What is plain film analysis used to evaluate? What does it detect?
structures of the skull, facial bones, and sinus Fractures; abnormal calcifications; developmental abnormalities; osteolytic disorders; osteoblastic disorders
CT & MRI imaging planes?
the horizontal (axial), coronal, and sagittal planes used to describe basic neuroanatomy
Sometimes the axial slices in CT scans are adjusted a few degrees off of the true axial plane. Why? (2 reasons)
-Enables the whole brain to be covered using fewer slices. -This procedure reduces radiation exposure to the eyes.
MRI axial slices are true horizontal slices: True or False
CT scans differ in what two ways from conventional X–rays?
1) Rather than taking only one view, the CT X–ray beam is rotated around the patient and takes many different views 2) The CT X–ray data are reconstructed by a computer to obtain a detailed image of all the structures in the slice (e.g., liquid, air, bone, soft tissue)
Four facts about the single-slice CT
1) the scanner is shaped like a large ring; 2) the patient lies on the table & moves through the ring in small steps; 3) at each stop, X–rays are scanned through the patient and picked up by detectors on the opposite side of the ring; 4) the amount of energy absorbed depends on the density of the tissues traversed
On a CT scan, what does white represent?
dense structures, like bone
On a CT scan, what does black represent?
less dense materials, like air
On a CT scan, what does hyperdense refer to?
On a CT scan, what does hypodense refer to?
On a CT scan, what does isodense refer to?
intermediate density materials similar to brain tissue
On a CT scan, what shade is CSF?
On a CT scan, what color is fat tissue just outside the skull (subcutaneous)?
On a CT scan, what color is white matter?
Slightly darker than celluar gray matter due to its high myelin content (gray matter is slighly lighter than white matter due to its high water content)
Density in CT scans is often expressed in what unit?
Hounsfield units (HU) Water = 0 HU Air = –1000 HU
What do hemorrhages look like on a CT scan?
It depends on how old the hemorrhage is: Fresh intracranial hemorrhage shows up as a hyperdense area relative to brain tissue. One-week old hemorrhage looks isodense. Older hemorrhage (2-3 weeks) looks hypodense.
Are acute cerebral infarcts readily detectable on CT scans?
No, acute infarcts (the first 6–12 hours) are often not seen on CT scans. After 12 hours, cell death and edema lead to an area of hypodensity seen in the distribution of the occluded artery.
What does the cerebral infarct look like when it's weeks to months old on a CT scan?
The brain tissue surrounding the infarct may shrink, producing a local area of prominent sulci or enlarged ventricles. Persistent areas of hypodensity may be the result of gliosis and brain necrosis with replacement by CSF.
What do neoplasms look like on a CT scan?
They may be hypodense, hyperdense, or isodense, depending on the type or stage.
What is helpful for visualizing neoplasms on a CT scan?
IV contrast dye
How do you detect mass effect on a CT scan?
Look for localized compression of ventricles, effacement of sulci, or distortions in other brain structures (e.g., herniations)
How does IV contrast work in CT scans?
The contrast material contains iodine which is denser than brain and will therefore appear hyperdense in areas of increased vasularity or breakdown of the blood–brain barrier. Often, images are obtained with and without contrast for comparison.
What is one caveat regarding intracaranial hemorrhage and CT contrast?
Small hemorrhages often appear as whitish areas at the base of the brain on CT scan. These areas could be masked by the normal hyperdense contrast material. In suspected intracranial hemorrhage, it is very important to obtain a NON-CONTRAST CT scan.
What is myelography?
A combination of CT scan with a procedure in contrast dye is injected into the CSF via a needle. This allows a better visual of nerve roots and impingements on the spinal CSF space.
For a head trauma, which is better, CT or MRI?
For a subtle tumor or infarct, which is better, CT or MRI?
For a brainstem lesion, which is better, CT or MRI?
For a fresh hemorrhage, which is better, CT or MRI?
For an old hemorrhage, which is better, CT or MRI?
When speed is needed, which is better, CT or MRI?
When there is a skull fracture, which is better, CT or MRI?
When a person has a pacemaker, which is better, CT or MRI?
When assessing low–contrast or small lesions such as MS plaques or low–grade astrocytomas, which is better, CT or MRI?
What happens during an MRI?
A poweful magnetic field is applied that causes protons in the person to align their intrinsic spins in parallel with the magnetic field.
Which protons are the ones relevant to conventional MRI?
those protons forming hydrogen nuclei
What is the benefit of using either T1–weighted versus T2–weighted MRI?
T1– looks like an anatomical brain section; it is better for identifying anatomy because the resolution is better. T2– looks like a film negative; it is better for detecting pathological changes because while the resolution is poor, the contrast is good
What are two factors that affect the intensity of MRI images/signals?
1) the amount of hydrogen protons 2) Metallic implants can distort images
Intracranial hemorrhage on MRI: What is the characteristic course?
Acute hemorrhage is hard to see b/c it is gray and looks like CSF. Subacute hemorrhage looks white. Chronic hemorrhage looks dark. They also usually have a bright center with a dark rim.
The study of the central nervous blood vessels and related vasculature using radiographs during injection of a intravascular contrast medium. It is the gold standard for evaluating vasular diseases in the head, neck, & spine.
Before the advent of MRI & CT, what was neuroangiography was used to detect?
Slight distortions in the patterns of blood vessels suggestive of intracranial mass lesions
What are the current uses of neuroangiography?
1) visualize lesions of blood vessels 2) assess the vascular anatomoy of tumors when planning neurosurgery
What factors make angiography an invasive procedure?
It requires local anesthesia and catheter insertion, typically in the femoral artery
What are less-invasive techniques for visualizing blood vessels? (3)
1) Doppler ultrasound 2) Magnetic Resonance Angiography (MRA) 3) Spiral CT Angiography (CTA) These techniques are not as sensitive or specific
It is the original method for measuring brain activity and is useful in evaluating for seizure activity and in detecting widespread abnormality in brain function.
Is an EEG good at detecting focal brain lesions?
No. Its sensitivity and spatial resolution for detecting focal brain lesions is poor.
It is similar to an EEG. The brain's electrical activity is recorded in response to specific stimuli.
What is unique about imaging techniques like PET, SPECT, fMRI compared to CT, MRI?
These techniques produce images based on blood flow or dynamic blood flow volume (i.e., metabolic activity)" Positron Emission Tomography (PET); Single photon emission computerized tomography (SPECT) Dynamic contrast functional MRI (perfusion MRI) Blood oxygen level dependent functional MRI (BOLD fMRI) Magnetic Resonance Spectroscopy (MRS) Xenon regional cerebral blood flow mapping (Xe rCBF)
What neuroimaging technique based on metabolic activity is particularly useful in evaluating brain tumors? Why?
PET scans: high grade neoplasms demonstrate increased metabolism while low grade neoplasms demonstrate decreased activity.
Which technique can detect early areas of ischemia long before conventional MRI imaging?
What does Ictal–Interictal SPECT Difference Imaging look like between seizures?
It shows decreased regional cerebral blood flow between seizures.
What does Ictal–Interictal SPECT Difference Imaging look like ictally?
It shows increased regional cerebral blood flow ictally.