Neuroimaging DLA

Question 1

What are the advantages & disadvantages of X-rays?

Answer 1

• Advantages
– Inexpensive
– Commonly available
– Sensitive to skull fracture and dense foreign matter

• Disadvantages
– Exposure to ionizing radiation
– Brain structures minimally visible

Question 2

Define Cerebral Angiography (Vasography)

Answer 2

– X-ray representation of blood vessels with contrast medium applied through a catheter

Question 3

What are the risks of cerebral angiography (Vasography)?

Answer 3

– Allergic reaction

– Arterial spasm —>cerebral infarction

Question 4

What are the indications of Cerebral Angiography (Vasography)?

Answer 4

• Indications:
– Vascular malformations: Angioma (vascular tumor),
aneurysm

– Vascular obstruction, stenosis

Question 5

What is cerebral angiography?

Answer 5

• Cerebral angiography is an X-ray-based technique that images the arterial and venous systems of the brain.
• An intra-arterial catheter (e.g., femoral or cubital) advances to the carotid or vertebral arteries for administration of a contrast medium. Radiographs are taken while the dye passes through the arteries. Images are subsequently taken as the contrast medium passes through the venous system. Vascular abnormalities of the brain, like arteriovenous malformations and aneurysms, can thus be imaged.

Question 6

When is a myelogram used?

Answer 6

In myelography, the spinal cord, nerve roots and the subarachnoid space are examined. The myelogram is taken after injecting a contrast medium into the spinal subarachnoid space. Myelography reveals herniated (slipped) intervertebral disks and spinal tumors.

Question 7

What is the technique of CT scans?

Answer 7

In cranial CT scan, an X-ray source rotates around the head of the patient. X- ray sensors located opposite to the source continuously measure the attenuation of the X-radiation. The data are used to calculate a horizontal ‘slice’ (or tome) of the head.

Question 8

What are the indications of CT scans?

Answer 8

• Infarctions and intracranial hemorrhages are readily detected by CT. The procedure is initially performed without contrast agents, because contrast may resemble a bleed. A normal CT generally does not show an infarction in the acute stage but is commonly performed to exclude a hemorrhage.
• For diagnosing tumors, CT with contrast can be used inexpensively but are less sensitive than magnetic resonance imaging (MRI).
• Other indications for CT scan are increased intracranial pressure (before lumbar puncture) and head trauma with facial or skull fractures

Question 9

Whaat is the relevannce of X-rays in a Ct scan?

Answer 9

• X-rays pass from a rotating source around the head (or
other body part), with unabsorbed X-rays reaching a rotating detector

• After a rotation, the X-ray source and detectors are moved to a new plane, creating a new slice (tome)

• CT can differentiate bone, white matter, gray matter
and fresh blood

Question 10

What is the main use of CT scans?

Answer 10

• CT often reveals subdural hemorrhages, which often reflect trauma-induced tearing of the dura or tiny cerebral veins that traverse the dura from the subarachnoid space
• Subdural hemorrhages often assume a crescent shape

Question 11

What is basic magnetic resonance imagery?

Answer 11

• Magnetic moments of hydrogen protons aligned in strong magnetic field
• Radio waves change alignment and synchrony of spin, with protons subsequently relaxing to their prior state
• Relaxation yields signals that generate an image
• T1 signals (strong in fatty tissue) and T2 signals (strong in watery tissue) revealing distinct aspects of anatomy and pathology

Question 12

Comoare T1 and T2 weighted scans in tumor detection

Answer 12

• T1-weighted MRI, without contrast, is often poor at localizing boundaries of tumors in brain.
• A contrast agent dramatically improves the capacity of the T1-weighted MRI to reveal the boundaries of the tumor, which are associated with compromise of the blood-brain barrier.
• T2-weighted MRI poorly demonstrates tumors but can reveal inflammatory reactions in surrounding tissue.

Question 13

What are the advantages and disadvantages of the MRI?

Answer 13

• Advantages
– Excellent structural resolution
– Sensitive to edema
– No ionizing radiation
– Relatively common and accessible

• Disadvantages
– More expensive than CT
– Cannot be used when paramagnetic metals in body (watch also for cardiac pace-makers)

Question 14

What is MR angiography?

Answer 14

Contrast agent (gadolinium) is introduced to the vascular system to reveal normal and abnormal blood vessels (e.g., expressing stenoses or aneurysms)

Question 15

What is a positron emission tomography (PET)?

Answer 15

Evaluation of the distribution of radioactive isotopes by a computational method (like CT, MRI) to show metabolism (e.g., glucose) in the brain

Question 16

How does PET work?

Answer 16

• In Positron Emission Tomography (PET), 18F-deoxyglucose, a positron-emitting radio-isotope with a short half-life, is administered. Neurons take up but do not metabolize 18F-deoxyglucose. Consequently, 18F-deoxyglucose accumulates in more active neurons, which therefore emit higher numbers of positrons.
• The emitted positrons eventually collide with electrons, producing a pair of photons (gamma-rays) that move in opposite directions. The events are detected and counted by scintillation material in the scanning device. The data generate an image that shows the metabolically active areas of the brain.

Question 17

Define Single Proton Emission Computerized Tomography (SPECT)

Answer 17

Evaluation of the distribution of radioactive isotopes by a computation method (like CT, MRI) to show perfusion in the brain

Question 18

How does SPECT work?

Answer 18

In SPECT (Single Photon Emission Computed Tomography), a patient receives an intravenous gamma-ray- emitting radiotracer, usually 99mTc or 123I. Tissues with higher perfusion accumulate more of the radiotracer, leading to locally higher gamma-ray emission. A gamma camera, rotating around the patient measures the gamma-activity and hence perfusion. The data are digitally stored to allow transformation into images. SPECT shows cerebral blood-flow.

Question 19

What is the technique of radioactive isotopes diagnosistics ?

Answer 19

• Technique:
– Injection of a radiotracer, for instance 99mTc or 123I.
– Measurement with a gamma-camera
– By computation, the position of the source of the emission is estimated

– Radiotracer (e.g., 18F-deoxyglucose – short half-life) is taken up by the neurons like glucose but not metabolized → accumulation (marker for glucose metabolism)

– In the unstable isotope, a proton decays into a neutron, remaining in the nucleus, and a positron, which travels away

Question 20

What is the indication of diagnosis with radioactive isotopes?

Answer 20

• Indication:

– Information on cerebral blood-flow

Question 21

Explain in detail the technique of radioactive isotopes

Answer 21

– Radiotracer (e.g., 18F-deoxyglucose – short half-life) is taken up by the neurons like glucose but not metabolized → accumulation (marker for glucose metabolism)

– In the unstable isotope, a proton decays into a neutron, remaining in the nucleus, and a positron, which travels away

The positron eventually collides with an electron, emitting two gamma-rays (photons) at 1800 from one another

– Detectors encircle the head and record an event if two opposite detectors receive gamma-impulse simultaneously

– By computation, the position of the source of the emission is estimated

Question 22

What are the disadvantages of radioactive isotopes?

Answer 22

An on-site cyclotron ($$$$) is needed to produce the radiotracers (short half-life) used in PET unless longer half- life tracers can be used.

Question 23

What are the indications of radioactive isotopes for diagnostic purposes?

Answer 23

• Tumors
  – Epileptogenic focus
  – Brain atrophy (presenile)
  – Parkinson disease

Question 24

Why do we use DSA and CT of Angiona?

Answer 24

SPECT poorly reveals structure and vascular abnormalities