The Basics of Ultrasound, Nuclear Medicine and MRI Scans

Question 1

How are ultrasound images created?

Answer 1

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

Question 2

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

Answer 2

Strength of echo

Question 3

What produces an acoustic shadow?

Answer 3

Almost 100% of sound reflected

Question 4

Where is ultrasound not very useful?

Answer 4

Brain
Lung
Areas behind bowel gas

Question 5

What is the convention for displaying sagittal sections in ultrasound?

Answer 5

Patient’s head on left of image

Question 6

What is the convention of displaying transverse sections in ultrasound?

Answer 6

Patient’s right side on left of image

Question 7

What is the intensity of solid organs in ultrasound?

Answer 7

Mid-level - appear grey

Question 8

Define anechoic

Answer 8

Few, if any, echoes

Display is black

Question 9

Which tissues are anechoic in ultrasound?

Answer 9

Fluids

Question 10

Define echogenic

Answer 10

Bright in ultrasound

Question 11

What are acoustic shadows?

Answer 11

Bright areas causing darker echoes behind them in ultrasound

Question 12

What is posterior enhancement?

Answer 12

Dark areas causing brighter echoes behind them in ultrasound

Question 13

What is Doppler ultrasound?

Answer 13

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

Question 14

How can a Doppler ultrasound be displayed?

Answer 14

Colour

Velocity waveform

Question 15

What can a Doppler ultrasound do?

Answer 15

Detect blood flow
Determine direction of flow
Detect stenoses

Question 16

Where is contrast enhanced ultrasound (CEUS) used?

Answer 16

Cardiac
Liver
Renal

Question 17

What is the contrast used in CEUS?

Answer 17

Microbubbles injected intravenously

Dramatically enhance signal

Question 18

Is CEUS safe?

Answer 18

Yes, very safe

Can be used in presence of renal failure

Question 19

What are whiter images in ultrasound called?

Answer 19

Hyperechoic

More echogenic

Question 20

What are darker images in ultrasound called?

Answer 20

Hypoechoic

Less echogenic

Question 21

What are the advantages of ultrasound?

Answer 21

No radiation
Real time
Portable
Non-invasive
Relatively cheap

Question 22

What are the disadvantages of ultrasound?

Answer 22

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

Question 23

What are the clinical applications of ultrasound?

Answer 23

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

Question 24

What are the two types of nuclear medicine?

Answer 24

Diagnostic = imaging that makes use of radioisotopes
Therapeutic = therapy using radioisotopes

Question 25

How does radioisotope imaging work?

Answer 25

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

Question 26

What is a radiopharmaceutical?

Answer 26

Radioisotope tagged to an agent that will target organ of interest

Question 27

What is the most common gamma ray emitter used?

Answer 27

Technetium 99-m

Question 28

Define hot spot

Answer 28

Focal area of increased isotope uptake in nuclear medicine | Generally displayed as darker

Question 29

Define cold spot

Answer 29

Focal area of decreased isotope uptake in nuclear uptake

Question 30

Define photopaenia

Answer 30

Relative decrease in isotope uptake

Question 31

Define FDG avid

Answer 31

Greater FDG uptake and retention in PET | Appears as darker area

Question 32

How are ventilation perfusion scans performed in nuclear medicine?

Answer 32

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

Question 33

What is radioisotope biliary imaging most often used for?

Answer 33

Assessing gall bladder pathology

Question 34

What agent is mostly used in PET studies?

Answer 34

18F-fluorodeoxyglucose (FDG) | Uptake reflects metabolic activity

Question 35

What are FDG PET studies used for?

Answer 35

Tumour detection | - Powerful staging modality

Question 36

Other than tumours, what else takes up FDG?

Answer 36

Normal tissues, especially - Brain - Myocardium Inflammatory tissue

Question 37

How is excellent spatial resolution created in PET studies?

Answer 37

Combined with CT

Question 38

What are the advantages of diagnostic nuclear medicine?

Answer 38

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

Question 39

What are the disadvantages of diagnostic nuclear medicine?

Answer 39

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

Question 40

How does MRI work?

Answer 40

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

Question 41

What are the clinical applications of MRI?

Answer 41

``` 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 ```

Question 42

What are T1 weighted sequences?

Answer 42

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

Question 43

What are T2 weighted sequences?

Answer 43

Fluid sensitive Demonstrate pathology as bright Stationary fluid as bright

Question 44

What are brighter areas in MRI called?

Answer 44

High signal | Hyperintense

Question 45

What are darker areas in MRI called?

Answer 45

Low signal | Hypointense

Question 46

Define isointense

Answer 46

Tissue that's same intensity as surrounding tissue

Question 47

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

Answer 47

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

Question 48

What are contrast enhanced scans in MRI?

Answer 48

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

Question 49

What is diffusion weighted imaging (DWI) in MRI?

Answer 49

Shows freedom of water molecule motion | Areas of diffusion restriction = high signal

Question 50

What are MR angiograms and venograms?

Answer 50

Images of flow within blood vessels

Question 51

What is MR cholangio-pancreatography (MRCP)?

Answer 51

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

Question 52

What are the contraindications to MRI?

Answer 52

``` 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 ```

Question 53

What are the contraindications to contrast administration in MRI?

Answer 53

Significant renal impairment because of risk of developing nephrogenic systemic fibrosis

Question 54

What are the advantages of MRI?

Answer 54

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

Question 55

What are the disadvantages of MRI?

Answer 55

Cost Extended duration of exam Less widely available than CT Claustrophobia