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Questions and Answers
What is one of the main indications for Magnetic Resonance Angiography (MRA)?
Which technique in Magnetic Resonance Angiography utilizes radiofrequency pulses to saturate stationary tissue?
Which of the following statements about Maximum Intensity Projection (MIP) is true?
What is a primary contraindication for Computed Tomography Angiography (CTA)?
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Which of the following methods allows for the quantification of blood flow velocity in Magnetic Resonance Angiography?
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What is the primary method used in plain radiography to produce images?
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Which of the following best describes a contraindication for using plain radiography?
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In computed tomography (CT), how are images created?
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What enhances soft-tissue details in CT imaging?
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What is a distinct advantage of helical CT over conventional CT scanning?
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Which of the following is NOT an indication for using CT imaging?
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What is the significance of the HU value in CT imaging?
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What type of tissues appears brightest on a CT scan?
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What does T1 relaxation time primarily describe?
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Which imaging technique is primarily better for demonstrating normal anatomy?
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In T2-weighted images, which of the following tissues appears hyperintense?
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What is the main effect of Gadolinium as an MRI contrast medium?
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Which of the following accurately characterizes the T2 relaxation process?
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Which statement correctly describes the TR and TE parameter requirements for T1-weighted imaging?
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What characterizes proton weighted imaging?
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Which of the following is a potential risk associated with the use of Gadolinium in MRI?
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What feature makes diffusion-weighted imaging (DWI) ideal for detecting recent infarctions?
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Which of the following is NOT a contraindication for MRI?
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What complication is NOT associated with catheter angiography?
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Which imaging technique involves injecting contrast material into a peripheral vein?
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Which condition would most likely NOT be evaluated using MRI?
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What is a common reason for choosing digital subtraction angiography (DSA) over other imaging techniques?
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What type of imaging involves the use of high-speed spiral CT scanning to capture detailed vascular images?
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Which of the following conditions is most likely to prompt an MRI examination?
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What is the primary advantage of using MRI over CT for imaging studies?
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In which scenario would a CT scan be preferred over an MRI?
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What should be verified when reviewing imaging studies?
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If imaging studies show no abnormality, what should a clinician do next?
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What is essential when imaging of the orbit and head is performed?
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Which imaging modality is particularly indicated for vascular disease evaluation?
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What is a key consideration when selecting a scan for imaging studies?
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What should be done if the imaging findings do not match clinical findings?
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Study Notes
Neuroimaging in Neuro-Ophthalmic Disease
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Plain Radiography uses X-rays to create 2-dimensional images of the body by measuring how much radiation is absorbed by different tissues.
- Contraindication: Pregnancy
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Computed Tomography (CT Scan) uses X-rays to create cross-sectional images of the body.
- Different tissue densities have different attenuation coefficients, which are measured and used to reconstruct the image.
- Darker areas on the CT scan represent less dense tissues (e.g., air).
- Brighter areas on the CT scan represent denser tissues (e.g., bone).
- Contrast material (iodinated) can be used to enhance the visibility of soft tissues.
- Helical CT uses a continuous rotating X-ray source and detector to obtain a 3-dimensional data set.
- Multidetector CT (MDCT) uses multiple detectors to acquire data more quickly.
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Indications for CT:
- Complex fractures
- Foreign body localization
- Orbital lesions (e.g., hamartomas, choroidal osteoma)
- Lesions causing bone loss or calcification
- Acute hemorrhagic lesions (e.g., subarachnoid or intraparenchymal hemorrhage)
- Thyroid eye disease (especially before orbital surgery)
- Patients with MRI contraindications (e.g., claustrophobia)
- Risk: Ionizing radiation
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Magnetic Resonance Imaging (MRI) uses magnetic fields and radio waves to create detailed images of the body.
- T1 Relaxation (spin-lattice relaxation) describes how quickly longitudinal magnetization recovers.
- T2 Relaxation (spin-spin relaxation) describes how quickly transversal magnetization vanishes.
- T1-weighted images (T1WI) demonstrate differences in T1 relaxation times of tissues.
- T2-weighted images (T2WI) demonstrate differences in T2 relaxation times of tissues.
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T1:
- Cerebrospinal fluid (CSF) and vitreous humor are hypointense (dark).
- Gray matter is relatively hypointense compared to white matter.
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T2:
- CSF and vitreous humor are hyperintense (bright).
- Gray matter is relatively hyperintense compared to white matter.
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Imaging Terms:
- TR (Repetition Time): The time between successive radiofrequency (RF) pulses.
- TE (Echo Time): The time interval between the beginning of transverse relaxation and when the magnetization is measured to produce image contrast.
- T1 Weighted: Short TR/TE
- T2 Weighted: Long TR/TE
- Proton Weighted: Long TR with short TE (signal related to proton density)
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Gadolinium is a paramagnetic substance used as an MR contrast medium:
- It enhances local magnetic field and increases signal intensity, making it useful for identifying recent infarctions.
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Contraindications:
- May cause nephrogenic systemic fibrosis.
- Contraindicated in patients with a history of previous gadolinium allergy.
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Indications for MRI:
- Optic disc edema or pallor
- Optic neuritis
- Orbital mass, thyroid-associated orbitopathy, orbital injury, orbital inflammation, asymmetry, exophthalmos, enophthalmos
- Vision loss (optic nerve, pre-chiasm, chiasm, or post-chiasm symptoms).
- Diplopia disorders of neural origin or ophthalmoplegia
- Third, fourth, sixth nerve palsy or cavernous sinus syndrome
- Nystagmus
- Facial or lid disorders with neural origin (e.g., brainstem)
- Acquired Horner's syndrome
- Headache or eye pain of neuro-ophthalmic causes
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Contraindications for MRI:
- Incompatible medical implants/foreign bodies:
- Cardiac pacemakers
- Metallic prosthetic devices
- Intracranial metal vascular clips
- Old cardiac valve prosthesis
- Cochlear implants or neuro-stimulators
- Metallic objects on patients (e.g., necklaces, rings, watches, eye makeup)
- Pregnancy
- Incompatible medical implants/foreign bodies:
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Intracranial Vascular Imaging:
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Catheter Angiography (DSA) is an invasive procedure that uses X-rays and iodinated contrast material to visualize blood vessels.
- Provides details about the anatomy and function of the blood vessels.
- Can be used for diagnosis and treatment (e.g., stenting).
- Complications:
- Contrast media reactions
- Hematoma at puncture site
- Vasospasm
- Emboli leading to ischemia
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Catheter Angiography (DSA) is an invasive procedure that uses X-rays and iodinated contrast material to visualize blood vessels.
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Computed Tomography Angiography (CTA):
- Uses X-rays and iodinated contrast material injected intravenously to obtain detailed images of blood vessels.
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Advantages:
- Noninvasive
- Faster than traditional angiography
- Provides 3-dimensional images
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Contraindications:
- Pregnancy
- Severe iodinated contrast allergy
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Magnetic Resonance Angiography (MRA):
- Noninvasive and does not use ionizing radiation or contrast material.
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Types of MRA Techniques:
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Time of Flight (TOF):
- Fresh inflowing blood produces a high initial magnetization signal.
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Phase Contrast (PC):
- Uses magnetic gradients to induce phase shifts in flowing blood, allowing for flow velocity and rate quantification.
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Contrast-enhanced MRA:
- Involves intravenous injection of gadolinium-based contrast medium.
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Time of Flight (TOF):
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Indications:
- Evaluation of aneurysms, vascular malformations, dissection, stenosis, occlusion
- Transient ischemic attacks
- Amaurosis fugax
- Completed strokes
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Magnetic Resonance Venography (MRV):
- Noninvasive, uses MRI to visualize veins.
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Indications:
- Patients with venous diseases (e.g., deep vein thrombosis)
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Choosing the Right Imaging:
- In general, MRI is preferred for visualizing soft tissues and visual pathways.
- CT is indicated for trauma, acute hemorrhage, fractures, or calcifications within a mass lesion and MRI contraindications.
- For suspected vascular disease, consider MRA, CTA, and CA (catheter angiography).
- Orbital imaging is often necessary in addition to brain imaging studies.
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Reviewing Imaging Studies:
- Verify patient, date, and study requested.
- Assess scan quality, orientation, and scan thickness.
- Identify normal reference structures and abnormal findings.
- Make a differential diagnosis based on scan results and correlate with clinical findings.
- Re-examine the clinical findings and imaging study if the findings do not match.
- Recognize that the lack of an imaging abnormality does not exclude pathology.
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