Question

What are some patient factors that may affect IR exposure? Explain in detail.

Answer 1

Patient Size
Fluoroscopy is restricted to patients who do not exceed the table weight limit, which varies by manufacturer but is generally 350 pounds. The maximum clearance between the table and image intensifier is approximately 45 cm. For larger patients, radiation dose is severely influenced by the patient’s body habitus.

Recall that half value layer is the amount of tissue that will reduce the quantity of X-rays to half the original number. At 60 kV, an increase in patient thickness by 3.5 cm doubles the number of X-rays required to penetrate the patient. It is important to ensure that the protocol selected prior to the procedure, which sets variables such as automatic brightness control and tube current, is appropriate for both the patient and procedure.

Pediatric Patients
The website imagegently.org provides an extensive discussion of fluoroscopy and radiation reduction techniques particular to the pediatric population.

Patient Position
Patient positioning during fluoroscopy is important to visualize anatomy, enhance image quality and optimize patient radiation dose. Radiation exposure is influenced by path through the body. Thus, orientations which yield high dose rates (i.e., tube angulation) should be used only when absolutely necessary.

The post-operative patient is a unique challenge for interventional radiologists. Prone position for a patient following laparotomy may not be feasible. In these cases, patient safety and comfort must be weighed against technical success of the procedure and radiation dose. If a decubitus position is necessary, the same methods to minimize radiation dose apply with the added caveat that the source should be furthest away from the operator.

Patient Cooperation
Patient cooperation is necessary when performing fluoroscopy. Patients are not only expected to remain motionless during the procedure, but also they may be asked to suspend respiration for periods up to 10-20 seconds.

Any patient movement creates motion artifact. To combat this, operators may repeat the imaging or increase the fluoroscopic frame rate, which both increase radiation dose. The patient’s ability to cooperate during the exam should be evaluated during the pre-procedure consent with anesthesia consultation, if necessary.

Pregnancy
On occasion, fluoroscopically guided procedures may be required during pregnancy. A consensus statement was produced by the Society of Interventional Radiology and the Cardiovascular and Interventional Society of Europe regarding radiation management for interventions using fluoroscopic or CT-guidance during pregnancy

As with all medical procedures, the benefits of the fluoroscopically guided procedure must exceed the potential radiation risks to the patient and fetus. The magnitude of the risk to the fetus is dependent on the fetus’ gestational age and the absorbed dose.

Radiation risks are most pronounced during pre-implantation, organogenesis and during the first trimester.The techniques to reduce radiation dose to the fetus are generally the same radiation reduction techniques used elsewhere. Additional considerations are to consider arm/neck access, decrease tube current (mA)/increase tube voltage (kVp) and use intravascular ultrasound.

Biologic Variation
Some patients are at risk for exaggerated radiation response because of an underlying condition. Prior exposure to high doses of radiation is perhaps the single greatest predictor of radiation injury. Repair of DNA injuries is usually complete by 24 hours, but repair and repopulation of damaged cells may take several months.

During the pre-procedure evaluation, patients should be screened for prior high-dose radiation, location and skin changes. Patients with active skin injury from prior radiation do occasionally require additional fluoroscopy. In this scenario, Balter et al. described the use of solder wire to delineate the area so that fluoroscopy could be avoided

In practice, radiopaque wires, catheters or dilators could also be used. Also, patients with diabetes mellitus, connective tissue disease and homozygosity for ataxia telangiectasia should be informed of an elevated risk of radiation injury