Radiolucent head support

A head support for a patient support table having a skull securing clamp that is mounted to a non-circular support bar for selective attachment to the side rails of the patient support table. The skull clamp includes a non-circular support aperture for receiving the non-circular support bar. The structural components of the head support are made from radiolucent material and the support bar includes mounting posts at its first and second ends so that arms for mounting the support bar to the side rails may be located out of the path of the x-rays through the patient's head. The non-circular shape of the support aperture and the support bar prevent inadvertent rotation of the radiolucent skull securing clamp with respect to the radiolucent support bar. The location of the mounting posts on the support arms and the utilization of the radiolucent material results in fewer artifacts in the developed x-ray picture.

FIELD OF THE INVENTION 
This invention relates to radiological equipment and, more particularly, 
radiological equipment used in neurological radiography. 
BACKGROUND OF THE INVENTION 
Supports for securing the head of a patient for surgical or radiological 
procedures are known in the art. The supports are typically adjustable so 
the head of the patient may be secured in different positions for 
different radiological views or to facilitate access to a patient's head 
during a surgical procedure. Such head supports typically include a 
support beam adapted to be mounted outward from one end of a patient 
support table, a head clamp, and one or more intervening adjusting members 
for adjusting the height and orientation of the head clamp with respect to 
the table. Such head supports are disclosed in U.S. Pat. Nos. 4,545,572 
and 4,169,478 which are assigned to the assignee of the present 
application and commercialized by Ohio Medical Instrument Company, Inc. as 
the Mayfield.TM. Headrest. 
The components of such head supports have usually been fabricated from 
stainless steel or other metals. One problem with head supports comprised 
of metal components is that the metal is radiopaque to x-rays which 
produces "artifacts" in the x-rays taken when the headrest is interposed 
between the x-ray source and the x-ray film. These artifacts are created 
by the metal head support components blocking the path of the x-rays as 
they travel from the source to the film. The areas of the x-ray film that 
remain unexposed because the x-rays are blocked by the head support appear 
as artifacts in the developed x-ray picture. These artifacts diminish the 
usefulness of the developed x-ray picture because they obscure the image 
of a portion of the head that normally would be viewable, absent the 
obscuring head support component. 
The use of radiolucent materials which permit x-rays to pass through them 
have been used in known head supports to reduce artifacts. While the x-ray 
pictures produced by using these head supports have fewer artifacts, they 
present other problems to the radiologist. Specifically, most known head 
supports are mounted to one end of the patient support table at or near 
the center of the table's width with mounting rails. The mounting rails 
are made from radiopaque materials because the radiolucent materials are 
not sufficiently strong enough to rigidly hold the head support. While the 
radiolucent material of the head support components permits most of the 
x-rays to pass through, the mounting rails do block part of the x-rays 
which results in a smaller artifact but one which can obscure finer 
details in a developed x-ray picture. What is needed is a way of reducing 
the number of headrest components that are interposed between the x-ray 
source and the x-ray film. 
Another problem with previously radiolucent head supports is the difficulty 
of mating an adjustable head support made from a radiolucent material to 
another component made of radiolucent material so the two components do 
not slip relative to one another under the pressure exerted by the 
patient's head. Slippage occurs because the surfaces of the radiolucent 
material have lower coefficients of friction than those of the metal 
surfaces in previously known head supports. While circumferential collars 
and grooved surfaces have been previously used, they require machining and 
the incorporation of tightening devices such as threaded bolts and 
apertures. What is needed is a simple way to maintain a mating 
relationship between head support components made from radiolucent 
materials. 
SUMMARY OF THE INVENTION 
To solve the above identified problems, a head support built in accordance 
with the principles of the present invention includes an adjustable skull 
clamp and a non-circular support bar made of radiolucent material so the 
skull clamp may be non-rotatably mounted to the support bar. Preferably, a 
securing screw is provided to bias the skull clamp into the non-rotatable 
mounting relationship with the support bar. Most preferably, the support 
bar is a non-circular solid having cylindrical mounting posts at its first 
and second ends and the skull clamp includes a non-circular aperture for 
snugly receiving the support bar intermediate the mounting post. 
The head support built in accordance with the principles of the present 
invention may be mounted to the side rails of a patient support table to 
remove the table mounting rails from the path of the x-rays as they pass 
through the patient's head to the x-ray film. The novel non-circular shape 
of the support bar and the aperture in the skull clamp prevents rotational 
movement of the skull clamp with respect to the support bar. The 
cylindrical posts mounted at the first and second ends of the support bar 
permit pivotal movement of the support in conventional mounting members 
that attach the support bar to the side rails of the patient support 
table. The head support of the present invention provides secure 
engagement of the skull clamp with the support bar so the position of the 
patient's head does not change during the taking of an x-ray and the 
developed x-ray picture contains fewer artifacts since the cylindrical 
posts at the first and second ends permit the support bar to be mounted to 
the side rails of the table and not at the center of the table width. 
These and other novel aspects and advantages of the present invention shall 
be made apparent from the accompanying drawings and the description 
thereof.

DETAILED DESCRIPTION OF THE INVENTION 
A head support 10 built in accordance with the principles of the present 
invention is shown in FIG. 1. Head support 10 is mounted to a patient 
support table 12 at one end of the table in a manner to be discussed in 
more detail below. The head support 10 includes a skull clamp 14, an 
adjustable bracket 16, a mounting member 18, and a support bar 20. Support 
bar 20 is mounted to side rails 22 by mounting arms 24, 24 at each end. 
Most preferably, the major structural members of skull clamp 14, 
adjustable bracket 16, mounting member 18, and support bar 20 are made 
from a carbon composite material preferably comprised of polyethersulfone 
(PES) and carbon with the carbon component being 30% of the composite by 
weight. Such a material is available from ICI Advanced Materials of Exton, 
Pa. under the commercial name THERMOCOMP JC-1006 or from LNP Engineering 
Plastics, Inc. of Thorndale, Pa. under the commercial name STAT-KON 
JC-1006. Alternatively, the skull clamp 14 and adjustable bracket 16 may 
be made with the carbon composite material and the mounting member 18 and 
the support bar 20 may be made from a radiolucent plastic such as acetal. 
(Minor structural elements such as springs, pins or the like not directly 
in the path of the x-rays (FIG. 2) may be made of metal but it is 
desirable to eliminate the use of metal to the greatest extent possible.) 
In more detail, the head support 10 of FIG. 1 includes a U-shaped skull 
clamp 14 having a cradle 30 and a screw 32 mounted at opposite ends of the 
clamp 14. Screw 32 and cradle 30 cooperate to secure a patient's head in a 
fixed position in a conventionally known manner. Intermediate the ends of 
the U-shaped clamp 14 is a mounting collar 34 having V-grooves cut in the 
collar and also having a screw receiving aperture (not shown) concentric 
with the collar 34 for mounting the U-shaped clamp 14 to adjustable member 
16. 
Adjustable member 16 includes a pair of pivotable mounting arms 36a, 36b 
and a mounting post 38. At one end of mounting post 38 is a bore (not 
shown) through which an adjusting screw 39 is received. The adjusting 
screw 39 has a knob 40 mounted at one end so the adjusting screw 39 may be 
selectively tightened and loosened within the threaded aperture. Opposite 
the knob 40 is a mounting collar 42 having V-grooves that mate with the 
V-grooves of mounting collar 34 on skull clamp 14. By rotating knob 40 so 
the adjusting screw 39 is advanced through the aperture in post 38 and the 
aperture within mounting collar 34, the skull clamp 14 is fixedly mounted 
to the mounting post 38. The orientation of the skull clamp may be changed 
with respect to mounting post 38 by loosening the adjusting screw with the 
knob 40, rotating the mounting collar 34 with respect to mounting collar 
42 and then re-tightening the screw 39 to hold the mounting collars in 
engagement with one another. At its other end, mounting post 38 includes a 
mounting cylinder 44 having V-grooves at each end of the cylinder and a 
passageway through the cylinder for receiving a mounting bolt having a 
knob 45. 
Adjustment arms 36a, 36b have V-groove collars 50a, 50b at one end and 
mounting receptacles 52a, 52b at the other end. A mounting bolt having a 
knob 54 at one end passes through receptacle 52a of adjusting arm 36a and 
into receptacle 52b of adjusting arm 36b. The receptacle 52b is threaded 
so the adjusting bolt can be tightened by rotating knob 54. 
Mounting bracket 18 includes an aperture 58 at one end that is interposed 
and mated with the receptacles 52a, 52b of adjusting arms 36a, 36b, 
respectively. Placing the mounting bolt so it extends through the 
receptacles 52a, 52b and aperture 58 in mounting bracket 18 permits 
adjustable bracket 16 to be connected to the mounting bracket 18. Because 
adjustable bracket 16 may be rotated when knob 54 is turned to loosen the 
mounting bolt within receptable 52b, the vertical displacement of the head 
support 10 from the patient support table 12 may be selectively adjusted. 
The other end of mounting bracket 18 includes a support aperture 60 that 
is configured in the same non-circular shape as support bar 20 and sized 
to snugly receive the support bar 20 (FIG. 3). Mounting bracket 18 also 
includes a locking or set screw 61 having a knob 62 that may be used to 
selectively tighten the screw against a side of the support bar 20. 
Support bar 20 has a non-circular cross-section that mates with support 
aperture 60 of mounting bracket 18. Mounting bracket 18 may be moved 
intermediate the ends of support bar 20 to vary the horizontal 
displacement of the head support 10 within the width of the patient 
support table 12 and the selected horizontal position may be secured by 
screw 61. The mating of the non-circular support aperture 60 and the 
non-circular support bar 20 prevents rotational slippage between the 
mounting bracket 18 and the support bar 20 relative to one another while 
screw 61 set by knob 62 prevents horizontal displacement of the mounting 
bracket 18. In previously known head supports using radiolucent materials, 
securement of a cylindrical support bar within a cylindrical support 
aperture in a mounting bracket could not be maintained--even with a set 
screw. This is thought to arise from the low coefficient of friction of 
the two carbon composite surfaces. This rotational slippage problem is 
substantially reduced by the novel non-circular cross-section of the 
support bar 20 and support aperture 60 made according to the principles of 
the present invention. 
The mounting bracket 18 and support bar 20 of the present invention also 
permit horizontal adjustment of the head support along substantially the 
entire width of the support table 12 and removes the mounting arms 24 for 
mounting the support bar to the table 12 from the area underneath the 
skull clamp 14. The removal of the mounting arms 24 from this area results 
in fewer artifacts being produced by the head support components in the 
developed x-ray picture. 
Mounting posts 70a, 70b extend from ends 71a, 71b of support bar 20, 
respectively. The mounting posts 70a, 70b are sized to fit within mounting 
collars 72a, 72b located at one end of each mounting arm 24. The mounting 
collars 72a, 72b are made of metal and therefore grip the mounting posts 
70a, 70b sufficiently to prevent their inadvertent rotation within the 
mounting collars 72a, 72b. The other end of each mounting arm 24 includes 
a second mounting collar 76 which receives a mounting post 78 that extends 
from an adjustable table mount 80. The mount 80 is slidably mounted on 
side rail 22. This arrangement provides for adjusting the horizontal 
separation between support bar 20 and end 82 of table 12. 
As shown in FIG. 2, the head support 10 can be used to secure the head 90 
of a patient in a desired, fixed relationship to an x-ray source 92. 
Cradle 30 may be rotated for rotational adjustment of the head within 
U-clamp 14 and the patient's head 90 can be secured within the clamp 14 at 
the desired position. Likewise, knobs 40, 45, and 54 may be used to 
further adjust the vertical and horizontal displacement of the patient's 
head with respect to the patient support table 12. Further horizontal 
adjustment with respect to support table 12 is provided through the 
release and tightening of locking screw 61 in support aperture 60 for the 
horizontal movement of mounting bracket 18 of support bar 20. As evident 
in FIG. 2, the head support 10 securely holds the patient's head without 
significant slippage between radiolucent components of the head support 
and without interposing the radiopaque mounting arms 24 between the x-ray 
source 92 and the x-ray film (not shown) which is usually located below 
the head support 10. 
While a preferred embodiment of the present invention has been described, 
further modifications and changes would be apparent to one of ordinary 
skill in the art without departing from the principles of the invention. 
It is intended that all such changes and modifications obvious to one of 
ordinary skill in the art be covered by the appended claims.