Foley catheters utilized to drain the bladder typically have no or few metallic components. Accordingly, these devices tend to be acceptable for patients undergoing MR procedures. However, certain Foley catheters have sensors to measure the temperature of the urine in the bladder, which is an appropriate means of determining “deep” body or core temperature. This type of Foley catheter usually has a thermistor or thermocouple located on or near the tip of the device and a wire that runs the length of the catheter to a connector that plugs into a temperature monitor. Sometimes an additional external cable is also used, which may or may not be removable. To date, a Foley catheter with a temperature sensor should never be connected to an external cable and/or the temperature monitor because this equipment has not been shown to be safe for patients undergoing MR examinations.

Several Foley catheters with temperature sensors have been evaluated for MRI issues by determining magnetic field interactions, heating, and artifacts. In general, the findings indicated that it would be acceptable to perform MR procedures in patients with certain Foley catheters with temperature sensors as long as specific recommendations and conditions are followed.

Similar to other devices with conductive components, the position of the wire and/or cable associated with the Foley catheter with a temperature sensor has an important effect on the amount of heating that develops during an MR procedure. Therefore, to prevent excessive heating associated with an MR examination, a Foley catheter with a temperature sensor must be positioned in a straight configuration (without a loop) down the center of the MR system and away from transmit RF coil or inside of the bore of the scanner. The metal connector, cable, or wire, must not touch the patient. Typical recommendations for the specific Foley catheters with temperature sensors that have undergone MRI testing include, the following:

• If the Foley catheter with a temperature sensor has a removable connector cable or extension, it should be disconnected prior to the MR procedure.
• Remove all electrically conductive material from the bore of the MR system that is not required for the procedure (i.e. unused surface coils, cables, etc.).
• Keep electrically conductive material that must remain in the bore of the MR system from directly contacting the patient by placing insulation or space between the conductive material and the patient.
• Position the Foley catheter with a temperature sensor in a straight configuration down the center of the MR system table to prevent cross points, coils, and loops.
• Ensure that the connector, cable, or wire does not touch the patient.
• MR imaging should be performed using MR systems shown to be acceptable and safe for patients (e.g., operating at a specific static magnetic field and frequency, 1.5-Tesla/64-MHz, or other tested field strength/frequency level) and all pertinent safety guidelines must be followed.
• Follow the Instructions for Use for a given Foley catheter with a temperature sensor with regard to the MR system reported, whole body averaged specific absorption rate (SAR).

Specific labeling instructions for a given Foley catheter with temperature sensor must be carefully followed. Importantly, not all Foley catheters with temperature sensors are acceptable for patients undergoing MR procedures.

An example of specific instructions for a Foley catheter with temperature sensor that has MRI labeling approved by the Food and Drug Administration is, as follows:

Foley Catheter with Temperature Sensor, Bardex Latex-Free Temperature-Sensing 400-Series Foley Catheter (C. R. Bard, Inc., www.bardmedical.com)

MRI Safety Instructions

Warning: This product should never be connected to the temperature monitor or connected to a cable during an MRI procedure. Failure to follow this guideline may result in serious injury to the patient. Refer to Instructions for Use. It is important to closely follow these specific conditions that have been determined to permit the examination to be conducted safely. Any deviation may result in a serious injury to the patient.

Non-clinical testing demonstrated that these Foley catheters with temperature sensors are MR Conditional. A patient with one of these devices can be scanned safely, immediately after placement under the following conditions:

• Static magnetic field of 1.5-Tesla or 3-Tesla with regard to magnetic field interactions.
• Spatial gradient magnetic field of 720-Gauss/cm or less with regard to magnetic field interactions.
• Maximum MR system reported, whole-body-averaged specific absorption rate (SAR) of 3.5-W/kg at 1.5-Tesla or 3-W/kg at 3-Tesla for 15 minutes of scanning (i.e. per pulse sequence).

Importantly, the MRI procedure should be performed using an MR system operating at a static magnetic field strength of 1.5-Tesla or 3-Tesla, ONLY. The safe use of an MR system operating at lower or higher static magnetic field strength for a patient with a Foley catheter with temperature sensor has not been determined.

Special Instructions: The position of the wire of the Foley Catheter with Temperature Sensor has an important effect on the amount of heating that may develop during an MRI procedure. Accordingly, the Foley catheter with temperature sensor must be positioned in a straight configuration down the center of the patient table (i.e. down the center of the MR system without any loop) to prevent possible excessive heating associated with an MRI procedure.

Additional safety instructions include the following:

1. The Foley catheter with temperature sensor should not be connected to the temperature monitoring equipment during the MRI procedure.
2. If the Foley catheter with temperature sensor has a removable catheter connector cable, it should be disconnected prior to the MRI procedure.
3. Remove all electrically conductive material from the bore of the MR system that is not required for the procedure (i.e. unused surface coils, cables, etc.).
4. Keep electrically conductive material that must remain in the bore of the MR system from directly contacting the patient by placing thermal and/or electrical insulation (including air) between the conductive material and the patient.
5. Position the Foley catheter with a temperature sensor in a straight configuration down the center of the patient table to prevent cross points and conductive coils or loops.
6. The wire and connector of the Foley catheter with temperature sensor should not be in contact with the patient during the MRI procedure. Position the device, accordingly.
7. MR imaging should be performed using an MR system with static magnetic strength of 1.5-Tesla or 3-Tesla, ONLY.
8. At 1.5-Tesla, the MR system reported whole body averaged SAR should not exceed 3.5-W/kg for 15-min. of scanning (i.e. per pulse sequence).
9. At 3-Tesla, the MR system reported whole body averaged SAR should not exceed 3-W/kg for 15-min of scanning (i.e. per pulse sequence).

In addition to the above, the Guidelines to Prevent Excessive Heating and Burns Associated with Magnetic Resonance Procedures should be considered and implemented.

MR healthcare professionals are advised to contact the respective manufacturer in order to obtain the latest safety information to ensure patient safety relative to the use of an MR procedure.

REFERENCES

Dempsey MF, Condon B, Hadley DM. Investigation of the factors responsible for burns during MRI. J Magn Reson Imag 2001;13:627-631.

Shellock FG. Magnetic Resonance Procedures: Health Effects and Safety. CRC Press, LLC, Boca Raton, FL, 2001.

Shellock FG, Kanal E. Magnetic Resonance: Bioeffects, Safety, and Patient Management. Second Edition, Lippincott-Raven Press, New York, 1996.

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