• Shuffle
    Toggle On
    Toggle Off
  • Alphabetize
    Toggle On
    Toggle Off
  • Front First
    Toggle On
    Toggle Off
  • Both Sides
    Toggle On
    Toggle Off
  • Read
    Toggle On
    Toggle Off
Reading...
Front

Card Range To Study

through

image

Play button

image

Play button

image

Progress

1/58

Click to flip

Use LEFT and RIGHT arrow keys to navigate between flashcards;

Use UP and DOWN arrow keys to flip the card;

H to show hint;

A reads text to speech;

58 Cards in this Set

  • Front
  • Back

Five advantages of MRI vs CT?

1. Better contrast resolution than CT


2. No radiation


3. Highly sensitive for acute infarcts


4. Fewer allergic reactions than CT


5. MRA and MRV can be nonctrast

Disadvantages of MRI vs CT? (7)

1. Less spatial resolution than CT


2. High cost


3. Less availability


4. Nephrogenic systemic fibrosis with poor renal function


5. Claustrophobia


6. Contraindicated devices (some pacers)


7. No use of gadolinium in pregnant patients

What is the basis for contrast resolution of soft-tissue in MRI scans?

Protons vary in density in different tissues

What is T1/T2?

Time constant

What does T1 measure?

T1 describes the time required for protons in a specific tissue to recover back to thermal equilibrium after RF excitation stops. T1 equals the time when 63% of the magnetization has recovered its original alignment with the scanner's main magnetic field. T1 is unique for every tissue and is a measure of how quickly a tissue can be magnetized.

What does T2 measure?

Transverse relaxation. After the RF energy stops, the proton spins lose synchronization, becoming dephased. Dephasing causes the measurable signal to decay, and T2 equals the time after excitation when 63% of the signal is lost (i.e., a measure of how quickly a tissue can lose its magnetization)

What is time of repetition?

Time between each RF pulse (time protons are allowed to align)

What is time of echo?

Time provided for energy to be released or detected after the RF pulse stops

T1-weighted sequences demonstrate what well? When are they used?

Anatomy; primary sequence used for comparison of pre-gadolinium and post-gadolinium enhancement

T2-weighted sequences are useful when?

Demonstrating inflammation, edema, and fluid, which in most cases renders pathologic processes more conspicuous

Lesions that restrict diffusion? (6)

1. Acute infarction (up to 10 to 14 days)


2. Highly cellular tumors (lymphoma, meningioma, PNETs)


3. Pyogenic abscesses (restrict centrally)


4. Cholesteatomas


5. Mucinous adenocarcinomas


6. Epidermoids

Relationship among time of repetition (TR), time of echo (TE), and T1?

Short TR, short TE (TR <500ms, TE <20ms)

Relationship among time of repetition (TR), time of echo (TE), and T2?

Long TR, long TE (TR >2,000 ms, TE >70 ms)

Relationship among time of repetition (TR), time of echo (TE), and proton density?

Long TR, short TE (TR >2,000-3,000, TE 25-30 ms)

Effect of gadolinium on T1 and T2?

Shortens both, T1 more than T2

T1 brightness is due to T1 shortening. What may cause that shortening? (7)

1. Subacute blood products


2. Fat (myelin)


3. Proteinaceous material


4. Slow flow


5. Melanin


6. Hydrated calcium


7. Gadolinium

T1 darkness is due to T1 prolongation. What may cause that shortening? (5)

1. CSF


2. Edema


3. Nonhydrated calcium


4. Air


5. Most tumors

T2 brightness is due to T2 prolongation. What may cause that prolongation? (3)

1. CSF


2. Edema


3. Most tumors

T2 darkness is due to T2 shortening. What may cause that shortening? (5)

1. Bone


2. Hemosiderin


3. Ferritin


4. Mucinous material


5. Air

Additional MRI sequences (apart from T1 and T2) that may be used? (6)

1. Fluid-attenuation inversion-recovery sequences - suppress build fluid signal (as in ventricles, cisterns, or ocular vitreous) and thus render pathologic areas more conpicuous, especially SAH


2. Short-tau inversion-recovery sequence - useful for highlighting fluid or edema, more sensitive than T2 in the spine (myelopathies)


3. Diffusion-weighted imaging (DWI) - provide unique information based on microscopic motion of water


4. Perfusion-weighted imaging


5. Gradient-recalled echo or susceptibility-weighted imaging sequences


6. Post-gadolinium (contrast) multiplanar or 3D volume T1-weighted images

What is T2 shine through?

If a lesion appears bright on the DWI and either bright or isointense to the surrounding tissue on apparent diffusion coefficient images, there is no restriction of diffusion

How can you differentiate cytotoxic edema (infarct) from vasogenic edema?

DWI

Important note about gadolinium (time of flight) MRA?

Direction-dependent; thus, if a vertebral artery appears absent on the time-of-flight image but present on the gadolinium bolus image, retrograde flow in this vessel is implied, most likely from a subclavian steal phenomenon

Functional MRI principle?

As blood flow increases to more metabolically active areas in the brain, the ratio of oxyhemoglobin in those areas increases, resulting in a measurable difference (increase) in T2

When would MR spectroscopy be useful? (4)

1. To identify a lactate doublet in patients with mitochondrial cytopathies


2. Creatine deficiencies


3. Canavan disease in pediatric patients


4. Tumor characterization

Sagittal MRI images of the spine provide excellent coverage for what?

The spinal canal

Axial MRI images are most helpful for?

Discerning whether a process is intradural or extradural

Enhancements in primary brain tumors correlates with what?

Higher histologic grade; this relationship does not hold true for spine tumors

In patients who've had lumbar spine surgery, use of gadolinium can be useful for what?

Differentiating postoperative granulation tissue from disk material because granulation tissue enhances but disk material enhances minimally and only peripherally

Differential diagnosis of spine lesions based on location: extradural (7)

1. Meningioma


2. Metastases (and lymphoma)


3. Hematoma


4. Abscess


5. Nerve sheath tumor


6. Disk bulge or fragment


7. Synovial or meningeal cyst

Differential diagnosis of spine lesions based on location: intradural, extramedullary (5)

1. Meningioma


2. Metastases (and lymphoma)


3. Hematoma


4. Abscess


5. Nerve sheath tumor

Differential diagnosis of spine lesions based on location: indradural, intramedullary (7)

1. Ependymoma (if well defined)


2. Astrocytoma (if ill defined)


3. Hemangioblastoma (enhances)


4. Myelitis


5. Infarct


6. Dural arteriovenous fistula (flow voids)


7. Metastases (and lymphoma)

How are CT images generated?

According to a tissue's density, i.e., ability to stop photons; uses x-ray images and filtered back projection to provide 2D and isometric voxel 3D images with better spatial resolution than MRI

Acute hemorrhage will show up how on CT? Subacute? Chronic?

Hyperdense; subacute hemorrhage becomes more isodense, and chronic blood products are hypodense

What is pseudoarachnoid hemorrhage?

Marked cerebral edema that causes the basal cisterns to appear relatively hyperdense, thereby mimicking the typical CT appearance of subarachnoid hemorrhage

Typical Hounsfield units of acute venous sinus thromboses in the first 1 to 2 days?

70 or more; CT attenuation correlates directly with the hematocrit value; thus, arterial and venous density will be higher in young patients

CT perfusion is becoming more widely available. What is it useful for?

CT perfusion provides maps of relative cerebral blood volume, blood flow, mean transit time, and time to peak. Mismatch between relative cerebral blood volume and relative cerebral blood flow indicates that there may be salvageable brain tissue

CT perfusion provides maps of relative cerebral blood volume, blood flow, mean transit time, and time to peak. Mismatch between relative cerebral blood volume and relative cerebral blood flow indicates that there may be salvageable brain tissue

Relative density of water on CT?

0 Hounsfield units

Relative density of bone on CT?

+400-1,000 H units

Relative density of soft tissue on CT?

40-80 H units

Relative density of fat on CT?

-60-80 H units

Relative density of air on CT?

-1,000 H units

Relative density of blood on CT?

40-90 H units ( acute = bright, chronic = dark)

Disadvantages of CT? (4)

1. Radiation


2. Iodine allergy


3. Iodine: may impair renal function


4. Contrast resolution is inferior to MRI

Advantages of CT? (5)

1. CT/CTA/CTV is widely available


2. Very rapid image acquisition


3 .Claustrophobia is basically not an issue


4. Less expensive than MRI


5. Better spatial resolution than MRI

Epidural hematomas on CT?

Do not cross suture lines unless there is an associated fracture, but they can cross the midline. This feature is more reliable diagnostically than relying on the lenticular shape that can be seen with other types of hematomas

Subdural hematomas on CT?

Cross suture lines and may appear acute, subacute, or chronic

Subarachnoid hemorrhage on CT?

Fills the subarachnoid space and cisterns

When would single-photon emission CT be of use?

1. Demonstrating cerebral perfusion, assessing brain death or seizure foci


2. Assess vasodilatory reserve in patients with a fixed stenosis or when an artery may need to be sacrificed during surgery

When would positron emission tomography (PET) be of good use?

1. Discerning metastases or the primary lesion in a paraneoplastic disorder

2. Evaluation of dementia


3. Evaluation of epilepsy


4. Evaluation of traumatic brain injury

When would FDG-PET be of good use?

Cerebral PET visualizes hypometabolic regions, such as those found in neurodegenerative conditions, quite well. Typical patterns suggest the clinical diagnosis, such as Alzheimer or Lewy Body dementia

Where would lesions most commonly be seen in Alzheimer disease on FDG-PET?

Temporoparietal

Where would lesions most commonly be seen in frontotemporal dementia on FDG-PET?

Frontodemporal

Where would lesions most commonly be seen in Lewy Body dementia on FDG-PET?

Temporoparietal and occipital

CT findings in hyperacute ischemic cerebral infarction?

Normal or minimal blurring of gray-white junction

CT findings in acute ischemic cerebral infarction?

1. Indistinct gray-white junction


2. Poorly defined hypodensity


3. Edema

CT findings in subacute ischemic cerebral infarction?

Hypodensity with temporal evolution toward more circumscribed focus

CT findings in chronic ischemic cerebral infarction?

1. Well circumscribed


2. Low attenuation