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MD2 Foundation > The Basics of Ultrasound, Nuclear Medicine and MRI Scans > Flashcards

The Basics of Ultrasound, Nuclear Medicine and MRI Scans Flashcards

1
Q

How are ultrasound images created?

A

This sectional images using echoes returned from tissue interfaces
Position of echo display derived from known speed of sound
Strength of echo determined by difference in tissues acoustic impedance

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2
Q

What determines the brightness of display on the monitor in ultrasound?

A

Strength of echo

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3
Q

What produces an acoustic shadow?

A

Almost 100% of sound reflected

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4
Q

Where is ultrasound not very useful?

A

Brain
Lung
Areas behind bowel gas

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5
Q

What is the convention for displaying sagittal sections in ultrasound?

A

Patient’s head on left of image

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6
Q

What is the convention of displaying transverse sections in ultrasound?

A

Patient’s right side on left of image

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7
Q

What is the intensity of solid organs in ultrasound?

A

Mid-level - appear grey

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8
Q

Define anechoic

A

Few, if any, echoes

Display is black

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9
Q

Which tissues are anechoic in ultrasound?

A

Fluids

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10
Q

Define echogenic

A

Bright in ultrasound

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11
Q

What are acoustic shadows?

A

Bright areas causing darker echoes behind them in ultrasound

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12
Q

What is posterior enhancement?

A

Dark areas causing brighter echoes behind them in ultrasound

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13
Q

What is Doppler ultrasound?

A

Weak echoes that return from moving blood have slightly different frequency to transmitted ultrasound
Amount and direction of frequency change depends on velocity and direction of blood flow

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14
Q

How can a Doppler ultrasound be displayed?

A

Colour

Velocity waveform

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15
Q

What can a Doppler ultrasound do?

A

Detect blood flow
Determine direction of flow
Detect stenoses

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16
Q

Where is contrast enhanced ultrasound (CEUS) used?

A

Cardiac
Liver
Renal

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17
Q

What is the contrast used in CEUS?

A

Microbubbles injected intravenously

Dramatically enhance signal

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18
Q

Is CEUS safe?

A

Yes, very safe

Can be used in presence of renal failure

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19
Q

What are whiter images in ultrasound called?

A

Hyperechoic

More echogenic

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20
Q

What are darker images in ultrasound called?

A

Hypoechoic

Less echogenic

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21
Q

What are the advantages of ultrasound?

A 
No radiation
Real time
Portable
Non-invasive
Relatively cheap
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22
Q

What are the disadvantages of ultrasound?

A 
Operator dependent
Limited field of view
Blind spots
Obesity
- Problem mainly for abdominal and pelvic imaging
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23
Q

What are the clinical applications of ultrasound?

A 
Obstetrics and gynaecology
Abdominal
Cardiac
Vascular
Musculoskeletal
Small parts
Interventional/intraoperative
24
Q

What are the two types of nuclear medicine?

A 
Diagnostic = imaging that makes use of radioisotopes
Therapeutic = therapy using radioisotopes
25
Q

How does radioisotope imaging work?

A

Attached to particular molecules
Introduced into body
Emit gamma rays
Gamma rays recorded by gamma camera

26
Q

What is a radiopharmaceutical?

A

Radioisotope tagged to an agent that will target organ of interest

27
Q

What is the most common gamma ray emitter used?

A

Technetium 99-m

28
Q

Define hot spot

A

Focal area of increased isotope uptake in nuclear medicine

Generally displayed as darker

29
Q

Define cold spot

A

Focal area of decreased isotope uptake in nuclear uptake

30
Q

Define photopaenia

A

Relative decrease in isotope uptake

31
Q

Define FDG avid

A

Greater FDG uptake and retention in PET

Appears as darker area

32
Q

How are ventilation perfusion scans performed in nuclear medicine?

A

2 different agents given
- 1 inhaled
- 1 IV
Mismatch used as sign of pulmonary embolism

33
Q

What is radioisotope biliary imaging most often used for?

A

Assessing gall bladder pathology

34
Q

What agent is mostly used in PET studies?

A

18F-fluorodeoxyglucose (FDG)

Uptake reflects metabolic activity

35
Q

What are FDG PET studies used for?

A

Tumour detection

- Powerful staging modality

36
Q

Other than tumours, what else takes up FDG?

A

Normal tissues, especially
- Brain
- Myocardium
Inflammatory tissue

37
Q

How is excellent spatial resolution created in PET studies?

A

Combined with CT

38
Q

What are the advantages of diagnostic nuclear medicine?

A

Can demonstrate metabolic activity and function to much greater extent than other modalities
Sensitive in detection of many forms of malignant tumours

39
Q

What are the disadvantages of diagnostic nuclear medicine?

A 
Ionising radiation
Relatively expensive
Poor anatomical resolution
- Overcome by combining with CT
Some studies lengthy
Can't guide invasive procedures
40
Q

How does MRI work?

A

Patient placed in very strong magnetic field
H atom acts like magnet - aligns itself along direction of magnetic filed
Radiofrequency signal applied > protons excited > change alignment
Radiofrequency signal stopped > protons return to initial alignment = relaxation
Radiofrequency signal emitted - used to create image

41
Q

What are the clinical applications of MRI?

A 
Most common
- CNS
- Musculoskeletal
Tumour detection
- Liver
- Pancreas
Bile ducts
- Bile duct stones
- Other causes of bile duct obstruction
Small bowel imaging
- Especially in Crohn's disease
42
Q

What are T1 weighted sequences?

A

Provide anatomical resolution
Display stationary fluid as dark
Pathology tends to be dark

43
Q

What are T2 weighted sequences?

A

Fluid sensitive
Demonstrate pathology as bright
Stationary fluid as bright

44
Q

What are brighter areas in MRI called?

A

High signal

Hyperintense

45
Q

What are darker areas in MRI called?

A

Low signal

Hypointense

46
Q

Define isointense

A

Tissue that’s same intensity as surrounding tissue

47
Q

What are fluid attenuatin inversion recovery (FLAIR) sequences in MRI?

A

Useful for CNS imaging
Null CSF signal - looks black
Pathology bright

48
Q

What are contrast enhanced scans in MRI?

A 
Contain gadolinium
Alters relaxation properties of tissues
Used usually in combination with T1 sequences
Contrast enhancement appears bright
- Highlights pathology
49
Q

What is diffusion weighted imaging (DWI) in MRI?

A

Shows freedom of water molecule motion

Areas of diffusion restriction = high signal

50
Q

What are MR angiograms and venograms?

A

Images of flow within blood vessels

51
Q

What is MR cholangio-pancreatography (MRCP)?

A

Allows imaging of biliary system and pancreatic ducts without administration of contrast
Stationary fluid shows up as very bright

52
Q

What are the contraindications to MRI?

A 
Non-MRI compatible pacemakers
Intracranial aneurysm clips
Cochlear implants
Endovascular stents
Shrapnel/metallic foreign bodies
Claustrophobia
- Relative contraindication
- May need sedation
Patient size - may not fit scanner
53
Q

What are the contraindications to contrast administration in MRI?

A

Significant renal impairment because of risk of developing nephrogenic systemic fibrosis

54
Q

What are the advantages of MRI?

A

No ionising radiation
High spatial resolution
Superior soft tissue contrast resolution compared to CT
Multiplanar display
Can produce angiography/venography/cholangiography without administering contrast

55
Q

What are the disadvantages of MRI?

A

Cost
Extended duration of exam
Less widely available than CT
Claustrophobia

MD2 Foundation (42 decks)

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