Digital Images with Fuji Computed Radiography (FCR) in Dento-Maxillo-Facial .Radiology

Takenori NOIKURA, D.D.S. Ph.D., Shigeaki SUENAGA, D.D.S.,

Tsuyosh i SATO, D.D.S., K a z u n o r i K A W A N O , D.D.S., Mich iyo F U J I M U R A , D.D.S.,

Yasuh iko M O R I T A ,D.D.S. and Youich i ro I W A S H I T A , B.Sc.

Dept. of Dental Radiology, Kagoshima University Dental School, Kagoshima, Japan.

(Received : Oct. 25, 1985, Accepted : March 5, 1986)

Key Words : Digital image, Fuji Computed Radiography (FCR), Dento-Maxillo-Facial Radiology

Summary A digital radiographic system utilizing scanning laser stimulated luminescence (FCR) is

used in pantomograms, tomograms of TMJ, cephalograms, sialograms and soft tissue radiograms. FCR

provided the high quality images which were easy to interpret. In particular, with tomograms of TMJ,

images of soft tissue were obtained, holding out the possibility of successful diagnosis of TMJ

dysfunction.

Over the past few years advances in

computer image processing have led to a

corresponding increase in the use of digital

imaging for radiographic diagnosis. Fuji

Computed Radiography (FCR) is a new

system which uses a process known as

"scanning laser stimulated luminescence ''1'2'3>.

The main advantages of this system are that

it provides images of wide visibility and

latitude and of consistently high quality, and

that it makes radiography at low exposure

doses possible '). FCR is already being used in

chest radiography, bone and joint-radiogra-

phy, digestive radiography, in subtraction

angiography, pelvimetry and also in pediatric

t racheography and soft tissue radiography

which need wide latitude. In all these areas it

is becoming well known for its ability to

produce images of high diagnostic valueS<

This paper presents our opinion on the

diagnostic value of FCR in the maxil lo-facial

regions. We should like to thank Department

of Radiology at Kagoshima Universi ty

Medical School for the use their FCR.

Material and methods

Instead of a conventional film screen

system, FCR uses a special image sensor

which has an imaging plate of wide dynamic

range. The basic constituents of the FCR

system are shown in Fig. 1. In addition to a

conventional X- r ay equipment, there are four

new units: a ) an image sensor, b ) an image

reader, c) an image processor, and d) an

image recorder. Since the details have al-

ready been published I'a3'5), a basic outline of

Oram Radiol. Vol.1 No.2 1985(107~115) 1(107)

XGRay

Imaging , Image Plate Reader

Fig. 1. Basic block diagram of FCR.

Image Processor

I Digital Memory

, hnage , Computed Recorder Radiographs

each unit is given as follows.

a ) Image Sensor: Instead of the usual

radiographic film, the FCR system uses what

is called an imaging plate (IP). This consists

of a polyester support covered with BaFX

crystal to a thickness of 300 um, the total

thickness being just under 1 mm. When

exposed to X-rays, energy is stored in the

crystal, and when the crystal is scanned by a

He -Ne laser beam, the stored energy is given

off as luminescence. Residual energy can be

easily erased by flooding the IP with normal

white light, and the same IP can then be used

again.

b ) Image Reader: The image reader reads

the IP by scanning with a laser beam, as

explained above, and then converts the X- ray

image into digital electric signals. And the

resulting digital signal is sent to the image

processor.

c ) Image Processor: The image processor

takes the digital signal from the image reader

and performs such tasks as contrast enhance-

ment, spatial frequency enhancement, sub-

traction and addition, according to the needs

of the user.

d ) Image Recorder: The image recorder first

takes the digital signal f rom the image

processor and converts this into a H e - N e

laser beam with a 10-bit d ig i t a l / ana log

converter and a light converter, and then

with this laser beam records the image on a

special silver chloride film. In this process, 14

x 17 inch and 14 x 14 inch images are reduced

to half-size, 10 x 12 inch images to two-thirds

of the original, and 8 x 10 inch images are

recorded full size. The resulting film is

developed by an automatic processor in 3

minutes.

The FCR is generally used to produce

two images at the same time: one using the

contrast enhancement which results in an

image not dissimilar to the conventional

screen-film images: the other using enhance-

ment of a particular frequency band to give

an image of the enhanced spatial frequency.

Results

For the clinical application of FCR in the

max i l l o - facial regions, the following pro-

jection methods can be used in the extraoral

radiography. The following is a description

of several cases of extraoral radiography

conducted in accordance with the conditions

prevalent at the Department of Radiology,

Kagoshima University Medical School. In

FCR using contrast enhancement, the char-

acteristic curve chosen was similar to that

of conventional film; and in FCR using the

spatial frequency enhancement, frequencies

in the vicinity of 0.75 c / m m were empha-

sized.

1 ) Panoramic radiography

Since no panoramic imaging plate for

FCR is available at the moment, a panoramic

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Fig. 2. Images performed by two different types of image procedures. A: contrast enhancement B: spatial frequency enhaneement(0.75eycles/mm) Ameloblastoma

radiogram was achieved by combining a 10 x

12 inch plate with an IP pack using Siemens

OP 5. Of the two FCR images (Fig. 2, A and

B), the image obtained after contrast enhance-

ment was similar to that obtained from the

conventional screen-film systems (A) ; where-

as in the images obtained by the spatial

frequency enhancement there was an "edge

effect" whereby the borders were emphasized

and thus easier to discern (B) . The anatomi-

cal structure and trabecula of areas such as

the TMJ region, maxi l lary sinus, nasal

cavity, and anterior tooth regions were

shown clearly. The margins of lesions and

shape of the remaining bone fragments could

by clearly made out (Fig. 3). The depiction of

fracture lines and calcified mass in soft tissue

were also outstandingly clear (Fig. 4, 5).

With the images which had had the spatial

frequency enhancement there was a linear

radiolucency due to the "edge effect". This

could be mistaken for secondary caries.

However, this linear radiolucency could not

be seen in the images which had had the

contrast enhancement.

2 ) Tomography of temporomandibular joint

The use of the FCR was extremely

effective in tomography of the temporoman-

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Fig. 3. Pleomorphic adenoma infiltrated to mandible ramus.

Fig. 4. Fracture of mandible.

Fig. 5. Phlebolith.

4(~10)

Fig. 6. Articular soft tissue im- Fig. 7. Articular soft tissue ima- Fig. 8. age: normal pattern, age: Type A(resembling

anterior meniscus dis- placement with reduction)

Articular soft tissue im- age: Type B(resembling anterior meniscus displa- cement without reduction)

Tab. 1. Correlation of articular soft tissue images and cilinical symptoms

Pain Clicking Locking Total

Normal 14 29 13 56 Type A (Meniscus displace-

ment with reduction) 3 31 2 36

Type B (Meniscus displace- _ _ 12 12 ment without reduction)

Total 17 60 27 104

Tab. 2. Comparison of bone changes between FCR and convetional radiography

FR>CR FR CR FR<CR

Erosion Eburnation Marginal proliferation Deformity Flat tening

5 4 1 - - -- i 2 12 4

Concavity

1 1

Total

11 20 1

Total 6 5 3 12 4 2 32

FR: Fuji Computed Radiography CR: Conventional Radiography

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dibular joint. Articular soft tissue, which

previously could only be observed through

arthrography of the temporomandibular

joint, was observed in FCR images which had

had the spatial frequency enhancement. In

taking simultaneous radiograms of the bone

structure and articular soft tissue, we found

that the best results were obtained from

narrowing the field to 5 cm diameter of the

IP's surface and using a tomographic angle of

16 ~ . The images of articular soft tissue of the

mouth open and closed, showed abnormality

of location and shape between the anterior of

the condyle and the articular eminence. The

images of soft tissue which were obtained in

this way were divided into three types:

normal (Fig. 6), Type A similar to meniscus

displacement with reduction (Fig. 7), and

Type B to displacement without reduction

(Fig.8). Tab. 1 shows the relation between

these soft tissue images and clinical symp-

toms. Simultaneous analysis of the bone

structure was possible showing minute

changes in the cortical bone and trabecula

(Tab.2).

3 ) Cephalography

Recently cephalograms have been used

ont only in orthodontic t reatment but also in

many other fields, and there is now a demand

for the radiographic analysis of soft tissue

together with hard tissue. There is also a

demand for lower exposure doses so that

younger subjects can have regular X- ray

diagnosis. The following are the results of

our experiments using a skull phantom model

and spatial frequency enhanced images. ( i )

FCR depicted both hard and soft tissue, and

by using a filter for the profile, soft and hard

tissue could be seen clearly even at a low

dose. ( ii ) The orthodontist 's errors in setting

the landmarks were reduced to 1 / 8 com-

pared with the conventional cephalograms.

(iii) In setting the landmarks and in obtain-

ing images of good general quality, the

radiation doses were only 1 / 3 of the con-

ventional cephalograms. It thus appears that

FCR produces the images of high resolution

Fig. 9. Cephalogram of routine exposure dose showing profiles of face and bone image simultaneously.

Fig. 10. Cephalogram obtained with 1/3 dose of Fig. 9. revealing no significant image quality deterioration.

6(z z2)

(Fig. 11).

5 ) Soft tissue radiography

The latitude of FCR is such that slight

changes in soft tissue tumors are shown up

very clearly, and because of the wide dyna-

mic range of the system, both soft tissue and

bone can be observed at the same time (Fig.

12, 13).

Fig. 11. Sialogram of parotid gland showing fine arborization.

Fig. 13. Dermoid cyst in floor of mouth.

Fig. 12. Lymphangioma involving tongue and submental region delineated clearly from surrounding structure.

in both hard and soft tissue at low exposure

levels (Fig. 9, 10).

4 ) Sialography

With the conventional screen-film sys-

tems it has been difficult to interpret the

areas where bone and soft tissue have

overlapped, but with FCR this is now pos-

sible, and the glands are also shown in detail

Discussion

The clinical use of FCR in the maxil lo-

facial regions has just begun, so it is difficult

to state anything with certainty. However, a

few facts could be noted.

The Contrast enhanced radiograms were

found to be similar to the conventional

radiograms, while the spatial enhanced

radiograms were similar to xeroradiograms.

In addition, owing to the "edge effect", the

images which had had the spatial frequency

enhancement were much clearer than with

the conventional screen-fihn system, and the

depiction of anatomical structure, trabecula,

the margin of tumors, and calcified mass in

soft tissue overlapping bone was vastly

superior. Also with bone and intraosseous

lesions the details which could not be seen in

the conventional radiograms were easily seen

z(lis)

by using FCR. In other words, image pro-

cessing is giving clearer radiograms thus

reducing the risk of misinterpretation of

radiological information.

However, the spatial frequency resolu-

tion of the 10 x 12 inch IP is only 2-2.5 c /

mm, and in the high frequency band there is

some noise, so in the interpretation of the

minute details of bone trabecula FCR is still

inadequate. Improvements of spatial resolu-

tion and magnification were tried ~>, but

further improvements in the equipment and

in the IP are expected. With the spatial

frequency enhanced images, linear radiolu-

cency owing to the "edge effect" was ob-

served particularly around the metal crowns,

and this could be mistaken for secondary

caries, but when the contrast enhanced

images were also used, a precise diagnosis

was possible. We found that creating images

by these two methods from one radiogram

gave reliable results.

Since FCR uses an IP of wide dynamic

range, it is possible to get good results from

simultaneous radiograms of soft and hard

tissue. In the radiograms of the temporoman-

dibular joint, articular soft tissue of the TMJ

could only be observed in arthrography

previously. However, in tomography of

theTMJ using FCR, the images of articular

soft tissue can be obtained without using a

contrast medium. An improvement in the X-

ray diagnosis of TMJ dysfunction could be

expected by this new technique.

One of FCR's greatest advantages is said

to be the high resolution images which can be

obtained from low radiation exposure levels.

This time we tried only for cephalography at

low radiation levels, and we found that

adequate cephalograms of bone margins

could be obtained at low doses by increasing

the edge effect. In the conventional detailed

radiography of the internal structure of

bones and lesions, radiological information

decreases in proportion to the decrease in X-

ray exposure. However, with FCR a consider-

able decrease of exposure is possible without

a loss of information.

In FCR, because the computer processes

the signal, even if the exposure factor is not

ideal, the final image can be of a high quality.

This is extremely useful in clinical practice.

The routine image procedure does not

necessarily give the optimal results for every

case, and there still is a need for more

experience of using FCR clinically in a

greater number of cases and with better

projection methods suited to each type of

disease and diagnosis requirement.

We have discussed our findings on the use

of FCR in the maxillo-facial region. The high

quality images which were easy to interpret

were obtained. With the tomograms of the

temporomandibular joint, the images of soft

tissue were obtained, holding out the poS-

sibility of successful diagnosis of TMJ

dysfunction from the radiographic images.

Also the high resolution cephalograms were

taken at low radiation exposure levels.

We hope that an increase in case

material will lead to more progress in

diagnosis by FCR, and we have no doubt that

FCR will prove to be a valuable tool in

radiological diagnosis.

Acknowledgment: We would like to

thank Shinji Shinohara, Profassor of Dept. of

Radiology, Kagashima University Medical

School for allowing us to use the FCR.

References

1) Takano, M.: New Computed Radiography; Fuji Intelligent Diagnostic X-ray Systems. Image technology & Information display (Medical) 14

8(114)

(6): 409-413, 1982. 2) Takano, M.: New Computed Radiography

Utilizing Scanning Laser Stimulated Lumines- cence. Jpn. J. Clin. Med. 41 (7): 1395-1403, 1983.

3 ) Sonoda, M., Takano, M., Miyahara, J. and Kato, H.: Computed Radiography Utilizing Scanning Laser Stimulated Luminescence. Radiology 48: 833-838, 1983.

4 ) Hachiya, J., Korenaga, T., Miyasaka, Y., Nitatori, T., Wakasa, K. and Furuya, Y.: Computed Radiography Utilizing Photostimulable phoshor. Igaku no Ayumi 127 (14): 1199-1206, 1983.

5 ) Tateno, Y., Editor: Clinical significance of FCR. J. Medical Imagings 4 (Suppl.): 1-135, 1984.

Reprint requests to :

Takenori NOIKURA, D.D.S., Ph. D. Dept. of Dental Radiology, Kagoshima university Dental School 1208-1 Usuki-cho Kagoshima, Japan

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