During a MRI scan, pictures of almost all the tissue in the body are taken. The tissue that has the least hydrogen atoms, such as the bones turns out dark. The tissues that have many hydrogen atoms, such as fatty tissue looks much brighter. The timing of the radio wave pulses is constantly changed to gain information about the different types of tissues present. An MRI scan is normally used as an extremely accurate method of disease detection and structural abnormalities throughout the body.
Patient with any metallic materials within the body must notify their physician prior to the MRI scan. This is because, metallic chips, materials, metal implants, surgical clips or foreign materials (artificial joints, metallic bone plates or prosthetic devices, etc) can significantly distort the images obtained by an MRI scanner. Patients with pacemakers, metal chips or clips in and around the eyeballs cannot be scanned by an MRI because of the risk that the magnet may move the metal in these areas. Patients with artificial heart valves, metallic ear implants, bullet fragments and chemotherapy or insulin pumps should not undergo MRI scanning.
MRI scan can cause a small risk to the fetus in the first 12 weeks of pregnancy. Therefore scans are not performed on pregnant women. The MRI machine produces loud thumping and humming noise when the procedure is performed. Therefore ear plugs are usually given to the patients to reduce the noise. MRI scans are a useful aid in the assessment of certain back conditions. MRI is an aid to detail studies of nerve root injuries like lumbar disc herniation and lumbar spinal stenosis. It is also extensively used in spinal disc and lumbar disc diseases and isthmic spondylolisthesis. It is also useful to rule out tumors and spinal infections.
The heart works on the natural electrical impulses by the cardiac conduction system. An electronic pacemaker is surgically implanted in some patients suffering from cardiac arrhythmia to regulate the heart rhythm. This is done with electrical impulses generated by the pacemaker. The pacemaker system is made up of a battery pack and a couple of thin wires. The small generator is implanted under the skin. This is connected to the heart through tiny wires. The pacemaker ensures regular impulses to the heart so that they appear just like the natural pacemaker of the heart.
Demand pacemakers are those that are used only when needed. They have sensors that that kick off their pacemaker when the heart rhythm is slower than the required rate. Rate-responsive cardiac pacemakers automatically regulate the heart beat according to the body's need. It is imperative to check the functioning of the pacemaker regularly. The doctor will also need to detect any signs of the batteries wearing off. Certain medications, electrical device or electromagnetic noise can interfere with the working of the cardiac pacemaker. Handheld metal detectors, cellular phones and MRI can affect the pacemaker.
Andersen Tawil Syndrome
Andersen Tawil syndrome or ATS is a rare disease characterized by three distinct features that include: periodic paralysis or episodes of muscle weakness, cardiac arrhythmia and distinct facial and skeletal features. However all the three features may not be present in a single patient. Most ATS cases are caused by a mutation in the KCNJ2 gene; other cases result from unknown causes. KCNJ2 gene forms a channel that is responsible for transporting potassium ions into muscle cells. The movement of these ions is essential for maintaining the normal function of muscles. KCNJ2 gene mutations disrupt the structure of the potassium ions and leads to periodic paralysis and irregular heart rhythm.
Periodic paralysis: Anderson Tawil syndrome patients may experience episodes of flaccid paralysis. The lower and the upper limbs normally get affected and the paralysis may remain for short duration or continue for days. The severity and frequency varies from person to person and from episode to episode.
Heart arrhythmia: Anderson Tawil syndrome patients typically present with long QT interval, a disorder of the heart's electrical activity. It can cause sudden, uncontrollable, dangerous arrhythmia in response to exercise or stress.
Distinct Facial or skeletal features: Patients with ATS commonly develop physical abnormalities such as a small lower jaw, dental abnormalities, widely spaced eyes, short stature and curvature of the spine.
Diagnosis and treatment
Examining the clinical features, serum test to assess potassium levels, electrocardiogram to test the heart's electric activity and molecular genetic testing together help in establishing the diagnosis of Anderson Tawil syndrome.
There are no standard protocols laid out for treating ATS because of the rarity of the condition. Treatment of the Anderson Tawil syndrome depends upon the symptoms of the patient. If the patient is suffering from potassium sensitive periodic paralysis, potassium supplements are prescribed to rectify the levels.
However periodic paralysis caused by higher potassium levels resolve on their own in a short while. Of late, drugs known as carbonic anhydrase inhibitors are being used successfully to treat periodic paralysis in individuals with Andersen-Tawil syndrome. Cardiac arrhythmia is normally treated with beta adrenergic blockers and more complicated cases might need pacemakers and implantable defibrillator to prevent sudden cardiac deaths.
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Bibliography / Reference
Collection of Pages - Last revised Date: October 29, 2020