Diagnostic imaging of diseases affecting the mandible with the use of computed panoramic radiography Isamu Kashima, DDS, PhD,a Kazunori Tajima, DDS,a Kousuke Nishimura, DDS,a Ryo Yamane, DDS,b Makoto Saraya, DDS, PhD,c Yuichi Sasakura, DDS, PhD,C and Masao Takano, MSd Kanagawa, Japan

KANAGAWA DENTAL COLLEGE

Computed panoramic radiography was performed on patients with bone cyst, osteomyelitis, gingival cancer, and fibrous dysplasia, respectively, to determine the best imaging procedure for disease processes affecting the mandible. Gradational enhancement images for detection of density changes and frequency enhancement images for detecting changes in the margin and texture were effective in aiding the diagnosis of diseases of the mandible with the use of computed panoramic radiography. (ORAL SURC ORAL MED ORAL PATHOL 3990;70910-6)

C omputed panoramic radiography (CPR) can be carried out by means of computed radiography (CR) processes to digitalize radiographic information and record diagnostic images.‘? 2 In CPR, an imaging plate is used as a sensor in place of film. The relation- ship between the amount of luminescence and the dose of X-ray radiation is linear over a wide range. As a digital imaging system, CPR permits free manipu- lation of output images. Specifically, the density and contrast can be adjusted by gradational enhancement, and specific spatial frequency areas can be enhanced by changing the frequency.

The principles and clinical applications of CPR have been previously reported by Kashima and coworkers,3, 4 who also performed visual and physical quantitative assessment of the bone trabecular pat- tern in patients with Down syndrome by means of this method. As a continuation of these studies, the rela- tionship between imaging conditions and the clinical diagnostic significance of CPR for disclosing diseases of the mandible was studied. Representative cystic, inflammatory, tumoral, and dysplastic diseases local- ized in the molar area of the mandible were selected for imaging by CPR.

aDepartment of Oral Radiology, bDepartment of Oral Diagnosis, and CDepartment of Oral Surgery, Kanagawa Dental College. dTechnology Development Center, Miyanodai Fuji Photo Film Company, Kanagawa, Japan. 7116119354

110

MATERIAL AND METHODS

To study a broad spectrum of bone diseases affect- ing the mandible, cases of cyst, osteomyelitis, gingi- val cancer with bone destruction, and fibrous dyspla- sia localized in the molar area of the mandible were selected. All subjects were studied by CPR. Two types of images were used, namely (1) gradational enhance- ment to produce images similar to conventional pan- oramic radiographs, and (2) frequency enhancement to produce edge-enhanced images similar to xerorad- iographs. Images were processed in the spatial fre- quency areas of 0.25, 0.5, 1 .O, and 2.0 cycle/mm.

Four (3,5,7, and 9) frequency enhancement ranks were used. On the basis of the linear gradation, the gamma value was changed in three stages, 0.6, 1.0, and 1.4, centered around a density of 1.2. For images using gradational enhancement, a low-frequency en- hancement rank (1.5) was employed, with a sigmoid type of gradation. Under these conditions of image processing, 48 images given frequency enhancement and 4 given gradational enhancement were obtained in each case for visual evaluation of the imaging of diseases of the mandible by CPR.

RESULTS

Fig. 1 shows the CPR gradationally enhanced im- ages in the cases of bone cyst, osteomyelitis, gingival cancer, and fibrous dysplasia. All these images were processed in a spatial frequency area of 0.5 cycle/mm. Fig. 2 shows the processing conditions for gradational enhancement, sigmoid gradation at a low-frequency

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Fig. 1. Gradationally enhanced CPR images in spatial frequency area of 0.5 cycle/mm. A, Case 1. Cyst in the left body of mandible. B, Case 2. Fibrous dysplasia expanding from the left mandible to the right pre- molar region. C, Case 3. Gingival cancer with bone destruction in the molar area of the left mandible. D, Case 4. Osteomyelitis in the molar area of the left side of the mandible (arrow).

enhancement rank (1.5). With the use of these parameters, the images resembled the conventional panoramic radiographs.

Figs. 3 to 10 show the CPR frequency-enhanced images and the processing conditions for the four cases. The frequency-enhanced images had the xero- radiographic characteristic of edge enhancement and differed according to frequency area. Images in the low-frequency areas (0.25 and 0.5 cycle/mm) were relatively coarse with enhancement of thick bony tra- beculae, whereas those in the high-frquency areas (1 .O and 2.0 cycle/mm) were dense with enhancement of fine bony trabeculae.

Spatial frequency areas of 0.25, 0.5, 1.0, and 2.0 cycle/mm were used in all cases. In Fig. 3, the image of the bone cyst shows a linear gradation (Fig. 4). The frequency enhancement rank increased in fibrous dysplasia (Fig. 5) and osteomyelitis (Fig. 9) also showing a linear gradation, with a constant frequency enhancement rank of 5.0 in all frequency areas (Figs. 6 and 10).

In the images of the gingival cancer case (Fig. 7), the frequency enhancement rank was controlled at a relatively low value of 3.0 in all frequency areas. However, the gradation of this image was linear, with a greater inclination (gamma) of the straight line (1.4 in the amount of rotation [GA]) than those in the re- maining cases (Fig. 8).

The tables compare the images given gradational enhancement (Figs. 1 and 2) with those given fre- quency enhancement (Figs. 3 to 10). With respect to the cyst (Table I), the outline of the cyst and the bor-

8 INPUT SIGNAL (EXPOSURE)

A

5 -

3 -

a

0.01 0.1 0.21 0.5 1.0 1.0 10.0

b SPATIAL FREOUENCY(wmm)

Fig. 2. Conditions for image processing by gradational enhancement. Sigmoid gradation (a), with a low-frequency enhancement rank of 1.5 (b).

I 12 Kashima et al. ORAL SURG ORAL MED ORAL PATHOL July 1990

Fig. 3. CPR images of cyst in specific spatial frequency areas with the use of frequency enhancement.

a0 I . INPUT SIGNAL (EXPOSURE)

D

-

Table I. Bone cyst

Diagnostic feature Gradational Spatial frequency

1 enhancement 1 enhancement

GA1.4

GA 1.0

GA 0.6

Outline of cyst + +++

Inside of cyst + ++ Cyst and root apex + ++ Cyst and cortical border + +++ Bone trabeculae around + ++

cyst Displacement of mandibular ++ ++

canal

I I

I

I

L

b 0.01 0.1 0.15 0.5 1.0 2.0 10.0

SPATIAL FREQUENCY C c/mm 1

Fig. 4. Image processing conditions for Fig. 3. Linear gradation (a). The higher the frequency, the higher the rank of frequency enhancement (b).

Scale: (+++) = Optimal visualization; (++) = Adequate; (+) = Poor but diagnostic; (0) = Unacceptably poor.

der area between the cyst and cortical bone were clearer in the frequency-enhanced image (Fig. 3) than in the gradationally enhanced image (Fig. 1, A). In addition, frequency enhancement illustrated other diagnostic features more sharply.

In fibrous dysplasia (Table II), the image given frequency enhancement (Fig. 5) showed extension of the disease and expansion of the cortical bone more sharply than the image given gradational enhance- ment (Fig. 1, B). In contrast, the latter image was su- perior to the first with respect to the clarity of fine bone trabeculations in the lesion.

In gingival cancer (Table III), the frequency- enhanced image (Fig. 7) was slightly superior to the gradationally enhanced image (Fig. 1, C) with respect to the diagnostic features of bone destruction and floating teeth. However, the two types were similar with respect to the remaining diagnostic features.

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Diagnostic imaging of diseases affecting mandible I I 3

Fig. 5. CPR images of fibrous dysplasia in specific spatial frequency areas with the use of frequency en- hancement.

Table II. Fibrous dysplasia

Gradational Diagnostic feature enhancement

Border of lesion + Root apex and lesion ++ Extension of lesion ++ Expansion of mandibular +

cortex Bone trabeculae around ++

lesion Root apex and lesion ++ Fine bony abnormality + Gross bony abnormality +

I Spatial frequency enhancement

+ ++ +++ +++

++

++ 0 0

Scale: (+++) = Optimal visualization; (++) = Adequate; (+) = Poor but diagnostic; (0) = Unacceptably poor.

In osteomyelitis (Table IV), the frequency-en- hanced image (Fig. 9) showed the alveolar crest more clearly than did the gradationally enhanced image (Fig. lo), but the two types of enhancement produced no differences in the remaining diagnostic features.

DISCUSSION

Although rotational panoramic radiography is per- haps the most common extraoral radiographic tech- nique used in dentistry, traditionally the images are not sharp because of the problem, inherent in tomog- raphy, of blurring. To obtain less blurred computed panoramic radiograms of high diagnostic value, we applied digital radiography to rotational panoramic

GA1.4

GA 1.0

GAO.6

a0 I .

INPUT SIGNAL (EXPOSURE 1

A B C o

I 0.01 0.1 0.25 0.1 I.0 2.0 10.0

b SPATIAL FREQUENCY(wmm)

Fig. 6. Image processing conditions for Fig. 5. Linear gradation (a). The frequency enhancement rank was con- stant at 5.0 for all spatial frequency areas (b).

114 Kashima et al. ORAL SURG ORAL MED ORAL PATHOL July 1990

Fig. 7. CPR images of gingival cancer in specific spatial frequency areas with the use of frequency enhancement.

A - GAl.4

B - GA 1.0

C - GAO.6

I + INPUT SIGNAL (EXPOSURE)

A B C D

: \ I I : 1 1 j j

I .a,..

0.01 0.1 0.25 0.5 1.0 2.0 10.0

b SPATIAL FREQUENCY(wmm)

Fig. 8. Image processing conditions for Fig. 7. The frequency enhancement rank was controlled at a relatively low level of 3.0 at all spatial frequency areas (b). However, gradation was linear, in which the inclination of the straight line, i.e., the gamma value, was large, 1.4 in GA, centered around a density of 1.2 (a).

Table III. Gingival cancer

Diagnostic feature Gradational Spatial frequency enhancement enhancement

Border of lesion Bone destruction Floating teeth Bone trabeculae around

lesion Fine bony abnormality Gross bony abnormality

++ ++ ++ +++ ++ +++ ++ ++

+ + + +

Scale: (+++) = Optimal visualization; (++) = Adequate; (+) = Poor but diagnostic; (0) = Unacceptably poor.

Table IV. Osteomyelitis

Gradational Spatial frequency Diagnostic feature enhancement enhancement

Border of lesion ++ ++ Increased radiopacity ++ ++ Alveolar crest + +++ Extension of lesion + + Bone trabeculae around + ++

lesion

Scale: (+++) = Optimal visualization; (++) = Adequate; (+) = Poor but diagnostic; (0) = Unacceptably poor.

radiography using processes developed by the Fuji Company. Image processing in CPR was divided into gradational enhancement and frequency enhance- ment. Gradational enhancement produced differ- ences in the radiographic image density, whereas fre- quency enhancement controlled the sharpness of the images.

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Diagnostic imaging of diseases afecting mandible 1 I s

Fig. 9. CPR images of osteomyelitis in specific spatial frequency areas with the use of frequency enhance- ment.

Our results show that images given frequency en- hancement are superior to those given gradational enhancement with respect to the outline of the cyst, expansion of the cortical bone, and anatomic details of the alveolar crest and teeth. Moreover, the fre- quency-enhanced image illustrates more clearly the gross bony destruction in gingival cancer. On the other hand, it is very difficult to illustrate the rare- faction of bone trabeculae associated with fibrous dysplasia in images given frequency enhancement. The border of the lesion and the increase in radiopa- city in the case of sclerosing-type osteomyelitis were, however, as sharp as in the gradationally enhanced image.

GA1.4

GA 1.0

GAO.6

a” 1 .

INPUT SIGNAL (EXPOSURE)

Since the maximum spatial resolution in CPR is 2.0 to 2.5 cycle/mm, it is possible that the rarefaction of trabeculae was in the frequency area of 2 cycle/mm or higher, whereas the increased radiopacity of tra- beculae was in the area lower than 2 cycle/mm in the cases imaged. This suggests that frequency enhance- ment will not permit reproduction of the “ground glass” appearance, a radiologic feature found in tra- becular rarefaction, and that the density changes vi- sualized by gradational enhancement are a better in- dication of pattern changes in rarefaction.

t A B C D

CONCLUSION

1. Diagnostic spatial frequency areas for the man- dibular lesions studied were in the range of 0.25 to 1 .O cycle/mm.

0.01 0.1 0.25 0.5 1.0 2.0 10.0

b SPATIAL FREOUENCY(c/mm)

2. The diagnostic value of images increased when Fig. 10. Image processing conditions for Fig. 9. Linear frequency enhancement rank was reduced in the gradation (a). The frequency enhancement rank was con- lower spatial frequency areas (0.25 to 0.5 cycle/mm) stant at 5.0 for all frequencies (b).

116 Kashima et al.

and increased in the higher spatial frequency areas (1 .O to 2.0 cycle/mm).

3. Linear gradational enhancement allowed clearer demonstration of bony trabeculae.

4. Frequency-enhanced images clearly demon- strated the outlines of lesions, bone destruction, and the trabecular pattern of the bone, but were not ad- equate for outlining the rarefaction of trabeculae in fibrous dysplasia.

5. Gradationally enhanced images were useful for detecting density changes in mandibular lesions.

REFERENCES

1. Kato H, Ishida M, Akimoto T. Photographic image simulation system for pictorial evaluation. Tokyo Symposium ‘77 on Photo and Electra-imaging, extended abstracts of papers. So- ciety of Photographic Scientists and Engineers (SPIE) 1971;19:1,7.

ORAL SURG ORAL MED ORAL PATHOL July 1990

Sonoda M, Takano M, Miyahara J, Kato H. Computed radi- ography utilizing scanning laser-stimulated luminescence. Radiology 1983;148:833-8. Kashima I, Kanno M, Higashi T, Takano M. Computed pan- oramic tomography with scanning laser-stimulated lumines- cence. ORAL SURG ORAL MED ORAL PATHOL 1985;60:448-53. Kashima I, Kanno M, Oguro T, et al. Bone trabecular pattern analysis in Down syndrome with the use of computed pan- oramic tomography with a laser scan system: quantitative analysis with the power spectrum method. ORAL SURG ORAL MED ORAL PATHOL 1988;65:366-70.

Reprint requests to: Dr. Isamu Kashima Professor and Head Department of Oral Radiology Kanagawa Dental College 82, Inaoka-cho, Yokosuka Kanagawa Japan