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THE

AMERICAN

OF

ROENTGENOLOGY RADIUM NUCLEAR

VOL.

JOURNAL

THERAPY AND MEDICINE ‘975

JULY,

I4

XEROTOMOGRAPHY TRACHEOBRONCHIAL By

OF

sions in the more radiolucent hilar regions (Fig. 3, A and B). This obviates the need for multiple exposures at varying techniques or specially designed and engineered filters as with film tomography to visualize these structures. Also, oblique projections can be obtained readily without additional techniques or filters. The visual enhancement of interfaces between different densities (edge enhancement) is an inherent property of xerography and of great value in detection of masses.”5’6 The quality of the xerotomograms in several cases was such that anticipated special studies such as bronchoscopy and bronchography were not performed (Fig. , A and B). In an attempt to substantiate our impression that xerotomography produces better images than film tomography of the trachea and bronchi, we investigated and compared the physical aspects of both modalities.

MATERIAL

Qualitatively, xerotomographic images appear superior to those on film tomograms (Fig. , A and B). The wide latitude of xerography permits visualization on a single image of the trachea and its bifurcation within the dense mediastinum, as well as the main bronchi and segmental ubdivithe Department

THE TREE*

TEXAS

PPLICATION of the xerographic process to tomography is a valuable aid in the evaluation of the tracheobronchial tree. Our interest in this combination of modalities results from the clear demonstration of stenosis of the trachea on a single oblique tomographic view using xerography (Fig. i). Prior conventional views of the chest and linear film tomograms of the trachea in this patient failed to reveal the suspected narrowing. This experience prompted utilization of the xerotomographic technique in selected patients with disorders of the tracheobronchial tree.

From

3

THOMAS S. HARLE, M.D.,t JAMES M. HEVEZI, PH.D., LEE F. ROGERS, M.D., JOHN E. MARTIN, M.D.,II and BAO-SHAN JING, M.D.II HOUSTON,

*

No.

of Radiology,

Hermann

Hospital,

The

University

t

Professor of Radiology. Assistant Professor of Radiology. § Associate Professor of Radiology. II Clinical Associate in Radiology.

353

of Texas

Medical

School

at Houston,

Houston,

Texas.

Harle,

354

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-

--

Hevezi, -

Rogers,

Martin

and

Jing

JULY,

‘975

-

I.

i. A 33 year old male treated months previously for severe chest injury following an automobile accident. Tracheal stenosis developed at the site of endotracheal cuff pressure.

FIG.

PHYSICAL

ASPECTS

Tomography may be considered as a recording of 2 types of information. Object details, which lie in the plane about which the x-ray tube-recording system move (fulcrum plane), are imaged as if only that plane, albeit of finite thickness, was radiographed. Superimposed on this are structures attributable to object details above and below the fulcrum plane which, owing to the particular motion during recording, are imaged as blurred structures. This blurring increases the farther the object details are from the fulcrum. The undesirable blurred details are low spatial frequency information which reduces contrast in the fulcrum plane. Previously, attempts have been made to remove the motion blur by image processing after the tomograms

I A 37 year i male with proved d carcinoma of the right lung. (1) Xerotomogram at midline of chest demonstrates tumor extending from the right main bronchus and hilar region into the carinal area and lower trachea. (Xerotomographic images are reversed as to right and left compared to roentgenograms.) (B) Linear film tomogram at the same level does not demonstrate this mass as clearly.

FIG.

.

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VOL.

124,

No.

3

Xerotomography

of the

Tracheobronchial

Tree

355

have been produced.2 These methods involve a two-step process and have not come into general use. A recording system which selectively reduces low spatial frequency information and enhances the higher frequencies is desirable. These features are present inherently in the xerographic process. Figure 5 illustrates in a qualitative fashion the modulation transfer function for a screen-film system (a), and xeroradiography (b).’ The curve for xerographic recording indicates the selective attenuation of low spatial frequencies in the image which is a desired feature for tomography. Resolution for xeroradiographv lies between that of industrial film and film-screen systems. Subjectively, this is adequate for tomography of the tracheobronchial tree. Other tomographic techniques may require greater resolution, but this must be determined for each area. Thickness of cut for film tomography and xerotomographv at a fixed tomographic angle (4Q0) was determined using a lead bar line test pattern. The fulcrum was moved in millimeter increments above and below the level of the test pattern and the resulting images analyzed for amount of blurring at each frequency. The results are shown in Figure 6, where the last discernible group of bars is plotted as a function of displacement from the fulcrum. Thickness of cut cannot be defined precisely but at an arbitrary ordinate value, the full width of the curve indicates thickness of cut. At all frequencies, the xerographic thickness of cut exceeds the film-screen value. Xerography is less sensitive to x-rays than film-screen combinations. Thus more radiation must be used to produce satisfactory images. Patient exposures were measured with calibrated thermolu minescent dosimeters placed on the surface of the patient in the middle of the field. For the

3. (4) A year old male with carcinoma of the left main bronchus. Note the narrowing of the left main bronchus. The segmental bronchi are clearly visualized on the right as well as the main bronchi. (B) A 63 year old woman with repeated episodes of right middle lobe pneumonia. Oblique xerotomogram demonstrated not only the main bronchus, but also the lobar divisions. i’he right middle lobe bronchus is well visualized with no evidence of narrowing.

FIG.

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356

Harle,

Hevezi,

Rogers,

Martin

and

Jing

JULY,

1975

0 4. (ii) A 65 year old male with history of right pneumonectomy 6 years previously. ness of breath. The xerotomogram demonstrates a mass almost occluding the trachea. had been scheduled for the next day wascancelled and radiation therapy instituted. with left lower lobe consolidation. Xerotomography demonstrates mass occluding bronchus. Bronchography had been scheduled but was cancelled due to demonstration Biopsy at bronchoscopy revealed squamous cell carcinoma.

FIG.

average film tomogram technique employed (62 kVp., 25 mAs.), the exposure measured 470 mr. In contrast, the average xerotomographic technique (120 kVp., 200 mAs.) resulted in an exposure of 7.5 r. On a per exposure basis, the exposure for xerotomography is approximately i5 times that of the film-screen system employed at this institution. However, due to the wide radiographic latitude of xerography, a single xerotomogram may be sufficient to arrive at a diagnosis, whereas many film tomograms might be required. While we feel that xerotomographic images are preferable to those of film tomography, the pa-

He developed shortBronchoscopy which (B) A73 year old male the left lower lobe of this occlusion.

tient exposure is too high to justify the use of xerotomography in this area routinely. The quality and potential of this technique warrant attempts to reduce exposure levels. As a step in this direction, we have increased the sensitivity of the xerographic process by installation of a high atomic number gas within the xerographic cassette.4 This technique nearly doubles the sensitivity, thereby reducing the patient exposure by one-half with only slight loss of resolution. SUMMARY

The

inherent

features

in xerography

of

VOL.

124,

No.

Xerotomography

3

of the

Tracheobronchial

Tree

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THICKNESS wide latitude, edge enhancement, and reduction of the off fulcrum plane blur make it a desirable recording modality to use in conjunction with tomography. Xerotomographic images appear superior to those of film tomograms. The principal obstacle to routine use of xerotomography in this area is the high patient exposure. Attempts to increase the sensitivity of the xerographic system thereby reducing patient exposure, are being investigated.

357 OF CUT COMPARISON

3.0W

Xero/omogrcms E E

2.0

Q.

U)

w

z

-J

w -J

I.O

U)

Thomas S. Harle, M.D. Department of Radiology

Hermann

Hospital

The

University of Texas Medical School at Houston 1203 Ross Sterling Avenues Houston, Texas 77025

I

-5

-4

I

-3

-2

I

-I

DISPLACEMENT MTF

I

0

I

I

2

3

4

FROM FULCRUM (mm)

COMPARISON

Fic.

FILM

SCREEN

6. Thickness of cut comparison between xerotomograms and film tomograms. Tomograms were made using 40#{176}linear cuts of a lead bar pattern; data are plotted as the last visible line pattern group versus the displacement of the lead pattern from the fulcrum plane.

SYSTEM

a

REFERENCE5 i.

C. W.,

Bmtossi,

diography Li.

of lung.

and MARTIN, Radiology,

J. E. 1973,

Xerora-

107,

217-

22!.

I-

2. x a.

1970,

4

3.

C, 0 0 4

XERORADIOGRAPHIC SYSTEM

b

SPATIAL

FREQUENCY (Ip/mm)

Fic.

5. Modulation transfer function (MTF) comparison between (a) screen-film and (b) xerographic recording media.3 Note the selective attenuation of low spatial frequency information afforded by the xerographic recording process.

P.,

EDHOLM,

in

C)

linear JO,

and QUILING, tomography.

L. Elimination 4cta radiol.

of blur (Diag.),

44!.

W. D. Radiographic Image Analysis Through Application of the Radiographic Modulation Transfer Function and System Phase Response. In: Quantitative Imagery in the BioMedical Sciences. Presented at Seminar-inDepth, Society of Photo-optical Instrumentation Engineers, Houston, Texas, May 10, 1971. 4. HEVEZI, J. M., and HARLE, T. S. Intensifying “screen” for xeroradiography? Presented at Radiological Society of North America, Chicago, Illinois, November 30, 1973. . Ruzci, F. F., KAUFMAN, L., SHAPIRO, G., PEREZ, J., and GROSS!, C. E. Xeromammography and film mammography: comparative study. Radiology, 1965, 85, 260-269. 6. WOLFE, J. N. Xeroradiography: image content and comparison with film roentgenograms. AM. J. ROENTGENOL., RAD. THERAPY & NuCLEAR MED., 1973, 117, 69o-695. FENDER,

5

The american journal of roentgenology radium therapy and nuclear medicine.

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