Info

— If possible, change over to a smaller image intensifier format (magnifier). An additional advantage here is the enlargement of the object.

— Use a saved radiation picture for documentation (indirect radiography).

Protection from scattered radiation

— Distance is the best radiation protection, because radiation decreases by the square of the distance.

— Use radiation protection clothing.

— Cover those parts of the patient's body which are not being examined.

4.2.4 Structure and technique of a surgical image intensifier

A modern surgical image intensifier consists of a mobile stand which can be moved with great precision millimetre by millimetre with very little effort. Cable deflectors are needed at all wheels. It must be possible to push it parallel to the operating table. The C-arm with the radiation source (generator) and the image receiver (image intensifier with camera) is positioned on this mobile stand in such a way that it can be moved and turned to all sides (7 Figs. 4.15-4.19). The C-arm has the largest possible inner width and penetration depth to make it easier to position it at the operating table. A laser light visor makes it easier to position the machine without radiation and helps during the locking nailing procedure. All functions required during the operation can be controlled from the control desk. A dose-optimised automatic function makes it easy to control the machine, improves image quality and reduces scattered radiation. The dose measuring system provides information about the applied patient dose.

The second component is the monitor trolley. This can also be moved with very little effort. It contains the image memory unit, image processing unit, both monitors and the documentation unit. Today the image memory unit and image processing unit consist of one single device and should be capable of storing at least 100 images. Image

Fig. 4.16. Movement transverse to the patient
D Fig. 4.17. Movement longitudinal to the patient, also possible by parallel displacement of the complete unit

Fig. 4.15. Orbital movement around the patient

I Fig. 4.18. Rotation of the C-arm

Fig. 4.15. Orbital movement around the patient

I Fig. 4.18. Rotation of the C-arm

Fig. 4.19. Adjusting the height

processing uses various filter techniques to produce high-contrast pictures at a low dose; these are then visually improved by subsequent image processing (e.g. electronic magnifier, Windows technology). When used in vascular surgery, image processing must be capable of performing subtraction procedures. A cinema function is available to assess these dynamic procedures which it records in the memory at differing recording speeds. The memory capacity should be at least 1000 pictures. For documentation purposes, integrated video printers can be used with thermal paper or foil, together with video recorders. State-of-the-art systems today are capable of transferring image data via a digital interface (DICOM) to a laser printer or digital archive (PACS). It should always be possible to transfer images to a digital data carrier (e.g. floppy disk, MO disk, CD-ROM) so that they can be processed in a conventional PC.

Today, two monitors are mandatory for surgical machines. For special applications (e.g. outpatients) where two monitors are not necessary, machines are available with just one monitor on the mobile stand. The complete image processing and memory functions are integrated in the mobile stand.

4.2.5 Application

Surgical image intensifies are used today in all surgical disciplines. They have become indispensable in the outpatients department, in orthopaedics, traumatology, neuro-surgery, general surgery, hand surgery, vascular surgery, for radiotherapy and endoscopy. An ongoing flow of new technology is constantly expanding the range of applications. Increasing possibilities for using the machines also make increasing demands on the staff who operate them. Some manufacturers have recognised this fact and offer special machines developed for certain applications, e.g. in the emergency room, on the intensive care unit or for gastroenterology.

Even the new navigation systems currently penetrating the market which used to need pictures produced with a CT can now produce comparable results when coupled with a C-arm.

4.2.6 Use of the surgical image intensifier

Before every operation, it is important to check that the machine is fully functional. After the patient has been positioned, in the case of difficult operations the machine should be positioned at the patient first without radiation. This is the only way to guarantee trouble-free use during the operation. The patient should be washed and covered only after this has been completed. An example for special positioning techniques is shown in O Fig. 4.20 and O Fig. 4.21.

As soon as the surgeon needs an X-ray picture, the machine should be brought into position, ensuring that the distance between image intensifier input and the patient is as short as possible. This not only improves image quality but also makes a contribution to radiation protection. The larger focal spot/skin distance reduces the radiation burden on the patient. Positioning without radiation is made easier in modern machines with a laser light visor. The X-ray program (organ automatic mode) is chosen. Everyone in the room must wear protective clothing. After the first X-ray has been taken, the position of the image on the monitor can be adjusted by reflecting and/or turning the picture. Modern machines rotate the image directly on the monitor. Rotation takes place by digital means in the image memory so that no additional radiation is required for position control. The object is then gated using the iris or slot diaphragm.

Automatic dose control usually ensures that there is a perfect image. The optimum dose is adjusted depending on the object. But metal implants or instruments in the ray path prevent the automatic dose control from working properly. In this case, it is advisable to press the automatic stop button and adjust the image manually. Some machines have a program which is capable of ignoring metal in the ray path during the control phase. This prevents radiating over the organs.

4.2.7 Tips and tricks for daily routine

Keep the radiation times as short as possible. A smaller image intensifier format (magnifier) reduces the radiation burden and makes it easier to recognise details. Store images with important interim results so that they are available later on for documentation. Whenever an image

has to be compared with another one (e.g. in two-level operation), transfer one image to the auxiliary monitor with the image change button. If the machine has to be re-positioned, never continue with radiation during the movement but use the laser light visor for re-positioning. After the operation, save the results in all necessary levels. If top quality is required for documentation, use digital radiography (snap shot) for the final images.

After the operation, document the necessary images. A video printer with thermal paper or foil can be used for this purpose; modern machines have a DICOM interface to produce the images directly on a laser printer or store them in a digital archiving system (PACS). Modern machines can also save the images on digital memories (e.g. floppy or MO disk or CD) so that they can be processed on any PC.

References

1. Richtlinie Fachkunde und Kenntnisse im Strahlenschutz für den Betrieb von Röntgeneinrichtungen in der Medizin, Zahnmedizin und bei der Anwendung von Röntgenstrahlen auf Tiere (Fachkunde nach Röntgenverordnung/Medizin) BArbBl. 9/90, S, 67 und BArbBl. 9/91, S. 88

2. Verordnung über den Schutz vor Schäden durch Röntgenstrahlen (Röntgenverordnung - RöV) vom 7. Januar 1987 in der Fassung der Bekanntmachung vom 30. April 2003 (BGBl. I S. 604)

3. Richtlinie 96/29/EURATOM des Rates vom 13. Mai 1996 (»EURATOM-Grundnormen«) zur Festlegung der grundlegenden Sicherheitsnormen für den Schutz der Gesundheit der Arbeitskräfte und der Bevölkerung gegen die Gefahren durch ionisierende Strahlungen, Amtsblatt der Europäischen Gemeinschaften DE Nr. L 159 vom 29 Juni 1996, S. 1

4. Richtlinie 97/43/EURATOM des Rates vom 30. Juni 1997 (»EURATOM-Patientenschutz-Richtlinie«) über den Gesundheitsschutz von Personen gegen die Gefahren ionisierender Strahlung bei medizinischer Exposition und zur Aufhebung der Richtlinie 84/466 EURATOM, Amtsblatt der Europäischen Gemeinschaften DE Nr. L 180 vom 9. Juli 1997, S. 22

5. Richtlinie für die technische Prüfung von Röntgeneinrichtungen und genehmigungsbedürftigen Störstrahlern - Richtlinie für Sachverständigenprüfungen nach der Röntgenverordnung (SV-RL) - vom 27. August 2003

6. Richtlinie zur Durchführung der Qualitätssicherung bei Röntgeneinrichtungen zur Untersuchung oder Behandlung von Menschen nach den §§ 16 und 17 der Röntgenverordnung - Qualitätssicherungs-Richtlinie (QS-RL) - vom 20. November 2003

7. Leitlinien der Bundesärztekammer zur Qualitätssicherung in der Röntgendiagnostik, Qualitätskriterien röntgendiagnostischer Untersuchungen (Überarbeitete und ergänzte Fassung), Deutsches Ärzteblatt 92, Heft 34/35, 28. August 1995 A 2272 - A 2285

8. DIN V 6868-57 Sicherung der Bildqualität in röntgensdiagnos-tischen Betrieben, Teil 57: Abnahmeprüfung an Bildwiedergabegeräten

9. Richtlinie für die physikalische Strahlenschutzkontrolle zur Ermittlung der Körperdosen, Teil 1: Ermittlung der Körperdosis bei äußerer Strahlenexposition (§§ 40, 41,42 StrlSchV; § 35 RöV) vom 08.12.2003

10. DIN 6813: 1980-07, Strahlenschutzzubehör bei medizinischer Anwendung von Röntgenstrahlen bis 300 kV; Regeln für die Herstellung und Benutzung

11. DIN EN 61331-3 Strahlenschutz in der medizinischen Röntgendiagnostik, Teil 3: Schutzkleidung und Gonadenschutz, Ausgabe Mai 2002

12. DIN 6809-7 Klinische Dosimetrie - Teil 7: Verfahren zur Dosisermittlung in der Röntgendiagnostik, Ausgabe Oktober 2003

13. Richtlinie »Ärztliche und zahnärztliche Stellen« (Richtlinie zur Strahlenschutzverordnung (StrlSchV) und Röntgenverordnung (RöV) vom 05.11.2003 (Anwendung ab dem 1. März 2004)

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