Annual Maximum Target Organ Permissible Radiation Dose Organ/Area The annual whole-body dose limit for physicians is 50 mSv. The maximum permissible dose (MPD) is the upper limit of allowed radiation dose one may receive without the risk of significant side effects (Table 1). The biological effects of radiation are caused by the ionization of water molecules within cells, producing highly reactive free radicals that damage macromolecules such as DNA. The unit of dose equivalent, under the SI system, is sievert (Sv). Radiation Equivalent Man (rem) is used to predict the biological effects from different types of radiation. It is defined as the quantity of radiation which results in an energy deposition of 1 joule per kilogram (1 J kg-1) within the irradiated material. Gray (Gy) is the term used under the International System of units (SI) as the principal unit for measurement of ionizing radiation dose. Rad (radiation absorbed dose) is the unit of measure that expresses the amount of energy deposited in tissue from an ionizing radiation source. ABC or Automatic Brightness Control system (Figure 3) occurs when the computer automatically analyzes the picture contrast and makes the appropriate tube current adjustments balancing picture contrast and patient safety.įigure 2. Control panel of the fluoroscopy machineįigure 3. Detailed picture of the control pane Higher kVp and tube current increase the total amount of x-ray radiation (see control panel of the fluoroscopy machine, Figure 2). Increased kVp increases the penetrability of the x-ray beam and decreases the contrast, producing brighter pictures. The quality of picture contrast depends on the balance between the kVp and the tube current. The x-ray tube occupies the inferior portion of the C-arm while the image intensifier is at the superior portion. The x-ray radiation that passes through the body enters the image intensifier where it is converted to a visible image that is displayed on the monitor screen (Figure 1).įigure 1. A typical fluoroscopy machine. The electrode-anode interaction produces energy that is converted to x–radiation. The high voltage (kilovolt peak, kVp) passes through the x-ray tube towards the positive electrode (anode). X-rays are generated by a current, measured in milliamperes (mA), passing through an electrically heated negatively charged filament (the cathode). In a national survey of pain medicine physicians, it was noted that 73% of private practices use fluoroscopy compared to 39% of academic institutions. Even though the success rate was high, it was noted that the needle was placed 1 or 2 spaces above or below predetermined level in 53% of the attempts and that the contrast reached the level of pathology in only 26% of the cases The number of attempts to successfully enter the epidural space was 2+1. It was noted that there was unilateral contrast spread in 51% of the injections.įor post-laminectomy patients, anesthesiologists successfully placed the epidural in 92% of the attempts. The authors recommended that epidurogram be performed to document position of the needle and to confirm that the medications are not injected intrathecally or intravenously.įor cervical epidural steroid injections, a multicenter, retrospective study showed 47% success on first attempt a second attempt was required in 63% of the patients. Caudal epidural steroid injections done by radiologists under fluoroscopy resulted in a success rate of 97.3%. A study on the use of fluoroscopy in caudal injections implied higher success rates. They noted that the most common site of incorrect needle placement was along the subfascial plane posterior to the sacrum. In a prospective observational study, senior PM&R physicians had a 74% success rate on their attempt, 88% when the landmarks were identified easily. Radiologists who performed less than 10 epidurals had a 48% failure rate. Success rates appear to be related to the experience of the radiologist however. įor caudal injections, “experienced radiologists” incorrectly place the needle in 38% of their epidural injections. Another study showed inaccurate needle placement in 17% of epidural injections performed by experienced anesthetists using the interlaminar technique, 85% of the injections were in the lumbar area. These incorrect placements occurred in 25% of caudal and 30% of interlaminar epidural steroid injections when performed by an experienced anesthesiologist and an orthopedic surgeon. Incorrect needle placements have been demonstrated when epidural steroid injections are performed without fluoroscopic guidance. Northwestern University Feinberg School of MedicineĬhicago, IL Needle Placement With and Without Fluoroscopy
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