Technical Sacral Donna Elliot Derek

Foramina:

View

Magid, MD K. Fishman, MD R. Ney, BS

terms:

image

processing

Sacrum,

Computed

(CT),

sacroiliac.

1991;

of

178:573-574

transaxial

naphy

of and of on of

computed

(CT)

removes

tion

of

element

superimposition (eg, soft tissue, air, feces), which limits visualization the sacrum and sacroiliac joints (SIJs) plain radiographs. The advantages using this technique in evaluating

trauma,

tumor,

previously ted

on

infection

described

coronal

(1-3).

views

imaging,

memory,

tilted

crum dictates and coronal

orientation

by oriented

to

This

presents

method the

these

views

studies.

in

We

cases.

Radiology

all

our

studies

Russell

and

sacnal,

D.R.N.),

and

paedic

Surgery

(D.M.),

Department The

Johns

Medical Institutions, Baltimore. gust 2, 1990; revision requested revision received September tember 19. Department

Address reprint of Radiology,

Hospital. 600 N Wolfe c RSNA, 1991

Volume

178

to

St. Baltimore,

Number

#{149}

requests The Johns

the

selected,

and,

selection

oblique

by

dorsal

sacrum

trary (in

(Figs

oblique

plane

of

The

arbi-

2a).

as less which of

were

sacral

Interactive

(Figs

“neal-time”

lb.

image

Freestanding provide the standard

most

ic,

SIJ

obtained

study.

The

reproducibly (Figs

new imde-

visualized

1, 2).

comminuted

stroys

this

landmark,

pro-

sacral

trauma

de-

most

cases,

the axis can be estimated Si and the more distal

of

of Ortho-

tends

to be

sacral

fractures

countered cases.

Au6; Sep-

to D.M., Hopkins

21205.

all

cases,

views

multaneous foramina

1, 2).

In

have

in three the

provided

of S-i

proximal

We

sacral

cnum,

of

to S-3

and

patients, view

also

means

the of

informa-

a routine

of the and of and comcurved sa-

display

it is helpful in

to

true

be

able

frontal

to

review

views,

orthog-

onal to the actual anatomy of interest rather than to the long axis of the patient. This allows an easy overview of the cortical integrity of the paired foraminal

margins

fluid

and

fonamen,

and

of

tissue

densities

which

may

changes

in

within represent

tumor

enables

a rapid

tissue,

examination tent of the

of the cephabocaudal SIJs. In patients with

usual

curvature

crum

due

and

or

to

position

pelvic

the

each

on reactive

tilt,

adjusted

orientation

to

of the

Although

of

exun-

the

sa-

scoliosis,

dys-

match

body

of

be

niques

of

described

can

gram

CT

a Siemens

called

TIR

construction) to

be

selection oblique

from

gantry

tilt,

plane

topogram.

would

also

allow

sacral that obtained This

be matched

allowing

re-

oblique the

system.

can

exama pro-

initiated

topogram

a freestanding

axis

For

selected

of a reformatted axis matching

oblique

performed

(topogram

chosen

a lateral

tech-

Scanner,

allows

of

with

be

a free-

basic

scanner.

Plus

this

with the

a standard in

actual sacrum.

optimized

workstation,

with

the the

implementation can

standing

direct

by

oblique-

imaging.

This

technical

matting

refinement

of the

sacral

in

image

additional patient scanning diation dose, yet it greatly cral and SIJ image quality. it will already

of 50

matting SIJ.

be

useful

to

using

radiologists the

no

time on maimproves saWe believe who

two-dimensional

to assess

refor-

requires

are

refor-

sacrum

and

U

si-

the

paired

showed

a

length of SIJ coronal views did

trauma

enhance

simultaneous

structures

enoblique

excellent

visualization

greater cephalocaudal than conventional (Figs

with

2a).

fractures

our

in

between L5sacrum, which

even (Fig

such In

coronal

Hopkins

spared

in

Occasionally, but,

to by

workstations to manipulate

full series of transaxial, coronal, sagittal images simplifies review normal and pathologic anatomy provides easy orientation to and munication of the findings. In a and oblique structure such as the

planes

and

foundly

data

tion

ple,

me-

(4).

cases

computer opportunity

technique

pre-

foramina to the fron-

body

ib).

is easily

necalcu-

images

an oblique-transaxial pelvic ring image, paralleling the conventional radiographic inlet view, for improved assessment of pelvic ring integrity (Fig

plasia (such as dwarfism), or trauma, the freely selectable baseline landmark

all the data and reimage sets (Fig ib).

oblique “sacral face forward the

the

rapidly

10 seconds)

coronal

plane

a line

bisected paralleled

function

reoriented the three

original

sented views,”

la,

software

approximately

us-

process,

cephalocaudal

oblique-transaxial

2

was

a two-point

readily

(D.M.,

MD

(axial, coroas previously

Discussion

recent

Received September 17; accepted

interpo-

The landmark axis of orientation (proximal two-thirds of the spinal canal on midline sagittal sections) can be

Department

Science

the

Instrumentation

Use

performed

Morgan

Radiological

E.K.F.,

most

were

H.

or

were

two-dimensional sagittal) format

scnibed

is rou-

pelvic,

trans-

view remains available in the age sets as has been previously

itself.

reformatting

reviewed

All

the

sacrum

were

the images

canal

2b).

sa-

interest. fast

data

was drawn that longitudinally the canal and approximately

tal

Methods

oblique used

From

of

a simple, the

sa-

the transaxial in fact, oblique-

structure

of

and

Sacnal

I

the

axes

Materials

50

both are,

the

all

and

standard nal, and

The

de-

symmein the the

of

of reonienting

actual

tinely

of bilateral changes SIJ. However,

that views

article

further

NJ)

lated to provide consistent pixel sizing in the x, y, and z axes. A bicubic interpolation was performed by means of a Catmull-Rohm algorithm. The data were then displayed in a

lated and produced

been

Reformat-

provide

tail for assessment try of and pathologic cral foramina and normally

have

scanner Iselin,

femred on magnetic tape to an independent workstation consisting of either a Sun 3/ 180 or 4/280 computer (Sun Micnosystems, Mountain View, Calif) and a Pixar Image Computer (San Rafael, Calif). The tape was read on to Pixar

ing

tomog-

the

DRH Systems,

with 4-mm collimation at 3-mm intervals, 3 or 4 seconds scanning time, 230 on 310 mAs, and 125 kVp. At comple-

central OUTINE

a Somatom

Medical

described (4). This simultaneously and interactively displayed the transaxial, coronal, and sagittal images (Figs la, 2a). For sacnal reorientation, a central sagittal section best demonstrating the

337,1211

33.1211

Radiology

use

(Siemens

tomography

Joints,

#{149}

and

at CT’ with

Conventional transaxial computed tomography (CT) is superior to plain radiography in depicting the sacrum. Because of the shape and orientation of the sacrum, CT provides oblique views of the structures of interest. With easily reproducible landmarks and standard transaxial CT data, orthogonal image sets can be produced that provide a true en face orientation matching the obliquity of the sacrum. This allows optimal visualization of the paired foramina and of the sacroiliac joints for better assessment of trauma, tumor, or inflammatory disease. Index

Developments

this produces

References 1.

Magid D. Fishman EK. culoskeletal inflammation.

Magid

D, Fishman

raphy

of the

York:

Churchill

Assessment In: Scott

EK, eds.

musculoskeletal

Livingstone.

Computed system.

1987;

Radiology

of musWW Jr.

tomogNew

63-84.

.

573

b.

I

Figure

1. CT scans of a patient with biopsy-proved metastasis. Pais a middle-aged woman with fever, low back pain, negative radiographs, focally positive technetium-99m scintigrams, and history of lung cancer. CT was performed to localize scintigraphic finding and to characterize as infection versus metastasis, if possible. (a) Conventional transaxial image (top left) displays a discrete lytic lesion eroding the iliac side of the anterior left SIJ (arrow) with no evidence of soft-tissue mass or abscess. This is seen in coronal image as webb (lower left, arrowhead). The sagittal image (bottom right) displays the selected oblique axis. (b) The oblique display, with orienttient plain

ing

three-dimensional

views

(top

right)

also

flipped

to match.

The

coronal or sacral foramina image now demonstrates most of the sacrum and SIJ on one view (bottom left). Incidentally noted is the standard, routinely obtained pelvic ring view (top left), which is automatically produced when transaxial data are reoriented to the sacrab oblique. (c) Coned sacral oblique coronal image demonstrates the foramina,

with

both

of high attenuation left lytic lesion.

cerebrospinal

within

fluid

them

(arrow),

and

tissue

and

(nerve

the SIJ with

root) areas the focal

b. Figure

2.

CT scans

of woman

with

severe

sacral

trauma

and

posterior

pelvic

ring

disruption.

(a) Conventional

transa.xial

scan

obtained

at

bevel of 5-2 partially demonstrates fracture and pelvic ring asymmetry (top left). Coronal image (bottom left) shows marked cephalic displacement of left pelvis. Landmarks for sacrab oblique axis are destroyed but can be approximated on a sagittal (bottom night) image. (b) Cobbimated sacrab oblique coronal image provides more of a fracture overview by demonstrating, on one image, fracture involvement of multipie foraminab levels and hemisacral shift. High attenuation of cerebrospinal fluid is believed to be due to hemorrhage.

2.

Fishman

EK,

Magid

D,

Brooker

AF

Jr.

Sie-

gelman 55. Fractures of the sacrum and sacroiliac joint: evaluation of computed tomography with multiplanar reconstruction. J South Med Assoc 1988; 8:171-177.

574

Radiology

#{149}

3.

Magid

D, Fishman

EK.

Assessment

of

musculoskeletal trauma. In: Scott WW Jr. Magid D, Fishman EK, eds. Computed tomography of the musculoskeletal system. New York: Churchill Livingstone, 1987; 85-111.

4.

Ney JE.

DR. Fishman EK, Magid D, Kuhbman Interactive real-time multiplanar CT

imaging.

Radiology

1989;

170:275-276.

February

1991