Description of a new Cephalostat and its Performance Masao Iikubo, D. D. S. *), Sven Korsell and Karl-Ake Omnell, D. D. S., Ph. D.
Oral Roentgendiagnostic Department University of Lund, School of Dentistry, Malmo, Sweden. Introduction
Studies of the growth of the facial skeleton and evaluation of orthodontic treatment are some of the most common applications of roentgen cephalometry. Such studies require repeated examination of the patient. This in turn requires good reproduction of the relative positions of the focus of the roentgen tube, the subject and the plane of the film. The roentgen tube and the plane of the film can be fixed to one another. The problem is however, to position the subject in a reproducible relation to the roentgen tube and the plane of the film. MOORREES & KEAN (1958) showed that the head can be positioned unsupported with a remarkably good reproducibility, as judged from two observations at an interval of one week. They roentgenogaphed the subjects sitting at ease looking at themselves in a mirror. However, since BROADBENT'S (1931) and HOFRATH'S (1931) introduction of cephalostats as an aid for obtaining standard lateral head roentgenograms, roentgen cephalometric analyses have been based almost exclusively on roentgenograms obtained with the subject positioned in a cephalostat. Examples of different cephalostat constructions have been published by KROGMAN & SASSOUNI (1957). Most cephalostats are technically complicated, a fact which makes them difficult to handle for auxiliary personnel. The aim of our investigation was to construct a cephalostat which would be simple to operate for assisting personnel. This paper describes a new cephalostat and its performance.
possible for dental assistants and roentgen technicians to handle the apparatus with a satisfying precision. 2. The distance between the median plane and the film should be adjustable between well defined positions. The magnification should be marked on the roentgen film to indicate the distance between the median plane and the film. 3. The patient's head should be fixed by ear rods and a forehead and/or neck support. The ear rods and other supports of the head should be as radiolucent as possible. The ear rods should be of such a shape as to enable good fixation of the head of an adult or child and allow practically no lateral movement of the head. 4. It should not be necessary for the patient to change his position between the taking of lateral and of postero-anterior roentgenograms. Instead the cassette holder should be rotatable 90°.
5. The cassette holder should have an opening for receiving an image intensifier. 6. The cassette holder should be rotatable in
the plane of the cassette. Its axis of rotation should be eccentric to the middle of the cassette holder, so that the same size of the film may be used for both lateral and posteroanterior roentgenograms, without it being necessary to move the cassette holder in the vertical plane between two exposures. 7. The cephalostat should be rotatable in the horizontal plane in steps of 15° to enable oblique lateral views.
Description of the cephalostat
8. An aluminium wedge used to bring out the
Fundamental requirements
soft tissues in lateral views should be shaped in such a way that it can be placed near the focus instead of near the film. This would
The following requirements were set up. 1. The cephalostat should be simple in design
and mounted in such a way as to make it easy to work around the patient. It should be Dentomaxillofac. Radiol. 4:25-29 (1975)
'J Present address: Nihon University, School of Dentistry, 101 1-8 Surugadai, Chiyoda-ku, Tokyo.
25
simplify positioning of the patient in the cephalostat. Design
Fig. 1 gives schematic drawing of the cephalostat. The cephalostat is suspended from the ceiling by a strong rod (A, Fig. 1) which is eccentric to three round metal plates (B, C, 0, Fig. I), which are the main components of the cephalostat. The suspension rod is fastened to the upper metal plate (B), on which are mounted also the controls (E and F, Fig. 1) of the cephalostat and the attachement (G) for the cassette holder (H). The lower metal plate (0) has a groove with movable attachements for the ear rods (I), which are moved on rotation of the metal plate (C). On the underneath side of (0) a forehead and neck support (K) can be attached. The ear rods, which are made of plexiglass, can be moved symmetrically by the lever (E) and locked in position by lever (F). The ear plugs (L) (ad modum Seipel) are concentric and their longitudinal axes are directed somewhat forwards and upwards in order to fit the natural course of the external auditory ducts. The largest possible distance between the medial parts of the ear plugs is 180 mm. The forehead and neck supports are of identical shape and made of plexiglass. They are detachable and can be moved vertically and adjusted in postero-anterior direction along a slide (M) which is fastened to the lower metal plate. The forehead and neck supports are locked by two set-screws (N). They have two metal ball-bearings (0) countersunk at a distance of 30 mm apart. The balls serve as calibration object for checking the magnification in the roentgenogram. The lower metal plate (0) can be rotated about an axis running through the centre of the metal plates. The rotation is made possible by withdrawal of a springloaded pin (P). At every 15th degree, the pin passes a hole in the plate in which it can be inserted. The attachment (G) for the cassette holder can be rotated 90 0 and fixed in position for lateral or postero-anterior roentgenograms by a ball latch (R). In these positions the attachment can be moved towards or from the cephalostat and occupy positions allowing the 26
K
L
H
Fig. 1: Diagrammatic representation of the cephalostat. A, Rod suspending the cephalostat from the ceiling B, C, D, Three round metal plates constituting the main components of the cephalostat. E, F, Controls. G, Attachement for the cassette holder. H, Cassette holder. LEar rods. K, Forehead and neck supports. L, Ear plugs. M, Slide for the forehead and neck supports. N, Set-screws for locking the forehead and neck supports. 0, Ball-bearings serving as calibration object for checking the magnification in the roentgenogram. P, Spring-loaded pin.
f f f
f
,, f
,..---, , f
, L_-
f
i
l
, J
support is then fitted, after which the cassette holder is placed in its innermost position near the patient's face. Usually only the forehead support is used. With the cassette holder fully drawn out or pushed in, the distance between the image of the metal balls (0) in lateral views will be33.8 and 32.5 mm, respectively. Provided that two stationary roentgen tubes are used, the only change of adjustment necessary between the taking of a lateral film and a postero-anterior film is to swing the cassette holder through 90°. Performance of the cephalostat Material and Method
H
L
film to be placed with defined endpositions 100 to 150 mm from the middle of the cephalostat. The cassette holder (H) is provided with a Lysholm grid and the back side of the holder has a round hole (130 mm in diam.) to which an image intensifier can be adapted. To obtain good reproduction of the soft tissue profile an aluminium wedge is used, which is placed at the roentgen tube in front of a light diaphragm. The aluminium wedge can be adjusted and rotated in a vertical plane perpendicular to the roentgen beam. When a lateral view of the skull is to be taken, the patient is placed in a chair fitted with castors and adjustable in both the horizontal and the vertical direction. On adjustment of the patient the cassette holder is in its extreme position, 150 mm from the middle of the cephalostat. The ear rods are likewise in their extreme outer positions. The forehead and neck supports are removed. The ear plugs are inserted with the aid of the adjustment lever and locked in desired position with the other lever when the head is fixed. The forehead and/or neck
The precision *) with which the cephalostat worked was tested on 26 lateral roentgenograms of the skull of 13 patients aged 5-24 years. All of the positionings and exposures were made by auxiliary personnel. Two films were taken of each patient. After the first exposure the patient was removed from the cephalostat. After a while another assistant was instructed to take another roentgenogram of the patient. Each roentgenogram was studied in transmitted light of variable intensity. The roentgenograms were covered with transparent paper, on which the following reference points (Fig. 2) defined according to KROGMAN & SASSOUNI (1957) and SOLOW (1966) were traced: Basion. The most postero-inferior point ba on the clivus. go Gonion. The lowest point of the angle of the mandible to which a tangent can be drawn from the gnathion. n Nasion. The most anterior point of the fran to-nasal suture. s Sella. The centre of the sella turcica. The upper limit of the sella turcica is defined as the line joining the tuberculum and dorsum sellae. ss Subspinale. The most posterior point on the anterior contour of the lower alveolar arch. Between the reference points lines were drawn and the following four angles were measured with a protractor, graduated in OJ Precision is defined as a quality associated with a class of observations and referring to the closeness of replicated or repeated observations around the mean. (Hallert, 1964).
27
profile without itself causing any distinct image. Some results of the analysis of variance are given in Table 1 where Sf denotes standard deviations between roentgenograms within patients and 5,. denotes standard deviations between trancings within patients. The analysis of - variance did not reveal any differences between roentgenograms within patients.
-> Reference point and angles used in determining the performance of the cephalostat.
Fig. 2 :
Table 1 : Some results of the analysis of variance. Sf denotes standard deviations between tracings within patients. None of the angles measured showed any differences between roentgenograms within patients.
Angle
Sf
St.
s-n-ss s-n-sm
0 0 .3 0.3 0
0 .7 0 .6 1.1 1.0
s-ri-go
s-n-ba
Fig . 3 : Lateral roentgenogram of a 12 year old patient taken with the cephalostat described in the present paper. The aluminium wedge, placed near the focus, contributes to a good image of the soft tissue profile.
tenths of degrees: s-n-ss, s-n-sm, s-n-go, s-n-ba, The two images of each patient were each measured twice at an interval of about one week between each measurement. The numerical material was afterwards treated with analysis of variance (nested classification). Results and Discussion
Fig. 3 gives a reproduction of a lateral roentgenogram of the skull and facial skeleton of a 12-year old patient. It is obvious that the aluminium wedge, placed near the focus, contributes to a good image of the soft tissue 28
It is clear from Table 1 that the variations produced by positioning in the cephalostat and thereby of the function of the cephalostat were insignificant, compared with those found on repeated measurement of the same roentgenogram. It is therefore of interest to compare these variations with corresponding variations reported by earlier investigators. Perusal of the literature revealed that the variation found in the present investigation was of the same order as those reported by BJORK (1947), BROADWAY, HEALY & POYTON (1962), BROWN (1965), SOLOW (1966) and BENETT & SMALE5 (1969) . The cephalostat described thus proved to be satisfactory for positioning of the head for lateral views of the skull. References: 1. Bennett, D . T. and Smales, F. C.: Accuracy of angular measurements obtained from radiographic cephalometric analysis , J Dent Res 48:595, 1969 . 2. Bjork, A .: The face in profile, Sven Tandlak Tidskr 40: 5 B, 1947 .
3. Broadbent , H . : A new X-ray technique and it s appl ication to orthodontia, Angle Orthod 1 : 45 , 1931. 4. Broadway, E. 5 .. Heal y, M. J. R. and Pe yton, H . G. : The accuracy of tracings from cepha lo me tric lateral skull rad iographs, Transactions of the Brit ish Society for the study of orthodontics. 1962, pp 9-14 . 5. Br own , T . : C ran iofacial variations in a ce n t ra l Australian tribe, Thesi s . Adelaide . Libraries Board of South Au stralia 1965. 6. Hallett. B. : Glo ssa ry of some terms and expressions used in the theory of errors of photogrammetry . International Society fo r Photog rammetr-y, Commission VI, 1964 .
7. Hofrath , H . : Die Bedeutung der Rontgenfern- und Ab standsau fnahme fur die Diagnostik der Kieferanomalien, Fortschr . d . Orthod . 1 :23 2, 1931.
8. Krogman, N. M. and Sassouni, V.: Syllabus in roentgenographic cephalometry, Philadelphia Center for Research in Child growth, 1957. 9. Moorrees, C. F. A. and Kean, M. R.: Natural head position, a basic consideration in
the
interpretation of
cephalometric radiographs, Am J. Phys Anthropol 16: 213, 1958. 10. Seipel, C. M.: Ortodontisk bettregistrering, Sven Tandlak Tidskr. Vol. 39:465 (1946). 11. Solow,
B.:
The
pattern
of
craniofacial associations,
Acta Odontol Scand. Vol. 24 Suppl. 46, 1966.
Acknowledgement The authors are indebted to Ingemar Nilsson, EM., Department of Statistics, University of Lund, for help with the statistical analysis. Prof. K.-A. Omnell School of Dentistry Carl Gustavs vag 34 S-214 21 Malmo/Sweden
Summary:
A description is given of a new cephalostat, simple in design and easy to handle also for auxiliary personnel. The performance of the cephalostat was investigated. When lateral roentgenograms were taken of the head the variations produced by positioning in the cephalostat were insignificant compared with those found on repeated measurement of the same roentgenogram.
29
Oral Roentgendiagnostic Department University of Lund, School of Dentistry, Malmo, Sweden. Introduction
Studies of the growth of the facial skeleton and evaluation of orthodontic treatment are some of the most common applications of roentgen cephalometry. Such studies require repeated examination of the patient. This in turn requires good reproduction of the relative positions of the focus of the roentgen tube, the subject and the plane of the film. The roentgen tube and the plane of the film can be fixed to one another. The problem is however, to position the subject in a reproducible relation to the roentgen tube and the plane of the film. MOORREES & KEAN (1958) showed that the head can be positioned unsupported with a remarkably good reproducibility, as judged from two observations at an interval of one week. They roentgenogaphed the subjects sitting at ease looking at themselves in a mirror. However, since BROADBENT'S (1931) and HOFRATH'S (1931) introduction of cephalostats as an aid for obtaining standard lateral head roentgenograms, roentgen cephalometric analyses have been based almost exclusively on roentgenograms obtained with the subject positioned in a cephalostat. Examples of different cephalostat constructions have been published by KROGMAN & SASSOUNI (1957). Most cephalostats are technically complicated, a fact which makes them difficult to handle for auxiliary personnel. The aim of our investigation was to construct a cephalostat which would be simple to operate for assisting personnel. This paper describes a new cephalostat and its performance.
possible for dental assistants and roentgen technicians to handle the apparatus with a satisfying precision. 2. The distance between the median plane and the film should be adjustable between well defined positions. The magnification should be marked on the roentgen film to indicate the distance between the median plane and the film. 3. The patient's head should be fixed by ear rods and a forehead and/or neck support. The ear rods and other supports of the head should be as radiolucent as possible. The ear rods should be of such a shape as to enable good fixation of the head of an adult or child and allow practically no lateral movement of the head. 4. It should not be necessary for the patient to change his position between the taking of lateral and of postero-anterior roentgenograms. Instead the cassette holder should be rotatable 90°.
5. The cassette holder should have an opening for receiving an image intensifier. 6. The cassette holder should be rotatable in
the plane of the cassette. Its axis of rotation should be eccentric to the middle of the cassette holder, so that the same size of the film may be used for both lateral and posteroanterior roentgenograms, without it being necessary to move the cassette holder in the vertical plane between two exposures. 7. The cephalostat should be rotatable in the horizontal plane in steps of 15° to enable oblique lateral views.
Description of the cephalostat
8. An aluminium wedge used to bring out the
Fundamental requirements
soft tissues in lateral views should be shaped in such a way that it can be placed near the focus instead of near the film. This would
The following requirements were set up. 1. The cephalostat should be simple in design
and mounted in such a way as to make it easy to work around the patient. It should be Dentomaxillofac. Radiol. 4:25-29 (1975)
'J Present address: Nihon University, School of Dentistry, 101 1-8 Surugadai, Chiyoda-ku, Tokyo.
25
simplify positioning of the patient in the cephalostat. Design
Fig. 1 gives schematic drawing of the cephalostat. The cephalostat is suspended from the ceiling by a strong rod (A, Fig. 1) which is eccentric to three round metal plates (B, C, 0, Fig. I), which are the main components of the cephalostat. The suspension rod is fastened to the upper metal plate (B), on which are mounted also the controls (E and F, Fig. 1) of the cephalostat and the attachement (G) for the cassette holder (H). The lower metal plate (0) has a groove with movable attachements for the ear rods (I), which are moved on rotation of the metal plate (C). On the underneath side of (0) a forehead and neck support (K) can be attached. The ear rods, which are made of plexiglass, can be moved symmetrically by the lever (E) and locked in position by lever (F). The ear plugs (L) (ad modum Seipel) are concentric and their longitudinal axes are directed somewhat forwards and upwards in order to fit the natural course of the external auditory ducts. The largest possible distance between the medial parts of the ear plugs is 180 mm. The forehead and neck supports are of identical shape and made of plexiglass. They are detachable and can be moved vertically and adjusted in postero-anterior direction along a slide (M) which is fastened to the lower metal plate. The forehead and neck supports are locked by two set-screws (N). They have two metal ball-bearings (0) countersunk at a distance of 30 mm apart. The balls serve as calibration object for checking the magnification in the roentgenogram. The lower metal plate (0) can be rotated about an axis running through the centre of the metal plates. The rotation is made possible by withdrawal of a springloaded pin (P). At every 15th degree, the pin passes a hole in the plate in which it can be inserted. The attachment (G) for the cassette holder can be rotated 90 0 and fixed in position for lateral or postero-anterior roentgenograms by a ball latch (R). In these positions the attachment can be moved towards or from the cephalostat and occupy positions allowing the 26
K
L
H
Fig. 1: Diagrammatic representation of the cephalostat. A, Rod suspending the cephalostat from the ceiling B, C, D, Three round metal plates constituting the main components of the cephalostat. E, F, Controls. G, Attachement for the cassette holder. H, Cassette holder. LEar rods. K, Forehead and neck supports. L, Ear plugs. M, Slide for the forehead and neck supports. N, Set-screws for locking the forehead and neck supports. 0, Ball-bearings serving as calibration object for checking the magnification in the roentgenogram. P, Spring-loaded pin.
f f f
f
,, f
,..---, , f
, L_-
f
i
l
, J
support is then fitted, after which the cassette holder is placed in its innermost position near the patient's face. Usually only the forehead support is used. With the cassette holder fully drawn out or pushed in, the distance between the image of the metal balls (0) in lateral views will be33.8 and 32.5 mm, respectively. Provided that two stationary roentgen tubes are used, the only change of adjustment necessary between the taking of a lateral film and a postero-anterior film is to swing the cassette holder through 90°. Performance of the cephalostat Material and Method
H
L
film to be placed with defined endpositions 100 to 150 mm from the middle of the cephalostat. The cassette holder (H) is provided with a Lysholm grid and the back side of the holder has a round hole (130 mm in diam.) to which an image intensifier can be adapted. To obtain good reproduction of the soft tissue profile an aluminium wedge is used, which is placed at the roentgen tube in front of a light diaphragm. The aluminium wedge can be adjusted and rotated in a vertical plane perpendicular to the roentgen beam. When a lateral view of the skull is to be taken, the patient is placed in a chair fitted with castors and adjustable in both the horizontal and the vertical direction. On adjustment of the patient the cassette holder is in its extreme position, 150 mm from the middle of the cephalostat. The ear rods are likewise in their extreme outer positions. The forehead and neck supports are removed. The ear plugs are inserted with the aid of the adjustment lever and locked in desired position with the other lever when the head is fixed. The forehead and/or neck
The precision *) with which the cephalostat worked was tested on 26 lateral roentgenograms of the skull of 13 patients aged 5-24 years. All of the positionings and exposures were made by auxiliary personnel. Two films were taken of each patient. After the first exposure the patient was removed from the cephalostat. After a while another assistant was instructed to take another roentgenogram of the patient. Each roentgenogram was studied in transmitted light of variable intensity. The roentgenograms were covered with transparent paper, on which the following reference points (Fig. 2) defined according to KROGMAN & SASSOUNI (1957) and SOLOW (1966) were traced: Basion. The most postero-inferior point ba on the clivus. go Gonion. The lowest point of the angle of the mandible to which a tangent can be drawn from the gnathion. n Nasion. The most anterior point of the fran to-nasal suture. s Sella. The centre of the sella turcica. The upper limit of the sella turcica is defined as the line joining the tuberculum and dorsum sellae. ss Subspinale. The most posterior point on the anterior contour of the lower alveolar arch. Between the reference points lines were drawn and the following four angles were measured with a protractor, graduated in OJ Precision is defined as a quality associated with a class of observations and referring to the closeness of replicated or repeated observations around the mean. (Hallert, 1964).
27
profile without itself causing any distinct image. Some results of the analysis of variance are given in Table 1 where Sf denotes standard deviations between roentgenograms within patients and 5,. denotes standard deviations between trancings within patients. The analysis of - variance did not reveal any differences between roentgenograms within patients.
-> Reference point and angles used in determining the performance of the cephalostat.
Fig. 2 :
Table 1 : Some results of the analysis of variance. Sf denotes standard deviations between tracings within patients. None of the angles measured showed any differences between roentgenograms within patients.
Angle
Sf
St.
s-n-ss s-n-sm
0 0 .3 0.3 0
0 .7 0 .6 1.1 1.0
s-ri-go
s-n-ba
Fig . 3 : Lateral roentgenogram of a 12 year old patient taken with the cephalostat described in the present paper. The aluminium wedge, placed near the focus, contributes to a good image of the soft tissue profile.
tenths of degrees: s-n-ss, s-n-sm, s-n-go, s-n-ba, The two images of each patient were each measured twice at an interval of about one week between each measurement. The numerical material was afterwards treated with analysis of variance (nested classification). Results and Discussion
Fig. 3 gives a reproduction of a lateral roentgenogram of the skull and facial skeleton of a 12-year old patient. It is obvious that the aluminium wedge, placed near the focus, contributes to a good image of the soft tissue 28
It is clear from Table 1 that the variations produced by positioning in the cephalostat and thereby of the function of the cephalostat were insignificant, compared with those found on repeated measurement of the same roentgenogram. It is therefore of interest to compare these variations with corresponding variations reported by earlier investigators. Perusal of the literature revealed that the variation found in the present investigation was of the same order as those reported by BJORK (1947), BROADWAY, HEALY & POYTON (1962), BROWN (1965), SOLOW (1966) and BENETT & SMALE5 (1969) . The cephalostat described thus proved to be satisfactory for positioning of the head for lateral views of the skull. References: 1. Bennett, D . T. and Smales, F. C.: Accuracy of angular measurements obtained from radiographic cephalometric analysis , J Dent Res 48:595, 1969 . 2. Bjork, A .: The face in profile, Sven Tandlak Tidskr 40: 5 B, 1947 .
3. Broadbent , H . : A new X-ray technique and it s appl ication to orthodontia, Angle Orthod 1 : 45 , 1931. 4. Broadway, E. 5 .. Heal y, M. J. R. and Pe yton, H . G. : The accuracy of tracings from cepha lo me tric lateral skull rad iographs, Transactions of the Brit ish Society for the study of orthodontics. 1962, pp 9-14 . 5. Br own , T . : C ran iofacial variations in a ce n t ra l Australian tribe, Thesi s . Adelaide . Libraries Board of South Au stralia 1965. 6. Hallett. B. : Glo ssa ry of some terms and expressions used in the theory of errors of photogrammetry . International Society fo r Photog rammetr-y, Commission VI, 1964 .
7. Hofrath , H . : Die Bedeutung der Rontgenfern- und Ab standsau fnahme fur die Diagnostik der Kieferanomalien, Fortschr . d . Orthod . 1 :23 2, 1931.
8. Krogman, N. M. and Sassouni, V.: Syllabus in roentgenographic cephalometry, Philadelphia Center for Research in Child growth, 1957. 9. Moorrees, C. F. A. and Kean, M. R.: Natural head position, a basic consideration in
the
interpretation of
cephalometric radiographs, Am J. Phys Anthropol 16: 213, 1958. 10. Seipel, C. M.: Ortodontisk bettregistrering, Sven Tandlak Tidskr. Vol. 39:465 (1946). 11. Solow,
B.:
The
pattern
of
craniofacial associations,
Acta Odontol Scand. Vol. 24 Suppl. 46, 1966.
Acknowledgement The authors are indebted to Ingemar Nilsson, EM., Department of Statistics, University of Lund, for help with the statistical analysis. Prof. K.-A. Omnell School of Dentistry Carl Gustavs vag 34 S-214 21 Malmo/Sweden
Summary:
A description is given of a new cephalostat, simple in design and easy to handle also for auxiliary personnel. The performance of the cephalostat was investigated. When lateral roentgenograms were taken of the head the variations produced by positioning in the cephalostat were insignificant compared with those found on repeated measurement of the same roentgenogram.
29
