Using the Lead Snake to Reduce Scatter Radiation

Introduction

The lead snake was designed to reduce scatter radiation associated with the horizontal ray lateral sternum projection. It was clear that when imaging thicker anatomical regions, and where there was primary X-ray beam making direct contact with the film/receptor, radiation scatter degradation of the image was considerable. This degradation was inevitable with the lateral sternum projection because it was otherwise impossible to collimate the primary beam within the skinline.

Related Wikiradiography Pages

http://www.wikiradiography.com/page/Lead+Snake+Construction+Notes

The Concept

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The idea of producing an articulated lead snake arose from observing children playing with a snake toy. When laid on its side, the snake toy would conform itself to the shape of the object it was laying on.

The Design

The Snake Articulated Lead Shield	The snake is made with 1mm lead sheet laminated between two pieces of grey PVC sheet. A threaded metal sleeve and two countersunk stainless steel bolts allow each piece to freely articulate and conform to any shape. Unlike lead rubber, the snake is made from solid lead sheet and is very effective at absorbing the primary X-ray beam.
The Snake showing lead and plastic Lamination

Using the Snake with the Lateral Sternum Projection

The snake was designed to be self conforming to the chest wall when used on the horizontal ray lateral projection of the sternum as shown below.

Snake positioned for a Horizontal Ray Lateral Sternum Projection

The snake is easily kept upright using a blanket which is laid across the top of the patient and covering the lower segment of the snake (not shown)

Lateral cross-table sternum using snake to reduce scatter radiation

Case 1

This patient presented to the Emergency Department following a head-on motor vehicle accident. The patient was experiencing considerable sternal pain and was referred for radiography of the sternum. These images were taken using conventional film-screen radiographic equipment.

	Image 1- No Snake This is the initial lateral sternum image. It is apparent that the there is underexposure in the lower sternum due to overlying breast shadow. There is also overexposure of the manubrium. The radiographer considered that the image was degraded by scatter radiation. She kept the exposure factors the same and repeated the image using the snake positioned over the sternum
	Image 2- Repeat View with Same Exposure with Snake In-situ This repeat view of the lateral sternum is clearly of a much higher quality. The higher quality of this repeat image can be almost completely attributed to the reduction in scatter radiation associated with the use of the snake. A fracture of the sternum with possible associated retro-sternal soft tissue swelling is now revealed

Case 2

This patient also presented to the Emergency Department following a head-on motor vehicle accident. A trauma radiographic series was requested including lateral sternum. The radiographer thought that the patient's very large breasts would cause considerable artifact if a lateral cross-table sternum projection was attempted. The risk of failure was so high that conventional cross-table lateral sternum radiography was considered likely to fail.

Following discussion with the doctor in attendance, it was decided that a lateral cross table sternum projection would be attempted using the snake and with taping of the breasts so that they were positioned anterior to the sternum. The "taped up" breasts held the snake in position. The patient freely consented to the procedure.

The resulting lateral cross-table sternum image is shown. The results are remarkably good in a patient who appeared to be to be unsuitable for cross-table sternum radiography. The distance between the visible snake segment and the sternum represents the thickness of the soft tissues anterior to the sternum. There is no evidence of breast tissue overlying the sternum. Clearly, there must be explicit consent from the patient to undertake this procedure. The positioning of the snake and the taping of the breasts was undertaken by a female member of the radiography staff.

Other Applications

Barium enema horizontal ray lateral rectum

Scatter radiation can degrade the barium enema horizontal ray lateral rectum view. The Snake is positioned as shown below

When used in conjunction with a graduated aluminium filter, the snake can effect a considerable improvement in image quality for this projection

Lateral Sacrum and Coccyx

The lateral sacrum and coccyx presents difficulties in terms of exposure technique. Whilst they can be imaged separately, there are advantages in demonstrating the anatomy in a single lateral projection in terms of efficiency and radiation protection. A comparison was made using a pelvis phantom to examine the difference that the combined use of a Snake and graduated aluminium filter would make on the visualised anatomy. Note that the exposure used on both images are identical. Note also that these images are radiographs (non-digital).

These 2 images are taken with the same exposure

Lateral Sacrum and Coccyx	Lateral Sacrum and Coccyx with Snake and Aluminium Filter

D.R. system lateral sacrum and coccyx with snake and aluminium filter

Using the Snake for Gonad Protection

	The snake has been utilized as gonad protection in a male patient. The advantages of using the snake for male gonad protection are as follows it is made of solid 1mm lead and is therefore suitable for absorbing primary beam unlike an offcut of lead rubber, it produces a neat result the shape of the snake can be changed so that it balances across the patient's legs If the inferior pubic rami are not required to be imaged (for example with fracture follow-up, or for hip joint pathology) the positioning of the snake can overly the inferior pubic rami. In cases of pelvis trauma, the snake should not overly bony anatomy (see below left) Dystrophic calcification noted immediately lateral to right hip
	This is appropriate positioning of gonad protection in pelvic trauma patients ( ? enchondroma, ? bone infarct left femur)
	Male gonad protection using the end of the snake.
	Male gonad protection using a shaped piece of scrap lead rubber. This is undeniably effective male gonad protection, but lacks some aesthetic appeal.

Conclusion

The snake has been in use in my department for 7 years. It has found wider application than its originally conceived application for lateral cross-table sternum radiography. The effectiveness and versatility of the snake has seen it earn its place in the radiographer's toolbox.

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