approximately 10 cm from the surface of the phantom. The phantom was scanned sequentially until the cross section of the syringe was seen. After

sultant needle.

this,

0 #{176} - 1 80 0 with the cidence distance and the

a point

of entry

electronic were used the center entry. The formed by this

line

was

were

then

obtained

the computer software. the angle of incidence distance,

the

biopsy

inserted using direct it to the The phantom locate

the

chosen.

needle

Lung:

of

wasthen device

to

then

and

rescanned

determine

Spiral

the

Twenty passes were made randomly chosen angles of inwithin this range. The average between the point of entry center of the target was 10 cm.

device

To hit a lesion depth of 10 cm,

±3#{176} is needed.

to me-

the

were angle

1 cm in diameter at a an angle of tolerance of

Seventeen within of entry

remaining

Volumetric

was

who

underwent

opsy.

Electronic

draw

a line

used

on

14 patients

CT-guided calipers

needle were

connecting

bi-

used

the point

to

of en-

try on the skin to the lesion. The cornputer software then stated the length and the angle to the horizontal of this line. With use of the distance to the lesion and the angle of incidence, the de-

was used

to guide

the needle

to

the lesion. The resultant angle formed by the needle shaft to the horizontal

Results

passes pated

target.

was

of

The

vice

On the basis of and the desired

the guidance

of the with

of

by using

needle

formed by the shaft angle was compared

the expected angle. The angle to the horizontal was varied within a range

The

calipers of the computer to draw a line connecting of the target to the point angle to the horizontal this line and the length

angle This

of the 20

±3#{176} of the anticiof the needle, and

three

were

CT with

within

was within angle guides curacy.

±3#{176} from

the anticipated

of entry. This device, therefore, the needle with reasonable acU

±5#{176}.

Single-Breath-Hold

Technique

Peter Vock, MD Martin Soucek, MD Martin Daepp Willi A. Kalender, PhD The authors adapted the transport systern of a computed tornographic (CT) scanner with continuous rotation capability to examine complete lung subvolurnes during a single breath hold. Twenty-four adult patients underwent scanning with up to 12 continuous 1-second rotations, and data acquisition was synchronized with longitudinal patient motion at one section thickness per second. Interpolated planar raw data were obtamed retrospectively from any level within the volume, and these afforded high-quality images that were comparable to standard images. Solitary puirnonary nodules were not omitted, their centers could always be depicted, and secondary reformations as well as threedimensional reconstructions were obtamed easily. The authors conclude that spiral volumetric CT, by completely surveying a subvolume of the lung, is an attractive new application of CT. Index terms: age quality technology

Radiology

tomography tomography 60.1211

(CT), im(CT),

1990; 176:864-867

of Diagnostic RadiolCH-3010 Berne, Switzerland (P.V., M.S., M.D.) and Siemens Medical Systems, Erlangen, Federal Republic of Germany (W.A.K.). From the 1989 RSNA scientific assembly. Received December 29, 1989; revision requested March 12, 1990; revision received and accepted May 1 . Address reprint requests toP.V. C RSNA, 1990 1

ogy,

864

From the University

Computed Computed #{149} Lung, CT,

#{149}

Department of Berne,

#{149} Radiology

M

1-2-second computed tomogmaphic (CT) scanners high-quality cross-sectional ODERN

ford ing

of pulmonary

ease

processes.

structures

Thin-section

mize volume averaging become the preferred

and

afimagdis-

scans

mini-

and have method for eval-

uating fine parenchymal structures (14) and detecting and characterizing pulmonary nodules (5-8). Specifically, high-resolution (“bone”) algorithms and targeted reconstructions offer im-

proved

image

quality

(2,3).

However,

the problem of reproducing consistent inspiratory levels for successive scans to obtain an anatomically continuous study persists (9). Scan localization, while less important in diffuse pulmonary disease, becomes crucial in focal disease. For both

adequate

characterization

and

densi-

tometry, sections must cut through the center of the lesion (5-7). With repeated suspended respiration, one may double-scan or omit specific levels and, despite acquisition of theoretically continuous sections, miss the center of the lesion (9) or even an entire pulmonary nodule. Furthermore, secondary refommations of the chest seldom have been useful

due

to

umes. Scanners measurements era! 1-second

irreproducible

lung

allowing continuous of one level during rotations have been

vol-

sevintro-

duced recently. We developed pothesis that a spiral scanning try based on longitudinal table with simultaneous tube rotation enable the study of a complete ume within the lung during a breath hold. This would allow

the hygeomemotion might subvolsingle us to

achieve anatomically continuous ning to avoid omission of levels

scanand to

retrospectively select the center of a solitary pulmonary nodule. The technical aspects of the new application are presented elsewhere (10). This project designed to demonstrate the clinical feasibility of spiral volumetric CT of the lung.

was

Materials

and

Of 170 patients

Methods referred

for CT of the

chest during a 3-month period, 24 patients (age range, 19-88 years; mean, 54 years) were studied with spiral volumetric CT; 17 were men, seven were women. Inclusion criteria were local-

ized

lung

diseases

for which

(a) region-

al targeted rescanning after initial screening chest CT was necessary to improve the information between 5cctions (n = 5), (b) initial contrast-material enhancement of mediastinal or other soft tissues was suboptimal (n 10), or (c) the center of a pulmonary nodule or the extent of a localized disease process

September

1990

a. Figure

solitary man

with

1. Spiral volumetric CT scans of a nodule (arrows) in a 45-year-old (12-second scan of a 24-mm subvolume 170 mA, 2-mm section thickness, 2-

mm/sec

table feed). (a) Selected spaced

images

ous

sequence

Both

2 mm apart obtained

at

the pulmonary

fion algorithm) (standard

subset

from 1-mm

windows

intervals.

(high-resolu-

and the soft-tissue

algorithm)

of

a continu-

windows demon-

continuously

strate

the nodule and its relation to the pleura. Results of the two fine-needle aspiration biopsies were negative for a diagnosis of cancer. infectious

Inflammatory granuloma,

cells, were

probably found

due to at biopsy.

(b) Two sagittal

reformations, limited by the volume of only 24 mm, demonstrate the nodule and its contact to the pleura with smooth contours. (c) Three-dimensional resmall

construction,

proves

with

a view

the demonstration

ic relation between and the pleura.

had been shown incompletely by several thin-section high-resolution CT sections (n 9). Inability to suspend respiration

for

at least

8 seconds

was

the criterion for exclusion. Three patients had lung cancer, nine had lung metastases, five had benign mass Icsions, and seven had localized nonexpansive

Initial Volume

benign

lung

disease

(Table).

single-section

CT consisted

176

3

#{149} Number

of

above,

im-

of the topograph-

the nodule,

8-mm collimation). high-resolution

c.

b.

from

scans

Several were

both

vessels,

additional obtained

in

10-mm-thick sections through the chest spaced at 10- or 15-mm intervals to search for neoplastic or other disease, respectively, with scan parameters of

nine patients with Our commercial

137 kVp,

forms up to 12 continuous 1-second motations at 170 mA or up to 5 rotations at 250 mA. For spiral volumetric CT, we used an experimental setup with a

230

mA,

and

1-second

scan

time. Thirteen patients also underwent a regional dynamic contrast materialenhanced study with acquisition of contiguous 1-second scans (11 patients with 10-mm collimation and two with

Plus;

Siemens

en, Federal

modified nism.

Medical

Republic

integrated Scanning

2-mm collimation. scanner (Somatom

was

Systems,

of Germany)

table-feed synchronized

Radiology

Emlang-

per-

mechawith #{149} 865

longitudinal table motion, as used for scout views, at a speed of one section thickness per second (10). Depending on the clinical problem, a section thickness of 2 mm (n = 10), 5 mm (n 2), 8 mm (n = 4), or 10 mm (n 8) selected, and therefore the speed of table feed was 2-10 mm/sec accordingly, mostly for a 10-12-second scanning time. Before the patient left the gantry,

was

noncomrected

1-second

constructed

immediately,

responding second)

were

each).

me-

the cor-

data (one each from the im-

to the hard

for

were

and

helical raw transferred

age processor seconds

images

Later,

disk

(about

40

postpmocessing

included interpolation of adjacent helical maw data to retrospectively synthesize nondistorted planar raw data for arbitrary table positions (to 1-mm intervals) within the volume (10). Subsequent calculation of images was performed according to the clinical prob1cm

for

any

field

center, and algorithms.

of view,

with standard Thus, under

any

section

and/or bone the current cx-

perimental condition, a 12-second penod of spiral volumetric CT required about 8 minutes of immediate processing and up to 30 minutes of delayed postprocessing under time-sharing conditions.

diseases

could

be detected

with

cystic

quality

had

spiral

volumetric

significant

soft-tissue with lung artifacts

streak

windows windows, were

no

was judged identical CT scan (b)

spiral

volumetric

The

demonstration

for a single

section

ventional from

CT. Secondary

spiral

smoother

contours

CT scans

had

those

reforma-

than

tions obtained from a series section CT scans. Similarly mensional reconstructions

the demonstration

and

results

demonstrate

of spiral

CT is at least

geometry

were

CT in

The

planar

problem

volumes

by

of inconstant

with

repeated

sus-

2) or thicker

nizing

of up

to 10 mm

were

selected, the quality of spiral volumetCT scans was at least equivalent to

nc that

obtained

technique

with

the

conventional

in the demonstration

lesions and summarizes

CT

of both

normal anatomy. The Table the results of the qualita-

tive comparison between spiral volumetric and conventional CT. Four of the seven cases in which spiral volumetric CT quality was superior were observed ses. Five

866

in patients of the seven

#{149} Radiology

with lung metastacases occurred

and

Pugatch

and,

for contrast-enhanced poulos

et al (9,11). Both with intervals

scanners

subsequent

scans.

is based continuous

Spiral

Our

Raptoused

two

volumetric

on the new development measurement during

al rotations. feed

groups between

new

idea

scanning

with

continuous

overcomes

some

volumetric

breath and

hold

the

is limited

storage

capaci-

can

be continued.

Data

40 minutes

process-

per spiral

scan

present study will be reduced 10 seconds per image for image

to

reconstruction in the near future. The heat capacity of the tube, however, will remain the most severe hardware limitation of spiral volumetric CT of a large volume. Fortunately, a high x-ray current

is not

as critical

for

may

lung

other

trunk.

This

be the

reason image

for the excellent quality achieved

imaging

parts most

of the important

and consistent with spiral vol-

umetnic CT compared with ordinary CT scans. In some cases, the superiority of spinal volumetric CT scans seems to result mainly from the increased number

especially

studies,

one

as it is for imaging

data

pended respiration was realized and approached differently by the groups of Shaffer

to

to

removed

into

inherent

respiratory

present

of up spiral

equivalent

the

interpolation

in the about

CT. The antispiral scanning

adequately

of bronchiectasis

spiral

ty of the image processor. Postprocessing includes maw data transfer to the hard disk of the computer before a

the

volumetric

(a) and

heating

ing of about

volumetric

and minor whereas

during

by tube

study

on interpolated images. Spiral volumetric CT demonstrated the lesions in a continuous sequence, allowing morphologic analysis and differentiation of disease processes (Fig 1). As the images could be reconstructed for arbitrary table positions within the scanning volume, the center of a nodule could always be depicted. Whether thin sections of 2 mm (Fig ones

med

vessels, the pleura, lesions (Fig 1).

the study of a lung subvolume 12 cm. Lung scan quality with

linear (10).

CT scan

and

Spiral volumetric CT still has some disadvantages. Currently, the number of rotations and thus the volume exam-

of singlethree-diimproved

rela-

early

CT in a 61-year-old

anatomy

rent.

of the spatial

practicality

CT

single-section

of normal

CT”) proposed by Raptopoulos et al (11). The radiation dose is considerably reduced because we work at low cur-

reformations

volumetric

CT versus

high-resolution

among the 13 patients with whom 10mm thick sections were used at con-

Our

artifacts

longer

with

bronchiectasis.

that with single-section facts resulting from

Noncomrected

these

Image

Discussion

Results

with ones

man

2.

on both

of scans. They had to agree on whether spiral volumetric CT scan quality was inferior, equal, or superior to single CT scans of the same area.

scans

b.

Figure

tion between pulmonary

CT scan quality was assessed by two radiologists, who compared the degree to which pulmonary vessels, bronchi, and the morphologic details of pulmonary types

a.

CT of sever-

of synchrotable

of the previous

limitations. Spiral volumetric CT meduces the period of suspended respiration from an average of 42 seconds in “dynamic CT with a single breath hold” (9) to 12 seconds. At 2-mm collimation, spiral volumetric CT increases the volume surveyed from 12 to 24 mm. It affords a systematic examination of the selected volume and, therefore, is theoretically superior to the empiric repeated search (“to-and-fro dynamic

of closely sometimes morphologic

the ton did ed

spaced

images

available

allows analysis details. The

that

of more increase

of

effective section thickness by a facof up to 1.3 due to interpolation (10) not affect scan quality. In our limitexperience, breath holding for 10-

12 seconds does not seem to be a significant problem; however, our group did not include severely dyspneic or non-

cooperative The main

patients. advantage

of spinal

volu-

metric CT is the ability to continuously survey a lung subvolume. This avoids omission of nodules on other small pathologic changes. It allows netrospec-

tive reconstruction of any level within the volume, facilitating the demonstration

of the

center

of a solitary

pulmo-

September

1990

nary nodule for densitometny (5-8), but also improving the quality of secondary refonmations or three-dimensional demonstrations of pulmonary lesions. Spiral volumetric CT is fully compatible with the needs of high-resolution CT of the pulmonary parenchyma (13). Alternatively, several subsequent spiral volumetric sequences with 8-10mm collimation may be used in the futune to screen the complete lung, that is, to search for metastases. In conclusion, spiral volumetric CT of the lung is an attractive new application of CT that be implemented easily on any scanner with continuous rotation capabilities. It simplifies and often improves CT demonstration of small nodules, both for morphologic analysis and for densitometry of nonexpansive lung lesions. As a basis for

can

secondary

reconstructions,

spatial

will likely be applied other problems. U Acknowledgments: tinguished

CT

of Heinz

Jung

1.

EA, Naidich

DP,

Khouri

NF, Siegelman

55.

mography

of the

II_ Interstitial 2.

1985; Mayo

resolution 3_

disease.

1:54-64. JR. Webb Radiology

Murata

K, Khan

Optimization

1987; A, Rojas

to demonstrate

tune of the lung.

Invest

terms: Biopsies, (US), technology

technology #{149} Ultrasound

1990; 176:867-868

176

#{149} Number

3

the

fine

Radiol

10.

1 1.

struc-

1988;

23:170-175.

5.

Siegelman

55,

Khouri

NF, Stitik

12.

170:629-635. Zerhouni

nodule.

UTRASOUND

almost

AJR

organ

Leo

1980;

pencutaand

are performed region

in the proposed needle constant visualization

and

CT measurements nodules. J Comput 6:1075-1087.

Khouri

NF,

EA,

Stitik

FP,

Leo

FP,

Siegelman

to Enhance

times

on of the

path. al-

lows for the safe placement of the necdle tip within the target and selection of the least traumatic route. Materials

Leo

in-

Fish-

SS,

et

135:1-13.

body. Procedures range from percutaneous biopsy of large and small (