Note: Providers should seek information related to National Coverage
Determinations (NCD) and other Centers for Medicare & Medicaid Services (CMS)
instructions in CMS Manuals. This LCD only pertains to the contractor's
discretionary coverage related to this service.  
  
This policy addresses standard CT and MR imaging. _Magnetic Resonance
Angiography (MRA) is not addressed in this policy._

**Computerized Tomography (CT)**  
Computerized tomography (CT scanning) uses the attenuation of an x-ray beam by
an object in its path to create cross-sectional images. As x-rays pass through
planes of the body, the photons are detected and recorded as they exit from
different angles. Computers process the signals to produce a cross-sectional
view of the body. The signal data may be subjected to a variety of post-
acquisitional processing algorithms to obtain a multiplanar view of the
anatomy.  
  
The use of the CT scan must be found medically appropriate considering the
patient's symptoms and preliminary diagnosis.

  1. A CT scan is considered reasonable and necessary for the patient when the diagnostic exam is medically appropriate given the patient's symptoms and preliminary (or provisional) diagnosis.
  2. CT scans (as opposed to MRI evaluations) are used effectively in the following situations or conditions: 
    1. Patients who are not suitable candidates for MRI evaluation: 
      1. Because of a pacemaker or intracranial metallic objects
      2. Because of extreme obesity
      3. Because of an inability to lie still
    2. Patients whose condition requires the visualization of fine bone detail or calcification
    3. Patients with the following conditions 
      1. Acute CNS Hemorrhage
      2. Strokes or encephalomalacia
      3. New onset seizures, particularly if a focal component is present (contrast agent is appropriate for these patients)
      4. Intracranial (sic) lesions large enough to cause increased intracranial pressure (CT scan is useful to determine gross margins between tumor and edematous brain)
  3. There is no general rule that requires other diagnostic tests to be tried before CT scanning is used. However, in individual cases it may be determined that use of a CT scan as the initial diagnostic test was not reasonable and necessary because it was not supported by the patient's symptoms or complaints as stated on the claim.
  4. CT imaging has not been useful in general for the evaluation of headache or dizziness and should be reserved for the patient whose presentation indicates a focal problem or who has experienced a significant change in symptomatology.
  5. A CT scan for the diagnosis of headache can be allowed for the following: 
    1. After a head injury to rule out intracranial bleeding
    2. Headache unusual in duration (greater than two weeks) not responding to medical therapy, to rule out the possibility of a tumor
    3. A headache characterized by sudden onset and severity to rule out the possibility of an aneurysm, bleeding and/or arteriovenous malformation
  6. A CT Scan may be ordered without contrast, with contrast, or without contrast followed by contrast. Contrast administration is not without risk to the patient, and for some conditions, adds little or no benefit to the patient. The general indications for use of contrast CT scanning (as opposed to non-contrast scanning) are to: 
    1. Assess perfusion (e.g. CVA)
    2. Characterize a specific lesion
    3. Detect defects in blood/brain barrier (e.g. infarct, tumor, infection, vasculitis)
    4. Detect neovascularity (tumor), and
    5. For staging of known lung cancer, breast cancer, and lymphomas likely to metastasize early to the brain
  7. Intravenous contrast generally adds no information to CT scans done secondary to head trauma. Additional symptoms suggesting a possible intracranial bleed may justify the use of contrast. These symptoms should be documented in the medical record, and if appropriate, included in the diagnostic codes listed on the claim.
  8. More than one contrast CT scan per episode of illness adds no information with the following exceptions: 
    1. CVA
    2. Non-traumatic hemorrhage
    3. TIA
    4. Post-operative scan for residual tumor or post operative complication
    5. Known brain tumor/metastases with a change in mental status or other evidence of CNS change

  
**Magnetic Resonance Imaging (MRI)**  
Magnetic Resonance Imaging (MRI) is a non-invasive diagnostic scanning
technique that employs a powerful and highly uniform static magnetic field,
rather than ionizing radiation, to produce images. Fluctuations in the
strength of the magnetic field alter the motion and relaxation times of
hydrogen molecules, which are related to the density of molecules and reflect
the physicochemical properties of the tissues. Reconstructed images can be
displayed in multiple planes to facilitate analysis. **See national non-
coverage in CMS section above.**  
  
Coverage is limited to those CT and MRI machines that have received pre-market
approval by the FDA. Such units must be operated within the parameters
specified by the approval.  
  
Inconclusive findings on a CT scan may warrant a MRI study and, conversely,
findings of a MRI study may be further clarified (under certain circumstances)
with a subsequent CT scan. The information provided by the two modalities may
be complementary.  
  
Cancer Staging. Clinicians commonly use CT and MRI of the brain when
metastatic involvement is suspected.  
  
Non-covered indications: esophagus, oropharynx, and prostate, and non-melanoma
skin cancer in the absence of symptoms of brain involvement. "Certain tumors
almost never metastasize to the brain parenchyma. These include carcinomas of
the esophagus, oropharynx, and prostate, and non-melanoma skin cancers."
(DeVita, Chapter 52.1) Accordingly, the related diagnoses found in the
following diagnosis code list do not justify brain scans for "staging"
purposes unless a patient has signs or symptoms suggesting brain involvement.
Covered: In contrast, for those malignancies that commonly metastasize to the
brain, staging in the absence of neurological findings may be appropriate.  
  
Payment will be allowed for reasonable and necessary scans of different areas
of the body that are performed on the same day and are not subject to this
policy.

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