present. The 3D PC techniques were superior to 3D TF methods in depicting aneurysms larger than 15 mm. PC angiography allowed velocity resolution of vascular lesions and yielded functional flow information by directly depicting collateral flow to vascular lesions. Artifacts present on TF images were due to substances with short Ti, hemosiderin, and surgical clips. Artifacts present on PC images were due to flow-related aliasing. The results showed that PC techniques have specific advantages over TF techniques, including identification of large aneurysms, velocity resolution of vascular lesions, depiction of flow direclion about the circle of Willis, and less degradation by artifacts. Index terms: teriovenous

Cerebral Magnetic studies ogy,17.1214

Radiology

Aneurysm,

cerebral,

malformations,

blood

vessels,

resonance #{149} Magnetic

1991;

10.73

cerebral,

MR studies,

(MR), comparative resonance (MR.),

Ar-

#{149}

10.75

17.1214

T was

181:721-730

known

long

of magnetic nesoto flow phenomena before

the

cessfully

applied

to intracranial

dis-

ease (8-il). A significant drawback to PC imaging has been the long imaging time, which ranges up to 37 mmutes pen acquisition (10). New PC pulse sequences have substantially shortened the examination time (12). studies

systematically

comparing

PC and TF techniques as regards their ability to contribute to the clinical evaluation of vascular lesions have been reported, to our knowledge. The

purpose

of this study

was to compare

and contrast three-dimensional (3D) PC and 3D TF MR angiographic techniques in patients with intracranial aneurysms

From the Departments of Diagnostic ogy Q.H., D.A.R., R.L.E.) and Neurology I

Radiob-

(DOW.), Mayo Clinic and Mayo Foundation, 200 First St SW, Rochester, MN 55905. From the 1990 RSNA scientific assembly. Received February 21, 1991; revision requested April 3; final revision received July 8; accepted July 15. Address reprint requests to J.H. C RSNA, 1991

and

vascular

tages in the lesions.

evaluation

of vascular

technique

was applied to imaging. With the onset of MR imaging, flowing blood was noted to have distinct appearances (1). Initial efforts were directed to eliminating the complex flow effects from blood by using presatunation and gradient-moment-nubling techniques (2,3). Subsequently, pulse sequences and image-processing techniques were developed to provide projection angiographic images of flowing blood. The two major techniques for this purpose are time-offlight (TF) (4,5) and phase-contrast (PC) (6,7) angiography. TF imaging exploits the inflow of fully magnetized blood into a saturated stationary tissue. PC techniques make use of bipolar pulse sequences to detect a shift in the phase caused by blood flowing through a magnetic field gradient. Recently, both TF and PC MR angiographic techniques have been suc-

No technob-

sensitivity nance (MR)

HE

malforma-

tions. For that reason, the patients were studied with both techniques and the results were compared with those of conventional angiography, MR imaging, and computed tomography (CT). One of the hypotheses of the study was that the versatile velocity-sensitive capability of PC angiognaphy would provide specific advan-

MATERIALS

AND

Twenty-seven

METHODS

consecutive

patients

with

14 aneurysms and I 7 vascular malformations were examined with a I .5-T super-

conducting imaging system (Signa; GE Medical Systems, Milwaukee). Twenty-six of the patients underwent conventional arteriography, 27 underwent

16 underwent CT, standard spin-echo

and all MR im-

aging at the time of their MR angiography examinations. Standard MR head imaging was performed with sagittal Ti-weighted (repetition time msec/echo time msec 192

=

500-600/13-20;

views)

and

transaxial

(2,300-2,500/30, sequences.

80;

two excitations; T2-weighted

one excitation;

192

views)

Vascular

MR

imaging

was

performed

with the Multisequence Vascular Package (GE Medical Systems) with use of 3D IF, two-dimensional (2D) PC, and 3D PC techniques. The 2D and 3D PC sequences used

in this study

encode

have

for maximum

the capability

velocities

to

ranging

from 5 to 400 cm/sec. The echo time in all studies was automatically set to a minimum by the vascular imaging software.

The frequency-encoding anteroposterior

direction

in all cases.

Flow

was compen-

sation in the read and section direction was used with the TF and PC 3D sequences. In the PC studies, bipolar flow-encoding gradients were used. A 28section 3D IF sequence required approximately 3 minutes and a 60-section sequence, approximately 7 minutes. The 3D PC technique required approximately 7 minutes for a 28-section and 14 minutes for a 60-section volume acquisition. Approximately 20 minutes was required for the reconstruction and projection image postprocessing of a 60-section 3D PC study. During reconstruction and postprocessing, additional imaging was per-

formed.

Abbreviations:

AVM

=

arteriovenous

malfor-

mation, MIP = maximum intensity projection, PC = phase contrast, IF = time of flight, 3D three-dimensional, 2D = two-dimensional.

=

721

Figure 1. PC collapse

Sagittal image

2D PC scout with posterior

image (a), 3D subvolume

outlined (b), 3D collapse image with right carotid subvobume outlined (c), and 3D PC posterior subvolume (d) of a 70-year-old man with a 4-mm basilar tip aneurysm (arrowhead in d), obtained with use of 60 sections 1 mm thick. Images include the posterior infenor cerebeblar arteries. Note segment of right internal carotid artery partially included in the posterior subvolume (arrow in d) and black-and-white-reversed photographic technique.

Aneurysms A sagittal 2D PC scout image with 30cm/sec maximum velocity encoding was obtained to localize the volume for 3D TF and 3D PC imaging. Then 3D TF imaging was performed (40/4.3-4.9; one excitation; 192 views; flip angle, 20#{176}; field of view, 18 cm) with use of 28 or 60 axial sections be-

tween

0.7 and

1.0 mm thick.

3D PC angiography 36/7.4-8.2;

angle,

one

128

(26-

views;

flip

18 cm; maxi-

velocity encoding, 30-60 cm/sec) use of 28 or 60 axial sections between and

1.0

mm

nique proved medium and useful

as an

tab scout With quences, sity

excitation;

b.

Additionally,

performed

15#{176}-20#{176}; field of view,

mum with 0.7

was

a.

thick.

The

2D

PC

tech-

inadequate to evaluating small aneurysms but was approximate

2’/2-minute

for

sagit-

sequence. both the 3D IF and 3D PC sepostprocessing maximum inten-

projection

(MIP)

images

through

the

entire imaging volume were automatically generated. This resulted in 19 MIP images perpendicular (projection

eliminate sels,

to the axial imaging images) at 10#{176} increments.

the problem

postprocessing

tamed.

These

plane To

of overlapping subvolumes

subvolumes

were

yes-

were

ob-

selected

from the MIP image along the axial imaging plane (collapse image) of both the 3D IF and the 3D PC series. The collapse im-

age is a composite

of all the flow informa-

tion contained in the individual contiguous axial sections. A circle was used for the posterior circulation and a rectangle for

the right

and left carotid

distributions,

with care taken to include the anterior communicating artery in both carotid volumes (Fig 1). Viewing the individual subvolumes in a cine loop on an independent monitor enhanced the perception of the 3D relationship of the vessels and facii-

tated identification of small aneurysms. Surgical aneurysm clipping confirmed the

presence

of seven

aneurysms

in seven

of the 12 patients.

Vascular

Malformations

quently, 3D PC angiography was performed (25-33/4.7-9.7; one excitation; 128 views; flip angle, 15#{176}-20#{176}; field of view, 20 cm; maximum velocity encoding, 10-120 cm/sec) with use of 60 axial sections between 0.7 and 2.0 mm thick. Imaging of six of 17 patients with vascular lesions included use of the contrast agent gadopen-

tetate

722

#{149} Radiology

dimeglumine

(Magnevist;

Berbex

Imaging, Wayne, PC examinations

NJ). The 3D TF and 3D made use of the same

section

for

thickness

each

patient.

The

sec-

tion thickness was selected to encompass the entire vascular malformation and anticipated venous drainage as depicted on the 2D PC scout image, the standard MR head image, and the conventional angiogram. Nineteen MIP images in 10#{176} increments through the entire imaging volume were automatically generated with the 3D pulse sequences. Frequently, no additional postprocessing

A sagittab 2D PC scout image at 30-cm/ sec maximum velocity encoding was obtamed to localize the volume for 3D TF and 3D PC imaging. Then 3D TF angiography was performed (40/4.3-4.9; one excitation; 192 views; flip angle, O; field of view, 20 cm) with use of 60 axial sections between 0.7 and 2.0 mm thick. Subse-

d.

C.

subvolumes

were

obtained.

Some small vascular lesions required additional postprocessing subvolumes for complete evaluation. The conventional angiographic, CT, and MR images were reviewed together by two neuroradiobogists Q.H., D.A.R.). Therefore, the reviewers had knowledge of the

conventional

angiographic

findings

when

analyzing

the

MR angiographic

studies.

RESULTS

Aneurysms MR angiographic techniques permitted detection of all 14 aneurysms in the 12 patients previously identifled as having aneurysms by means of conventional angiography (Table 1). Aneurysms

were both size

even,

between

increased

the

nique. lumen artery carotid

beyond

15 mm

15 mm,

3D PC technique

gressively

seen

3 and

equally well demonstrated with techniques (Fig 2). As aneurysm

superior

how-

was

to the

pro-

3D TF tech-

IF imaging did not depict the of a 30-mm posterior cerebral aneurysm (Fig 3), and a 20-mm siphon lesion was very faintly on

the

collapse

image

but

not

detected on the projection images. The size of aneunyms as determined with MR angiognaphy was comparable

during

with

conventional

the

size

measured

angiography December

1991

Table

1

Results

of Evaluation

of Aneurysms MR

Conventional

Angiography

TF Technique

Size (mm )

PC Technique

S ize (mm)

Size

Signal Patient/Age

(y)/Sex

Location

of Aneurysm

1/43/M 2/70/M 3/70/M 4/49/M 5/38/M 6/65/F

Left anterior cerebral Anterior communicating* Basilar tip Right middle cerebral Anterior communicating Right superior cerebellart

7/27/M 8/52/F

Left middle cerebral Right cavernous ICA

9/63/F 10/61/F

SI

Right ICA siphon Left ophthalmic Right

ophthalmic

Right cavernous

:

11/30/F 12/64/M

Left posterior Fusiformbasilar*

Note.-AP = anteroposterior, * Subacute thrombus present. t Acute and subacute thrombi

ICA

=

ICA cerebral

internal

carotid

Angiography

#{192}Y RL

SI

AP

RL

(mm

Intensity

Signablntensity

of Fbowjet

SI

AP

RL

of FlowJet

3 3

3 3

3 3

3 5

3 5

3 5

ND ND

3 3

3 3

3 3

ND ND

4

4

4

4

4

4

High

4

4

4

High

5 8 6

5 6 5

5 6 9

9 11

10 8

. . .t

5 10 13 8

5 6 8 10

5 6 10 9

ND ND High High

5 10 4 8

5 6 3 10

5 6 5 9

ND Low Low High

8

11

10

10

High

11

10

10

High

7 4

11 4

10 4

7 4

10 4

9 4

High ND

7

9

9

High ND

. .

ND

.

5

5

5

4

4

4

19

19

28

...

20

25

High

20

25

27 44

29 11

33 12

45

ND 31

28

High ND

24 32

25 9

artery,

ND

=

not demonstrated,

RL

=

right to left, SI

ND

. . .

=

#{149}

.

#{149

High

. .*

30 7

High ND

superoinferior.

present.

Measurement not available. S The 2D PC technique in this case alone proved to be inadequate Aneurysm faintly visible on collapse image only.

in the evaluation

of small -

---- -----

aneurysms.

----.

I Figure

2.

a 3-mm

.-----.------------------------

Images

of a 43-year-old

left anterior

rysm. oblique

(a) Conventional view with

right)

shows

weighted

(arrow).

shows

containing

man

artery

angiogram head turned

the

aneurysm

image

rhage

cerebral

(lateral to the

(b) Ti-

subarachnoid

hemor-

methemoglobin,

is no evidence

with

aneu-

but there

of an aneurysm.

TR

=

repeti-

tion time, TE = echo time. The 3D TF (c) and 3D PC (d) projection images (both obtained with use of 28 sections 0.7 mm thick) demonstrate

the

aneurysm

(arrow)

equally

eral oblique views with the head the left). An air-bone susceptibility is evident

on

the

well

(bat-

turned to gradient

3D TF angiogram

(arrow-

head in c). Some of the signal intensity adjacent to the aneurysm on the 3D IF anglogram is due to the subarachnoid hemorrhage containing

methemogbobin.

b.

a.

short

Ti

(Fig

4). A maximum

velocity

encoding of 30 cm/sec with the 3D PC sequence best demonstrated slow flow within aneurysms. The intrinsic flow pattern within the aneurysm was frequently seen in aneurysms larger than 5 mm (Table 2). The orientation of the entry flow jet in relation to the parent artery as well as the neck and dome of the aneurysm was often cleanly seen (Fig 3). Patient 6 had a significantly smaller

r d.

C.

--- .--“-



lumen at 3D PC imaging ventional angiography. studies thrombus

(Table patent tional Volume

1). PC techniques lumen as depicted angiograms, while 181

#{149} Number

3

reflected the on convenIF tech-

niques as well taming

represented as a subacute methemoglobin

the patent lumen thrombus conthat had a

showed that

evidence decreased

than at conCT and MR of an the

acute

lumen

during the 10 days between penformance of conventional angiography and performance of MR angiography. Radiology

#{149} 723

Vascular

Malformations

MR angiognaphic techniques albowed detection of 11 arteniovenous malformations (AVM5), one brain anteniovenous fistula, one dural arteriovenous fistula, and a venous angioma previously

identified

with

conven-

tional angiography (Table 3). Also identified was a lesion consistent with a cryptic vascular malformation in a patient who did not undergo conventional angiography (13-15). With use of the angiographic and standard MR images, the nidus was comparable

size of the AVMs with that at conven-

tional angiognaphy. A 5 x 8 x 12-mm slow-flow AVM and a small thalamic cavernous hemangioma were not visualized at MR angiognaphy. However, both lesions were easily seen on gadolinium-enhanced thin-section Ti-weighted images. Two patients had aneurysms on the feeding artenies to their

AVMs.

The 3D IF technique permitted visualization of the feeding arteries and the size of the nidus of mediumand high-flow AVMs. The proximity of the AVM nidus to the internal carotid and basilar arteries was related to the intensity

of the

nidus, Those

eral

signal

within

to saturation

lesions

that

had

cause

flow

owing lower

the

were

signal

feeding

the

effects. more

periph-

intensity

vessels

be-

traveled

through more of the saturated imaging volume. The 3D PC technique depicted the feeding arteries, nidus, and draining veins of mediumand high-flow AVMs,

depending

on

coding. A maximum ing of 10-20 cm/sec and medium-velocity tunes,

while

of greater

cm/sec

yielded

arteries, nidus, veins (Fig 5). The number was

identified quite

velocity

en-

encod-

highlighted

slow-

venous

a maximum

coding

branches raphy

the

velocity

of the

to 60 feeding

ity encoding was tiate the high-flow

high-velocity

of feeding with variable.

maximum

velocity

3D PC image of a left (patient 13). Frequently, obscured adjacent seen during the

MR angiogAll of the

encoding

PC images. of

conventional angiography. Angiographicalby proved direct anteriovenous fistulas were seen associated with AVMs in two patients or isolated in one patient. The 3D PC technique with high maximum veboc724

#{149} Radiology

fis-

Patient 7, who had a large single direct arteriovenous fistula, showed an associated aneurysm with distinct MR angiographic characteristics of an internab flow jet on both 3D IF and 3D

pnecentral AVM the nidus

arteries clearly early arterial phase

useful to differenanteniovenous

tula from the associated AVM. MR angiographic findings for arteniovenous fistulas included a small nidus compared with the relatively large size of the arterial feeding arteries and barge ectatic veins with high flow.

arterial

feeding arterial branches identified with conventional angiography were identified at MR angiography in only one patient. This occurred on a 60cm/sec

Figure 3. Images of a 30-year-old woman with a giant fusiform aneurysm (30 mm) of the proximal left posterior cerebral artery. (a) Flow jet (arrow) is demonstrated on an early arterial image obtained with digital subtraction angiography. (b) Sagittal 2D PC image obtained in the midline with 30-cm/sec maximum velocity encoding demonstrates the giant aneurysm (arrow). (c) A 3D PC projection image obtained with use of 60 sections 0.7 mm thick demonstrates the flow jet (arrow) and aneurysmal lumen (arrowheads). (d) A 3D TF projection image obtained with use of 60 sections 0.7 mm thick demonstrates the flow jet (arrow) but does not depict the lumen. The 3D TF collapse image also failed to depict the lumen. Note the wider arterial lumina on the 3D PC image compared with those on the 3D IF image.

en-

or equal

images

and

struc-

velocity

than

d.

C.

In retrospect,

this

mum

3D PC technique velocity

sec allowed

encoding

identification

with

vascular

malformations.

Six of the

seven patients with deep venous drainage were identified with use of a maximum velocity encoding of 20 cm/sec

or slower.

Gadolinium enhancement improved the visualization of the vasculan structures with both 3D IF and 3D PC techniques. The increased visibility was more tunes (Fig 7).

evident

in venous

struc-

aneu-

rysm was visible on the conventional angiogram but not clearly distinguishable from adjacent, rapidly filling yenous structures (Fig 6).

The

draining veins observed with conventional angiognaphy in four of the 14

a maxi-

of 10-20

cm/

of all the

DISCUSSION Previous reports have efficacy of MR angiography

explored th in depict-

ing intracranial

structures.

These

studies

vascular have

used

either

December

IF

1991

Table 2

Depiction Flow

of Aneurysmal

Internal

Jets

No. of Flow Jets Seen with Technique Aneurysm Size (mm)

Total No. of Aneurysms

3D TF

3D PC

5 >5

6 8

1 6

1 7

techniques were performed with somewhat different matrix sizes and total acquisition times. The 3D IF studies

were

spatial

b.

a.

performed

resolution

with

than

higher

the 3D PC

studies and required less acquisition time when performed with use of parameters similar to those reported in

published trix sizes studies,

studies (8,9). If similar mawere used in the 3D PC the

acquisition

time

would

be

unacceptably long. In planning this study, it was hypothesized that the use of fewer phase-encoding steps for 3D PC studies may

be acceptable

given

unique

physical

of these

tions. sitions

basis

Nevertheless, the were approximately

the

3D

acquisi-

PC acquitwice as

long. It is conceivable that some of the results of the 3D IF studies could have been improved by allowing an acquisition time similar to that of the PC studies. For instance, it may have been possible to improve the depiction of slow-flowing blood by reducing saturation effects (16). However, some

of the

areas

in which

demonstrated special the 3D PC technique on

d.

C.

Figure 4. Images of a 64-year-old man aneurysm. (a) Conventional angiogram posterior view). The proximal aneurysmab

weighted

MR image

extrinsic maximum angiogram.

lumen

shows

a large

with a partially thrombosed obtained by means of left lumen is outlined with

amount

to the patent lumen (arrow). TR velocity encoded 3D PC projection Slow flow through the fusiform

size (arrows)

image does not ing methemoglobin.

to saturation

allow

effects.

unsaturated

blood

when

compared

with

of subacute repetition

=

image, aneurysm

that

thrombus time, TE

The left posterior the

anterior

cerebral

=

on the conventional

artery

fusiform basilar vertebral injection arrows. (b) Sagittal

containing echo time.

from the of the

(arrow)

artery (anteroTi-

methemoglobin (c) A 45-cm/sec

which is analogous to the results in an underestimation

differentiation of the patent lumen Slow flow resulted in nonvisualization from

the

angiogram.

(d) The 3D IF

is visualized

due

containowing

to inflow

of

circulation.

or PC

(9,10)

techniques.

The

goal of this study was to directly compare and contrast 3D IF and 3D PC angiographic sequences in a series of patients with intracranial aneurysms and vascular malformations. The main differences in the results obVolume

181

#{149} Number

3

physical

basis

resistance

with IF in depiction

ena, depiction short Ii, and

and

PC techniques of flow phenom-

of substances having the specific artifacts that

affect each technique. In reviewing these be noted that the 3D

it should 3D PC

arti-

Phenomena

While all aneurysms were identifled as morphologic abnormalitiesanalogous to the results achieved with conventional angiographyinternal

flow

jets

3). Creation

dependently

and

disruption

of

were addibe observed

of subvolumes

view

to in-

carotid

arteries

and evaluation of aneurysms. flow jets were demonstrated

aging

aneurysms

in seven (Table

crucial

and

cation Internal and

was

the

basilar

in eight results, IF and

of the

to certain

flow in the parent artery tional findings that could tamed were

results

These capabilities include background suppression, of functional flow informa-

and

Flow

conventional of the

subacute thrombus distal basilar artery

tion, facts.

(Fig (8,11)

unique

method. superior provision

the

capabilities for seem dependent

with

aneurysms

for

identifi-

PC

imaging

with

IF

2). In all saccular

Radiology

im-

aneu-

#{149} 725

--

banger than ing demonstrated All flow jets were of increased signal IF technique. Six observed with PC rysms

as increased

bow-intensity to phase complex the internal aneurysms, ous studies niques

5 mm, 3D PC imagan internal flow jet. depicted as streams intensity with the of the eight flow jets imaging were seen signal intensity. The two flow jets were attributed dispersion associated with flow. Ihe flow jet indicated flow pattern within the as demonstrated by previin which cine MR tech-

were

used

(17-19).

The

artifact

of MIP

display

the

amount

,-

-

‘-4

-

m m o

-

-

0

-

0

0

0

-

‘-

0

C

0

Lfl

0

C’)

‘-4

c

-



0

e

0

0

ri

r’i

N

r’

-

0

0

0

‘-



0

0

I.. t’

-

slow

(21).

venous

flow

.2

U

51

.0 (U

>

(U

0 C (U

‘5 U

.

0

5)

=

0

0

0

0

0

0

r

0

0

0

‘-

0

#{149} Radiology

0

(U

0

5)

0

0

0

0

0

0

0

0

0

0

0

0

0

(U 5) 0 0

0



0 51 ‘0

4

tn

4

c

‘-

c’

c’

e-

e

0

0

0

0

u’#{176}

z

0

ici

5)

.L

I

5)

.

z

g

.

5)

i

z

25) 0 a.

5) 0

z

0

0

z

z

OOOOOOOOOO

‘)

‘)

)-

>

a)

ZZZZZZZZZ)-

0

5)

5) >.

-C 0 c

4)

.u

:

r-

.

o

-

.-

0

0

C’

0

0

0

u

U)

C 0

* ,-

‘-

c-

-

:-

e-

m e-

0

.-

0

0

z

-

(1)

,

.

\o

‘,o

so

C)



.O ‘0

F-.. ‘5. so -



. 0

0

.E

.

z -3

(5

.

5)

5)

of velocity

venous

flow

is

i,

is demonstrated

.C C

(U

a

0

Intracranial aneurysms and vascular malformations: comparison of time-of-flight and phase-contrast MR angiography.

Twenty-seven patients with 14 aneurysms and 17 vascular malformations were each examined with both time-of-flight (TF) and phase-contrast (PC) magneti...
2MB Sizes 0 Downloads 0 Views