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Magnetic Resonance Imaging

Magnetic Resonance Imaging Quick Links Safety Concerns in MRI/Inpatient MRI Screening MRI Section MRI of the Abdomen Cardiac Magnetic Resonance MRI of Musculoskeletal System MRI of the Pelvis MRI of the Spine (Body) MRI of the Thorax Magnetic Resonance Body Angiogram MRI of the Spine (Neuro) MRI of the Brain MRI of the Neck
Magnetic Resonance Temporomandibular Joint Neuro Magnetic Resonance Angiogram (MRA)

 

MRI SECTION

 

Introduction:

Magnetic resonance imaging uses a high strength super-conducting magnet to orient protons within the body. The radio frequency energy is directed into the patient by the RF transmitting coil. This causes a change in the quantum spin state of the proton nucleus, which is promoted to a higher spin state. As the higher spin state nuclei relax, they emit radiowaves which are then detected by the receive coil. At the same time that the radio frequency emission is occurring from the nuclei, gradients are applied to help encode spatial information. This data is then processed in a computer using Fourier transforms to obtain spatial data, which has both image signal intensity data as well as phase information. Phase data can be used to quantify velocity in flowing regions.

Because of the way the device works, there are two potential problems with patient implants. First pacemakers and electromagnetic devices (devices that cause electrical currents to be connected to tissue) can be altered in their frequency and voltage when used in an electromagnetic field. Second, implants or foreign bodies having a high iron content may torque and move in the magnetic field causing focal tissue disruption. A careful evaluation of the patient's surgical history and previous trauma is necessary prior to referral to the MRI center. If patients have had a history of welding, either a plain film evaluation or a dedicated orbital CT is performed prior to an MR examination due to the high frequency of intraocular or extraconal metallic fragments.

MRI does not use ionizing radiation. For that reason there are no known teratogenic effects of magnetic resonance imaging at this point in time. However, we do not recommend imaging patients in the first trimester of pregnancy. This is because there is local heating, which does occur with the application of RF pulses. This heating could potentially disrupt normal organogenesis. There is no current scientific data showing any dose response relationship between defective organogenesis and the application of RF pulses.

MRI is the imaging method of choice for portions of the body that contain water and stay still (brain, spine, neck, liver, pelvis, extremity, bone marrow). The resolution obtained with MR is dependent on field strength, the local gradient coils, and surface coils. Our current resolution, however, is on the order of a 10th of a millimeter with whole-body images. For structures that move (the heart, the liver and the aorta) MR has to be used carefully and with various motion control software such as cardiac gating. For regions of the body that contain too few protons (i.e., the lungs) MR is not as useful as computed tomography (CT) for evaluating and characterizing lesions. One should remember that a plain radiograph or angiogram has much higher spatial resolution than routine MRI.

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MAGNETIC RESONANCE IMAGING OF THE ABDOMEN

 

Description:

While the patient is supine on the table gantry within the magnet, a series of MR sections are obtained through the region-of-interest in the abdomen. These sections can be obtained in any plane. RF pulse sequence techniques can be varied so that the resultant images highlight fat, water, or a combination of both (proton density). Patients may be asked to suspend respiration.

Indications:

1. Evaluation of focal or diffuse disease of the liver, spleen, pancreas kidneys adrenal gland or gallbladder.
   
   
2. Evaluation of the abdominal aorta and inferior vena cava.
   
   
3. Lymphadenopathy.
   
   
4. Detection and characterization of other retroperitoneal/peritoneal processes.

Contraindications:

1. See Appendix A for implanted devices that are metallic or electromagnetic.
   
   
2. Pregnancy (relative).



3. Claustrophobia (relative).
   
   
4. Uncooperative patients from any cause should be adequately sedated prior to sending to MRI. Patient must be able to hold still for at least ten minutes to allow for an adequate examination. Please notify and arrange with MRI personnel.

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CARDIAC MAGNETIC RESONANCE

 

Description:

Evaluation of the heart is performed well with MRI using cardiac gated spin echo pulse sequences as well as cine MR pulse sequences. Cine MR pulse sequence allow for rapidly flowing blood to be visualized as high signal intensity material. In addition, the velocities and flow rates can be obtained. SPAMM pulse sequences allows for the quantitative assessment of subsegmental myocardial function. The role of MR contrast agents for the investigation of myocardial perfusion is now underway in animals.

Indications:

1. Anatomy of the heart and great vessels for congenital heart disease.
   
   
2. Bi-ventricular function analysis.
   
   
3. Shunt size evaluation.
   
   
4. Evaluation of the aortic root and great vessels in case of dissection.
   
   
5. Pulmonary arterial flow and evaluation or mural thrombi.
   
   
6. Pulmonary arteries in cases of pulmonary arterial hypertension.
   
   
7. Patency of the inferior and/or superior vena cava.

Contraindications:

1. Pacemakers (See appendix A).
   
   
2. Severe EKG disturbances.
   
   
3. Hemodynamically unstable patients.
   
   
4. Starr-Edwards prosthetic heart valves.
   
   
5. Pregnancy.

Preparations:

Arrangements for uncooperative patients should be made with MRI personnel.

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MAGNETIC RESONANCE IMAGING OF MUSCULOSKELETAL SYSTEM

 

Description:

Using surface coils, or body coil, images of the musculoskeletal system can be obtained with extremely high resolution. For imaging of the shoulder, knee, spine, wrist, ankle and the long bones of the appendicular skeleton are extremely well evaluated with MR. For most diagnoses it is the diagnostic modality of choice after plain film examination.

Indications:

1. Bone tumor.



2. Avascular necrosis.



3. Evaluation of bone marrow disorders.



4. Occult fractures.



5. Evaluation of muscle and tendon disorders.



6. Evaluation of cartilage and ligament abnormalities.



7. Evaluation of osteomyelitis.

Contraindications:

1. Ferromagnetic foreign bodies and electromagnetic implants (see Appendix A).



2. Pregnancy.



3. Claustrophobia.



4. Uncooperative patients - these should be sedated.

Preparation:

None

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MAGNETIC RESONANCE IMAGING OF THE PELVIS

 

Description:

A series of images can be obtained in multiple planes of the pelvis using both the body coil in the send-receive mode or through intracavitory coils. This allows for extremely high-resolution images of the prostate and cervix and the rectal wall.

Indications:

1. Any pathology of the uterine corpus or cervix.



2. Ovarian pathology.



3. Rectal pathologies.



4. Prostatic disease (both congenital and acquired).



5. Diseases of the bladder.



6. Renal transplant.



7. Renal neoplasms.



8. Pelvic venous or arterial abnormalities.

Contraindications:

1. Ferromagnetic foreign bodies and/or electromagnetic implants. (see Appendix A).



2. Pregnancy.



3. Claustrophobia (relative).



4. Uncooperativity.

Preparation:

None

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MAGNETIC RESONANCE IMAGING OF THE SPINE (BODY)

 

Description:

The MR imaging of spinal disease is split between the neuroradiology department and the body MR imaging section. Disease related to the spinal cord and/or nerve roots are usually serviced through the neuroradiology department. Otherwise, routine disc disease and bony problems are serviced through the body MR division and the musculoskeletal division or through the Neuro MRI division.

Indications

1. Suspected disk disease (herniation, infections, bulge).
   
   
2. Evaluation for metastases, vertebral compression fractures or vertebral compression related to metastatic disease.
   
   
3. Suspected scar postoperatively.

Preparation:

Intravenous antibiotics are administered prior to the examination.

Complications:

1. Ferromagnetic foreign bodies and/or electromagnetic implants (see Appendix A).
   
   
2. Pregnancy.
   
   
3. Claustrophobia (relative).
   
   
4. Uncooperative patients (should be sedated prior to sending to MRI).

Preparation:

The preparation required for the spinal MR is minimal. If the patient cannot hold still, some form of sedation is strongly suggested. Call MRI personnel.

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MAGNETIC RESONANCE IMAGING OF THE THORAX

 

Description:

For thoracic imaging, it is important that the patient be cooperative. Both electrocardiographic gating and respiratory gating are used to help reduce motion artifacts during the examination. In addition, the patient will be asked to suspend respiration for a minimum of 10 seconds during the exam. Patients who are extremely apneic yield poor MR images in the chest.

Indications:

1. Thoracic mass.
   
   
2. Mediastinal mass.
   
   
3. Mediastinal anatomy.
   
   
4. Pulmonary vessel anatomy and flow.
   
   
5. Evaluation of suspected pulmonary arterial venous malformation.
   
   
6. Evaluation of bronchogenic cysts.

Contraindications:

1. Ferromagnetic foreign bodies and/or electromagnetic implants (see Appendix A).
   
   
2. Pregnancy.
   
   
3. Claustrophobia (relative).
   
   
4. Tachypnea (relative).

Preparation:

None

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MAGNETIC RESONANCE BODY ANGIOGRAM

 

Description:

MR angiographic techniques may be acquired either with or without contrast enhancement. Contrast-enhanced magnetic resonance IR is now the state of the art MR technique for evaluation of the vessels of the chest, abdomen and pelvis. Unlike conventional arteriography, MR IR does not require arterial access, uses no ionizing radiation and avoids potentially nephrotoxic iodinated agents. Even patients with know severe contrast allergies can undergo contrast enhanced MR IR because the safety profile of the MR contrast (Gadolinium DTPA) is much higher than the iodinated contrast agents used in conventional arteriography.

Indications:

Suspected disease in aorta, visceral or peripheral circulation.

Contraindications:

1. Ferromagnetic foreign bodies and/or electromagnetic implants (see Appendix A).
   
   
2. Pregnancy
   
   
3. Claustrophobia
   
   
4. Tachypnea (relative)

Preparation:

None

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NEURO MRI MAGNETIC RESONANCE IMAGING OF THE SPINE

 

Description:

The MR imaging of spinal disease is split between the neuroradiology department and the body MR imaging section. Diseases related to the spinal cord and/or nerve roots are usually serviced through the neuroradiology department. Routine disc disease may be evaluated by either the Body or Neuro group. Contrast agent (Gadolinium DTPA) may be injected to provide added information.

Indications:

1. Suspected disc disease (herniation, infections, bulge).
   
   
2. Evaluation for metastases, vertebral compression fractures or vertebral compression related to metastatic disease.
   
   
3. Suspected scar postoperatively.
   
   
4. Suspected cord disease.
   
   
5. Suspected spinal stenosis.
   
   
6. Spinal or paraspinal tumors.

Contraindications:

1. Ferromagnetic foreign bodies and/or electromagnetic implants (see Appendix A).
   
   
2. Pregnancy.
   
   
3. Claustrophobia (relative).
   
   
4. Uncooperative patients (should be sedated before sending to MRI).

Preparation:

The preparation required for the spine MR is minimal. If the patient cannot hold still, some form of sedation is strongly suggested. Call MRI personnel before sending patient.

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MAGNETIC RESONANCE IMAGING BRAIN

 

Description:

MRI is a highly sensitive modality for imaging the brain. Images are obtained in multiple planes. Contrast agent (Gadolinium DTPA) may be injected to provided added information

Indications:

All intracranial pathology.

Contraindications:

1. Ferromagnetic foreign bodies and/or electromagnetic implants (see Appendix A).
   
   
2. Pregnancy.
   
   
3. Claustrophobia (relative).
   
   
4. Uncooperative patients (should be sedated prior to sending to MRI).

Preparation:

The preparation required for the head MR is minimal. If the patient cannot hold still, some form of sedation is strongly suggested.

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MAGNETIC RESONANCE IMAGING NECK

 

Description:

Images are obtained in multiple planes. Contrast agent (Gadolinium DTPA) may be injected to provide added information.

Indications:

1. All neck masses.
   
   
2. Base of the skull pathology.
   
   
3. Salivary gland masses.
   
   
4. Laryngeal, pharyngeal, and tracheal masses.
   
   
5. Tongue masses.
   
   
6. Sinonasal masses.

Contraindications:

1. Ferromagnetic implants and/or electromagnetic devices. (see Appendix A).
   
   
2. Pregnancy.
   
   
3. Severe claustrophobia.
   
   
4. Inability to tolerate supine position because of airway obstruction and/or dyspnea.
   
   
5. Uncooperative patients.

Preparation:

The preparation required for Neck MR is minimal. If the patient cannot hold still, some form of sedation is strongly suggested.

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MAGNETIC RESONANCE TEMPOROMANDIBULAR JOINT

 

Indications:

1. Meniscal Abnormalities.
   
   
2. Joint dislocation or TMJ syndrome.
   
   
3. Suspected avascular necrosis of mandibular condyle.
   
   
4. Suspected joint effusion or inflammation.

Contraindications:

1. Ferromagnetic implants and/or electromagnetic devices.
   
   
2. Pregnancy.
   
   
3. Severe claustrophobia.
   
   
4. Inability to tolerate supine position because of airway obstruction and/or dyspnea.
   
   
5. Uncooperative patients.

Preparation:

The preparation required for TMJ MR is minimal. The patient, with the assistance of a mouth device, will be asked to hold mouth in open and closed position.

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NEURO MAGNETIC RESONANCE ANGIOGRAM (MRA)

 

Description:

MRA for the patient is performed like a Head or Neck MRI. It is often performed without IV contrast, but contrast may be used in many cases. MRA may demonstrate vascular lesions routinely seen at conventional IR. Its efficacy in diagnosing small aneurysms (<3-5 min.) or vascular malformations is still less than that of conventional IR, which is still considered the gold standard and the most appropriate way to evaluate patients for some vascular abnormalities, particularly aneurysms and AVMs and vasculitis. However, MRA is a good screening tool for aneurysms, carotid stenosis/occasional dissection, intracranial stenosis/occlusion, and dual sinus thrombosis.

Indications:

1. Suspected intracranial aneurysms.
   
   
2. Suspected intracranial arteriovenous malformations.
   
   
3. Evaluation of vascular supply to masses.
   
   
4. Evaluation of venous thrombosis.
   
   
5. Evaluation for cervical carotid stenosis, atherosclerotic narrowing.

Contraindications:

1. Ferromagnetic implants and/or electromagnetic devices.
   
   
2. Pregnancy.
   
   
3. Severe claustrophobia.
   
   
4. Inability to tolerate supine position because of airway obstruction and/or dyspnea.
   
   
5. Uncooperative patients.

Preparation:

The preparation required for the MR IR is minimal but the imaging techniques are even more sensitive to patient motion. If the patient cannot hold still, some form of sedation is strongly suggested.

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