Imaging Techniques Used to Aid Diagnosis - Essay Example

?INTRODUCTION Magnetic Resonance Imaging (MRI) is one of the more commonly used imaging techniques used to aid diagnosis. It uses powerful magnets and radio waves to make images (Dugdale, 2010). However, emotional distress and lack of immobility not only lessen the quality of the resulting image, but it also causes adverse effects onto the health of the patient. Figure 1 shows an example of an MRI image from a moving patient. In such cases, use of sedation or general anesthesia is warranted to increase tolerance to an unpleasant but necessary procedure, and to expedite MRI imaging of a distressed patient (Medical Advisory Secretariat, 2003; Shellock, 2011). In fact, it has been shown that MRI images are better for children who were given general anesthesia. However, the effects of these drugs vary by age and disease of the patient (Medical Advisory Secretariat, 2003). Figure 1. An MRI image taken from a moving patient. From CT Dictionary [online] Available at: INDICATION FOR MONITORING Monitoring is important because staying close to the machine poses health risk to anesthesiologist or nurse assistant (Shellock, 2011). Monitoring is needed among patients who are high-risk, physically or mentally unstable patients, patients with abnormal physiologic functions, critically-ill, patients who are unable to communicated, such as sedated or anesthesized patients, neonatal or pediatric patients, patients undergoing MR-guided management, and patients who are at risk of having a reaction to contrast dyes or anesthesia. Monitoring allows anticipation of life-threatening conditions upon observation of minor changes in physiological functions (Shellock, 2011). Sedation poses greater threat among those at risk of respiratory and cardiac problems or any change in physiologic status as the sedated patient may get into respiratory depression or hemodynamic imbalance without being able to inform the MRI technologist. For pediatric patients, this is around 10% of children who underwent MRI (Shellock, 2011). In addition, injured or critically ill patients can acquire central nervous system or cardiorespiratory complications once given with anesthesia, and thus need close monitoring during the MRI procedure (Medical Advisory Secretariat, 2003). SELECTION OF PHYSIOLOGIC MONITORING PARAMETERS Vital and cardiorespiratory parameters are determined because these are usually altered during anxiety attacks. Changes in these body systems also manifest especially for ill patients exposed to this unusual environment. More importantly, these symptoms are commonly fatal once ignored (Medical Advisory Secretariat, 2003). Checking the temperature is important because anesthesia suppresses the regulation of core body temperature, which is controlled by the hypothalamus. Although fluctuations normally occur because of diurnal, internal and external factors, the body’s temperature is maintained between 36°C to 38°C. Hypothermia results from failure of these regulatory mechanisms, and this manifests as hypovolemia, myocardial ischemia, cardiac arrhythmia, pulmonary edema, decreased cerebral blood flow, and even death. In contrast, drug-induced malignant hyperthermia may also occur. Specifically, an abnormal increase in skeletal muscle oxidative metabolism happens, which overwhelms the body's capacity to oxygenation and carbon dioxide removal, as well as regulates body temperature. Malignant hyperthermia can eventually lead to circulatory collapse and death if not quickly identified and treated (Shellock, 2011). For any of the parameters to be checked, it is important that the sites at which they are measured has clinical relevance and provides a relatively fast response time to fluctuations, no matter how minute (Shellock, 2011). PERSONNEL Of course, the skilled MRI radiologist or technician should be present to operate the machine properly. In addition, the use of monitoring devices during the MRI procedure are of no use if there is no anesthesiologist or nurse anesthesist present within the vicinity to provide rapid evaluation and management once problems arise (Kempen). It is important to note that the one in charge of monitoring the physiologic signs of the patient should have no other responsibilities (Medical Advisory Secretariat, 2003). TECHNIQUES AND EQUIPMENT FOR MONITORING In the assessment of cardiovascular activity, electrocardiography (ECG), heart rate, and blood pressure are used. In recording ECG, it is important to get a baseline recording before the MRI imaging because the machine can cause changes in the waves of ECG, notably the T-waves or ST segments, which in turn may signal cardiac disorders (Shellock, 2012). Meanwhile, the heart rate can be measured using photoplethysmograph or pulse oximeter. Both blood pressure and heart rate can be measured using one technique, called the oscillometric method, which can get semi-continuous recordings. It is important to use the appropriate size of cuff so that the blood pressure can be measured accurately (Shellock, 2012). The blood pressure may be obtained using a special manual sphygmomanometer, which has a long tube from the cuff to the measuring device so that the one who takes it is at a safe distance away from the machine. Since mercury sphygmomanometers are already banned for use and the spring-gauge ones may be affected by MRI, the latter should undergo pre-clinical check before use in MRI setting (Shellock, 2012). Respiratory function is monitored by respiratory rate and oxygen saturation. Similar to ECG, respiratory rate can be measured by impedance method, which uses leads and cables. This is based on the difference in electrical impedance between the leads that correspond to inspiratory and expiratory movements. However, this may be unreliable for determining respiratory rate of pediatric patients as their thoraces are smaller in size. Similarly, a rubber bellow around the chest or waist measures respiration through the respiratory movement of the patient. These two techniques may not be able to detect apneic episodes due to upper airway obstruction. Capnometer, on the other hand, is a respiratory rate-measuring device that determines carbon dioxide levels at the end of the respiratory cycle (Shellock, 2012). Oxygen saturation is measured using pulse oximetry, which evaluates the oxygenation of tissues. Because oxygenated blood absorbs different amounts of light compared with deoxygenated blood, the amount of light absorbed by the blood can help determine oxygen saturation (Shellock, 2012). Thermometer is also included to measure the temperature. Fluoroptic monitoring system is more suitable in MRI environment than the commonly used thermistor or thermocouple-based techniques (Shellock, 2012). For emergency situations, a ventilator and other devices for first aid care should also present to provide increased air saturation. Currently, the mechanical switches, microprocessors and other components of ventilators are made up of ferrous material. Thus, it may be used only at a certain distance away from the MRI, or securely attached to the floor to prevent missile effects (Shellock, 2012). PATIENT PREPARATION FOR SEDATION History taking and physical examination should be conducted in order to anticipate conditions that the patient may be at risk of having after sedation. Nothing per orem should also be implemented six to two hours before the procedure. Determining the NPO period is important since sedatives relaxes the gag reflex. After administration and during the MRI procedure, the vital signs of the patient should be monitored. Figure 2. Example of ECG output during MRI. From Tse, Z., Dumoulin, C., Clifford, G., Oster, J., Jerosch-Herold, M., Kwong, R., Stevenson, W., and Schmidt, E. J. (2012). Cardiac MRI with Concurrent Physiological Monitoring Using MRI-Compatible 12-lead ECG. Journal of Cardiovascular Magnetic Resonance, 14(Suppl 1), p231. HAZARDS OF PHYSIOLOGICAL MONITORING IN MRI Missile effect Physiological monitoring equipment, emergency apparatus and hospital items such as oxygen cylinder, laryngoscope, intravenous poles, tables, chairs, light fixtures, and aspirator, is made up of ferrous materials that can easily be displaced by the magnetic field generated by MRI. As a result, these materials have potentially dangerous missile effects that can injure the patient once it is exposed to the MR environment. To prevent such occurrence, monitoring machines were modified to allow use in MR settings (Medical Advisory Secretariat, 2003; Dugdale, 2010; Shellock, 2011). . Undetected fatal changes because of inaccuracy of monitoring In addition, Liquid Crystal Display (LCD) screens or microprocessors in the patient monitoring system produce RF interference that affects MRI image quality. Light-emitting diodes and LCD terminals are likely to automatically turn on and off at a high frequency. In addition, the interference also radiates toward patient interface connections such as ECG leads and pulse oximetry through the imaging field, causing image distortion. These may make monitoring of the person inside less accurate (Medical Advisory Secretariat, 2003). Patient burns Moreover, the magnetic field may also overwhelm the magnet in the motors of some equipment, causing the motors to stop, slow down or accelerate. In addition, devices such as ECG electrodes, leads and pulse oximetry sensors, as well as metallic components like connectors, cables and surface coils can generate too much heat upon exposure to magnetic field. This may result to patient burns or fire in the equipment (www.mdsr.ecri.org/summary/detail.aspx?doc_id=8178, 1991; Medical Advisory Secretariat, 2003). Most commonly, these burns are located at areas in contact with a monitoring sensor, cable or accessory (www.mdsr.ecri.org/summary/detail.aspx?doc_id=8178, 1991). To resolve this, nonconductive materials, such as carbon fiber, fiberoptics and plastic tubing may replace the conductive leads commonly used for monitoring devices (www.mdsr.ecri.org/summary/detail.aspx?doc_id=8178, 1991; Medical Advisory Secretariat, 2003). EVALUATION OF COMPATIBILITY OF MONITORS MRI-compatible patient monitoring system can tolerate as much as 3 Tesla of magnetic field without any effects on the machine. In addition, multiple measuring devices were also put into one monitoring machine. For example, the Datex-Ohmeda system has ECG, pulse oximetry (SpO2), capnography, one non-invasive and two invasive blood pressure-measuring devices, as well as five anesthetic agents. However, the compatibility of these devices should be tested under actual conditions of use. Monitoring units may be placed outside the MRI room, or the screens may be shielded to prevent interference (Medical Advisory Secretariat, 2003). Several preparations can be done to prevent the possible adverse effects of monitoring during MRI. Before conducting the procedure, it should be ensured that leads and cables are not looped, the sensors, coils and cables as far away from one another as possible, all sensors and cables have intact electrical insulation, and no unnecessary sensors, cables and coils are present in the system (www.mdsr.ecri.org/summary/detail.aspx?doc_id=8178, 1999). For MRI equipment used in monitoring pediatric patients, the size- and age-appropriate machines and medications should be available and checked for functionality even before imaging is taken place (Medical Advisory Secretariat, 2003). Conclusion MRI is an important diagnostic technique needed in situations wherein the simpler imaging techniques are incapable of providing sufficient information about the disease. However, MRI is sometimes difficult to conduct, because it illicit anxiety attacks among susceptible patients, or because children cannot maintain immobility. These patients are thus given sedation or general anesthesia. This may present further problems, especially when patients cannot inform MRI technologists of the condition. Since the most common changes are cardiorespiratory in nature, parameters that measure these changes are monitored during MRI of highly susceptible individuals. However, the use of these monitoring devices during MRI poses further threats, such as missile effects and patient burns. To prevent such occurrences, ferrous materials are changed into its non-conductive counterparts. References CT Dictionary [online] Available at: Dugdale, D. C. (2010). MRI. [online] Available at: Kempen, P. M. ICU Patients Need Careful Monitoring in the MRI. [online] Available at: Medical Advisory Secretariat. (2003). Patient monitoring system for MRI: an evidence-based analysis. Ontario Health Technology Assessment Series, 3(7). Shellock, F. G. (2011). MRI Safety: Monitoring Body Temperature During MRI. [online] Available at: Shellock, F. G. (2012). Monitoring Patients in the MRI Environment. [online] Available at: Tse, Z., Dumoulin, C., Clifford, G., Oster, J., Jerosch-Herold, M., Kwong, R., Stevenson, W., and Schmidt, E. J. (2012). Cardiac MRI with Concurrent Physiological Monitoring Using MRI-Compatible 12-lead ECG. Journal of Cardiovascular Magnetic Resonance, 14(Suppl 1), p231. CT Dictionary [online] Available at: (1991). Thermal Injuries and Patient Monitoring during MRI Studies. [online] Available at: Read More