6i 7

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Diagnosis Children:

Anne M. Hubbard1 James S. Meyer Soroosh Mahboubi

of Liver

Disease

in

Value of MR Angiography

We retrospectively studied the clinical use of MR angiography, a gradient-echo technique susceptible to motion, in the preoperative evaluation of the hepatic vasculature in children with liver disease. Twenty imaging examinations were performed in 18 patients 3 months to 10 years old (mean, 2.3 years). Eleven patients had liver tumors and seven had cirrhosis associated with biliary atresia, cystic fibrosis, and short-bowel syndrome. Respiratory motion artifacts were present in most patients, but all MR angiographic

studies

were

technically

adequate.

Comparing

MR

angiograms

with

spin-

images, we found that vascular visualization was better with MR angiography in 12 cases (60%), equal in five (25%), and worse in three (15%). In 10 of 20 cases, MR angiography provided additional vascular information not present on spin-echo images. MR angiography is a useful adjunct to spin-echo imaging for assessing hepatic vascular anatomy in children with liver disease. echo

AJR

[i

159:617-621,

1992

September

MR imaging is being used increasingly in the evaluation of liven disease in adults It has also been found useful in the evaluation of childhood liver diseases,

].

especially

tumors

[2, 3]. Gradient-echo

flowing angiography is potentially useful in the evaluation of hepatic vessels in liver tumors and in diffuse liven disease in children. In adults, good vascular definition has been obtained by using gradient-echo pulse sequences acquired in a single breath-hold [8]. Inasmuch as breath-holding by children is unreliable or impossible, this technique

blood (MR angiognaphy)

is

usually

not

angiognams this

technique

ventional

Materials

feasible.

obtained

This

study

in children

provides

spin-echo

pulse

are being applied

was

without

additional

done

to

used

the body

evaluate

breath-holding

vascular

(SE) sequences

sequences

throughout

information

to study

[4-7].

the

MR

quality

and to determine when

compared

of

MR

whether with

con-

of the liven.

and Methods

MR angiography was performed in 18 consecutive patients scheduled for MR imaging of liver disease. The patients ranged in age from 3 months to 10 years old (mean, 2.3 years). Eleven patients had liver tumors (three hemangioendotheliomas, five hepatoblastomas, one hepatocellular

carcinoma,

one

embryonal

Two patients with hepatoblastoma Received December 26, 1991 ; accepted after revision February 19, 1992. 1 All authors: Department of Radiology, The Chil-

dren’s

Hospital

Center Blvd., print requests

of Philadelphia, 34th Philadelphia, PA 19104. to A. M. Hubbard.

0361-803X/92/1593-0617 0 American Roentgen Ray Society

St. & Civic Address re-

cell

sarcoma,

were imaged

and

one

metastatic

neuroblastoma).

MR images were obtained before liver liver disease caused by extrahepatic biliary twice.

transplantation in seven patients with diffuse atresia(five), cystic fibrosis (one), and short-bowel syndrome (one). All imaging was performed on a Siemens 1 .5-T Magnetom unit. A knee coil was used for infants (two cases), a head coil for children weighing less than 20 kg (1 7), and a body coil for larger children (one). The

smallest coil into which the child would fit was always chosen, because our experience indicated that this produced the best image quality on SE studies of the chest, abdomen, and pelvis. All patients less than 6 years old were sedated; those less than i 8 months old received chloral hydrate (60-1 20 mg/kg) orally, and those between 18 months and 6 years received

Nembutal

(pentobarbital,

3-6

mg/kg)

IV. Patients

were

monitored

continuously

in

6i 8

HUBBARD

the imager via a digital pulse recorder and pulse oximeter. Coil size and sedation were the only variables in the performance of the

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examinations.

Ti -weighted SE sequences (500/1 5 [TA/TEl, four acquisitions, and 1 92 phase encodings) were obtained in the axial and coronal planes, and T2-weighted sequences (2000/90-120, two acquisitions, and 192 phase encodings) were obtained in the axial plane. Thereafter, two-dimensional sequential fast low-angle shot (FLASH) MR angiograms (25-50/10, 45#{176} flip angle, one acquisition, and 256 phase encodings)

were

obtained

in the axial

5 mm thick with a 20% overlap. was

frequently

flow

to evaluate

used

with

coronal

planes.

Slices

A third MR angiographic

presaturation

specific

and

vessels

were

sequence

of either the arterial or venous on the previous sequences. took 4 mm to perform, adding a

seen

Each MR angiographic sequence maximum of 12 mm to the examination time was 45-60 mm.

time. The total examination

The MR angiographic sequences were reviewed as raw data sets and processed after acquisition by using a maximum-intensity-projection algorithm. The SE images were reviewed first by the radiologists as a group and then used as a guide to evaluate the MR angiographic sequences. On Ti -weighted images, areas of tubular flow void that connected to definitive vascular structures were identified. The major vessels supplying or draining the liver (aorta, hepatic artery, portal vein, inferior vena cava, and hepatic veins) were identified. These

same areas were then evaluated on the angiographic sequences. The brightness vessel

of the signal within the vessels and the sharpness

of the

walls were evaluated. Respiratory or motion artifacts, such as

blufflng of the vessels and ghosting, were noted. Visibility of the major vessels with MR angiography was graded as equal to, better than, or worse than that on the SE images. The presence of either portosystemic collateral vessels or tumor vasculanty was also determined for both MR angiographic and SE techniques.

ET AL.

AJR:159,

September 1992

nant hepatic tumors. In six examinations, lange vessels coursing through and around the tumor were seen on MR angiography only. MR angiography showed occlusion of major yes-

sels

in three

examinations.

One

of these

patients

had

preoperative arteniognaphy, which showed the same findings (Fig. i ). One patient had cavernous transformation of the portal vein caused by tumor invasion of the porta hepatis (Fig. 2).

MR angiography of patients before

was useful in two liver transplantation.

of seven examinations The MR angiogram

showed the presence of portosystemic collaterals (Fig. 3) in both cases and a replaced hepatic artery in one. MR angiography showed flow in the portal vein in all seven examinations. Images obtained after processing sity-projection algorithm were not resulted in a confusing overlap of intensity projection was occasionally contiguous slices were reformatted

with the maximum-intenbeneficial because they vessels. The maximumhelpful when only a few together. The most useful

vascular information was obtained from the axial and coronal raw data images from the MR angiognams. Respiratory and motion artifacts were present on all MR angiognaphic blurring (two

sequences and ranged from mild to severe patients) of the vessel walls. Ghosting artifacts

of the aorta were most prominent

in children

old. This was eliminated

on sequences

arterial flow. Respiratory

artifacts

dome

less than 2 years

with

presatunation

were most prominent

of

at the

of the liver.

Discussion

MR is being used increasingly in the evaluation of abdominal diseases in children [9]. Liver tumors are the third most

Results Overall,

visualization

of major

vessels

(aorta,

celiac

artery,

hepatic artery, inferior vena cava, portal vein, and hepatic veins) was better with MR angiography than with SE Sequences in 12 cases (60%), equal in five (25%), and worse in three (1 5%). In the eight studies in which the quality of vessel visualization on MR angiograms was graded equal to or worse than that on SE images, all the patients were less than i year old. Additional vascular information was obtained with MR angiography

vascular

in i 0 of 20 cases.

In two patients,

this additional

was obtained even though the overall had been rated as equal to on less than that of the SE images. One patient with hemangioendotheliomas and congestive heart failure had an MR angiogram that showed marked quality

dilatation

information

of the

MR

angiograms

of the hepatic

artery

and

hepatic

veins.

The

MR

angiogram helped to differentiate the dilated hepatic artery from the portal vein. These large vessels could not be differentiated on SE images. An abdominal arteniogram obtained before embolization of the hepatic artery confirmed the anatomy of the major vessels seen on the MR angiogram. However, arteniography also displayed collateral vessels to the tumors from the superior mesentenic artery and intercostal arteries that were not shown by MR angiognaphy. MR angiography showed surgically important vascular structures in seven of 1 0 examinations of patients with malig-

common

intnaabdominal

neoplasms

in childhood.

Approxi-

mately two thirds of these tumors are malignant. The remainden are due to vascular malformations or benign tumors [1 0]. The primary treatment of malignant hepatic neoplasms in children

is complete

surgical

resection

of the tumor.

Con-

sequently, preoperative assessment of vascular and sectional anatomy of the liver is important. Some investigators maintain that conventional angiography is still required for presurgical planning for such patients [1 1]. However, MR angiography combined with SE sequences made conventional angiography

unnecessary patient,

in all but one of the patients

an extremely

large

tumor

with

in our series. In that possible

occlusion

of

the portal vein was found in the region of the porta hepatis, and angiography did not provide any more information than MR imaging did. MR imaging can be useful in differentiating hepatic hemangiomas from other nonvascular tumors of the liven [12, 13]. Children with hemangioendotheliomas of the liver may have

congestive through

heart the

tumors.

failure

caused

Embolization

by excessive of the

hepatic

blood

flow

arteries

can

be performed

the

if drug and other therapies fail [i4]. Although combination of MR angiography and SE imaging can

show the hepatic lization, visualize

arterial and venous

anatomy

before embo-

the resolution of MR angiography is not adequate to small collateral vessels. In the one child who had

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AJR:159,

September

MR

1992

ANGIOGRAPHY

OF

LIVER

DISEASE

IN CHILDREN

619

Fig. 1.-I-year-old boy with hepatoblastoma. A, Axial Ti-weighted MR image shows large hepatoblastoma (straight arrows) in liver displacing hepatic artery (curved arrow). B, Coronal MR angiogram (maximum-intensity projection) shows occlusion of inferior vena cava (curved arrow), which refills via collaterals at hepatic veins (arrowhead). Large collateral vein (open arrow) on surface of tumor and multiple small collaterals (straight solid arrows) course around periphery of mass. C, Axial TI-weighted MR image obtained after 6 months of chemotherapy shows clot or slow flow in inferior vena cava (arrowhead). Note tortuous vessel (large arrow) parallel to portal vein (small arrow). D, Axial MR angiogram shows flow in inferior vena cava (open arrow) and portal vein (straight solid arrow). Tortuous vessel (curved arrow) Is a collateral vein connecting portal vein and superior mesenteric vein. E, Axial MR angiogram shows occlusion of right portal vein (curved arrow) by tumor (straight arrows). F, Late phase of superior mesenteric digital angiogram confirms occlusion of right portal vein (curved arrow) and presence of a collateral vein (straight arrow) connecting superior mesenteric vein and portal vein.

arteniography before embolization, systemic collateral vessels from the superior mesenteric and intercostal arteries were

onstration

detected that were not seen on MR angiograms or SE images. Conventional angiography is still required to plan embolization procedures in these children.

lies are common (1 4%) [20]. In children with extrahepatic biliany atresia, detection of a preduodenal portal vein or azygous continuation of the inferior vena cava before surgery is

Sonognaphy

remains

the primary

method

liver and its vasculatune

before

[i5]. Early angiography

work [1 6] has in the examination

investigational can be useful

liver disease

for evaluating

transplantation

the

in children

shown that MR of patients with

and portal hypertension. MR angiography is portal vein thrombosis, vanices [i 7], and dynamic flow within the portal system [i 8]. Demonstration of portal vein patency and vanices is important, as is the demaccurate

in showing

with

of normal

liven disease,

important.

vascular

hepatobiliary

Although

these

anatomy and

vascular

other

[1 5, 19]. In children congenital

anomalies

are

considered a contraindication to transplantation, of these variants allows preoperative planning grafts [21]. In two

of our examinations,

portosystemic

anoma-

no longer

knowledge of vascular

collateral

vessels

and

subcuta-

(short

gastric,

coronary,

gastroesophageal,

neous These

vanices) vessels

were displayed only on MR were not observed on previous

angiognaphy. sonognams.

HUBBARD

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620

ET AL.

AJR:159,

September

1992

Fig. 2.-6-year-old boy with hepatocellular carcinoma, after 6 months of chemotherapy. A, Axial MR angiogram shows cavernous transformation of portal vein (straight arrow) caused by tumor in perth hepatis (curved arrows). B, Coronal MR angiogram (maximum-intensity projection) also shows cavernous transformation (arrow) of occluded portal vein.

Fig. 3.-2-year-old drome and liver failure

boy with short-gut syncaused by chronic hyper-

alimentation. A, Axial Ti-weighted MR image shows dilatation (arrow) of splenic vein. B, Axial MR anglogram shows dilated tortuous splenic vein (open arrow) with portosystemic (lqrge solld arrows) and cutaneous collateral (small solid arrows) vessels not seen on SE images.

Vanices associated with portal hypertension may be difficult to see on sonograms because of overlying bowel gas. Bowel gas did not obscure the portal on mesenteric anatomy on MR angiograms in any of our patients. Preoperative knowledge of the existence of such collatenals in patients with portal hypertension or large tumor vessels in patients with neoplasms enables more careful surgical dissection. Respiratory artifacts on the MR angiognaphic images were most prominent in children less than i year old. This probably reflects the higher respiratory rate of young children. Motion

mation, superior

artifacts

patic vasculatune in children respiration will also improve.

on MR angiognaphy

dome, causing blurring of junction. This area of the images. Ghosting artifacts were also most prominent can be eliminated by using The method used in our grams

and SE images

was

were

most

prominent

at the liver

the hepatic veins and cavoatnial liven was seen better on the SE from pulsatile flow in the aorta in younger children. This artifact presaturation of arterial flow. study to compare the MR angionot blinded,

and,

collateral vessels seen on MR angiognams were not identified, on SE images. Although sagittal

in this study,

they may provide

regarding the origins of the celiac and arteries. In conclusion, although artifacts caused by respiratory motion were present on many of our MR angiognaphic images, these artifacts did not interfere with the diagnostic usefulness of the examinations. Additional vascular information was obtamed with MR angiography in 50% of cases. As shorter TRs and TEs lead to faster imaging techniques, and as methods for motion compensation, gradient-moment nulling, and

phase-encoded

reordering

improve, who

the demonstration are

unable

of he-

to

suspend

and

academic

AJR

1990:155:

ACKNOWLEDGMENTS We thank

support

Ken

Fellows

for editorial

suggestions

and Valerie Tsafos for secretarial

help.

consequently,

some bias may have been introduced. The method of grading the quality of images was quite subjective. Nonetheless,

not obtained

particularly mesentenic

sought, but scans were

additional

infon-

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JM, Armstrong

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E, Smith

T. Imaging

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AJR:159,

September

1992

MR

ANGIOGRAPHY

OF

LIVER

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consideratransplansyndrome:

Diagnosis of liver disease in children: value of MR angiography.

We retrospectively studied the clinical use of MR angiography, a gradient-echo technique susceptible to motion, in the preoperative evaluation of the ...
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