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Radiology Exam 2 > Lecture 13 - MRI > Flashcards

Lecture 13 - MRI Flashcards

1
Q

MRI

A

magnetic resonance imaging

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2
Q

How do MRIs work?

A

Based on protons emitting radio waves in the presence of strong magnetic fields and pulses of radiofrequency energy

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3
Q

Benefits of MRI

A

No exposure to ionizing radiation

No significant biologic effects

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4
Q

Each set of images is from a series of radiofrequency pulses and variations in the magnetic field, called…

A

Pulse Sequence

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5
Q

Describe an MRI Scanner

A

Scanners are like a larger, thicker CT scanner

Some scanners are open at the sides or are vertical, which may assist claustrophobic patients.

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6
Q

Difference between open and closed scanners

A

Open scanners may be slower and not have the same image quality as closed scanners

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7
Q

How are scanners described?

A

Scanners described by the strength of their primary magnet

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8
Q

Typical magnet strength

A

1.5 Tesla

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9
Q

How are images produced?

A

Primary magnetic field is modified by additional fields, resulting in varied magnetic field strengths or gradients – these are used to produce the images

The fields affect the spin of hydrogen protons in the patient

Radiofrequency pulses are applied to these protons which give off radio waves that are detected by receiver coils (antennas).

Output from the coils creates the images.
Gradient fields and radio pulses chosen for each set of images (pulse sequence) creates the images but also the different appearance of tissues on the images

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10
Q

Most common pulse sequences

A 
T1 or T2 spin echo
T1 or T2 fast spin echo
T1 or T2 gradient echo
FLAIR sequence
STIR sequence
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11
Q

Sequences are usually referred to as

A

T1 or T2 sequences (or T1-weighted or T2-weighted) sequences

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12
Q

called the longitudinal relaxation time and is the time it takes for the tissue to recover to its longitudinal state before the radiofrequency pulse was given

A

T1

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13
Q

the transversal relaxation time and is the time for the tissue to regain its transverse orientation before the radiofrequency pulse was given

A

T2

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14
Q

As soon as the pulse stops…

A

relaxation begins and the spinning nuclei release energy that is picked up by the receiver coil and produces an image

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15
Q

What appears dark on a T1 image?

A 
calcification
air
chronic hemorrhage
acute hemorrhage
water (edema, CSF)

Have low signal and appears dark on the image.

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16
Q

What appears bright on a T2 image?

A

Lipids
Subacute hemorrhage
Fluid containing protein will have high signal and be bright.

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17
Q

What causes tissue to have a high signal?

A

Contrast will cause tissue with the contrast to have high signal

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18
Q

What appears dark on a T2 image?

A 
fat
calcification
air
early subacute hemorrhage
chronic subacute hemorrhage
chronic hemorrhage
acute hemorrhage
high protein
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19
Q

What will appear bright on a T2 image?

A

Water - Edema, CSF

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20
Q

Why do lipid containing tissues not affect not affect high signal?

A

T1 and T2 sequences can suppress the signal from lipids so that lipid containing tissues do not affect high signal from adjacent high signal fluid or tissue

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21
Q

Most common MRI contrast

A

Gadolinium

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22
Q

How is Gadolinium administered?

A

IV

Intraarticularly

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23
Q

How does Gadolinium work?

A

Enters the blood stream, enhances organ parenchyma, and is excreted by the kidneys

Causes a brighter signal on T1-weighted images – since fat is already bright the images are usually fat-suppressed to enhance the effect of the contrast

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24
Q

What structures light up with contrast?

A

Structures that light up with contrast are vascular (tumors) and inflammation and are described as enhancing

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25
Q

Who should not receive Gadolinium?

A

Pts with renal insufficiency

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26
Q

What can patients with renal insufficiency develop after Gadolinium?

A

Patients with renal insufficiency should not receive gadolinium as they are at risk for developing nephrogenic systemic fibrosis – produces fibrosis of skin, eyes, joints, and internal organs.

Patients with preexisting renal disease, especially dialysis patients, are at greatest risk

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27
Q

What has better soft tissue resolution?

A

MRI

MRI>CT for soft tissue resolution.

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28
Q

If contrast is indicated and CT and MRI are equivalent but contrast is contraindicated, what do you use?

A

unenhanced MRI is usually better than unenhanced CT

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29
Q

What must be removed from the patient before an MRI?

A

Has very strong magnetic fields, so metal objects are removed from the patient

Surgically implanted or imbedded metal devices and objects may be a problem.

If motion of the device or object may be harmful, then MRI cannot be done – cerebral aneurysm repair clips, vascular clips, surgical staples

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30
Q

What foreign bodies can cause an issue with MRIs?

A

Foreign bodies, such as bullets, shrapnel, and metal in the eyes, are also a problem

Patients with pacemakers, defibrillators, pain stimulator implants, insulin pumps, other implantable drug infusion pumps, and cochlear implants cannot have MRIs – devices can be deactivated by magnetic field

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31
Q

MRI Safety during pregnancy

A

Limited data on safety during pregnancy – American College of Radiology says pregnant patients can undergo MRI at any stage of pregnancy if benefit outweighs the risk. Should not be performed electively early in pregnancy, and gadolinium is not recommended in pregnancy.

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32
Q

MRI safety with metal objects

A

Some may still have an MRI depending on the metals used, the shape of the objects, and the location involved.

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33
Q

Issues with MRI

A

Very expensive
May be difficult for some patients due to psychological reasons
May not be ideal modality for all cases –bone has little or no MRI signal so CT is better

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34
Q

What images can MRI provide?

A

Axial
Sagittal
Coronal

Just like CT

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35
Q

MRI is used for…

A 
Musculoskeletal
Neurologic
GI
Endocrine/Reproductive
GU
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36
Q

What does a Musculoskeletal MRI evaluate?

A 
Bone marrow
Menisci
Tendons
Muscles
Bones
Osteomyelitis
Spine
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37
Q

What is a Musculoskeletal MRI used for?

A 
Assess for meniscal tears
Ligamentous or tendon injuries
Contusions
Occult or stress fractures
Disk disease and marrow infiltration
Differentiating scarring from prior surgery from new disease
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38
Q

A musculoskeletal MRI has a __________ negative predictive value if normal.

A

High

39
Q

Neurologic MRI evaluates…

A 
Brain - especially the posterior fossa
Tumors
Infarction
Multiple Sclerosis
Peripheral nerves looking for impingement or injury.
40
Q

GI MRI evaluates…

A

Evaluates the liver – characterizes liver lesions, detects small lesions, cysts, hemangiomas, hepatocellular carcinoma, hemochromatosis, fatty infiltration

Evaluates the biliary system – MR cholangiopancreatography for strictures, ductal dilatation

Evaluates the small and large bowel – MR enterography, appendicitis in pregnancy

41
Q

MRI Liver evaluation includes

A 
Characterizes liver lesions
Detects small lesions
Cysts
Hemangiomas
Hepatocellular carcinoma
Hemochromatosis
Fatty infiltration
42
Q

MRI Biliary system evaluation includes.

A

MR cholangiopancreatography for strictures

Ductal dilatation

43
Q

MRI evaluation of the small and large bowel:

A

MR enterography

Appendicitis in pregnancy

44
Q

MRI Endocrine/Reproductive evaluation includes:

A

Evaluates the adrenal glands – adenomas, adrenal hemorrhage

Evaluates the male pelvis – staging of rectal, bladder, and prostate carcinoma

45
Q

MRI of the GU evaluates

A

Renal Masses

Cysts vs Masses

46
Q

How does Ultrasound work?

A

High frequency sound waves are produced by a transducer while in contact with the skin.

Pulses of sound waves are reflected back (echoed) to the transducer at interfaces between and within body tissues

A white dot is placed on the monitor screen where the positions from which each echo occurred

The dots create a cross section image of the anatomy at the projected plane of the transducer on the body.

47
Q

Describe an ultrasound within a fluid collection.

A

A fluid filled structure without debris will not have any interfaces within it to reflect sound, so the fluid will be anechoic – the image will not have any echoes within the fluid collection

48
Q

Level of gray or brightness on an image

A

echogenicity

49
Q

How is the echogenicity of soft tissue described?

A

The echogenicity (level of gray or brightness on the image) of soft tissue is described in relation to other tissues.

50
Q

Tissue with the same echogenicity as the predominate tissue in the image is

A

isoechoic

51
Q

Tissue with fewer and weaker echoes is darker than the reference tissue and is

A

hypoechoic

52
Q

Tissue with many strong echoes (bright) is

A

hyperechoic

53
Q

Sound travels unimpeded through fluid so echoes deep to a fluid collection are brighter than adjacent tissue

A

> acoustic enhancement

54
Q

Anything that blocks the transmission of sound waves will cause

A

acoustic shadow

55
Q

Use of ultrasound is limited when…

A

gas-containing or bony structures are in the field of view of a transducer or when the patient is obese

Ex. tail of pancreas may not be seen due to bowel gas shadowing, and chest or upper abdomen may have shadows from the ribs that may obscure parts of the spleen or liver.

56
Q

Medical risk to the patient with ultrasuond

A

No medical risks to a patient from an ultrasound exam with little or no patient discomfort

57
Q

Ultrasound vs MRI & CT

A

Less expensive that CT or MRI, also portable

Tends to be more difficult to interpret than CT, MRI, or radiography – display of structures depends on orientation and angulation of transducer – examiner uses whatever position that maximizes the visualization of the structure being studied.

58
Q

Ultrasound orientation

A

Images are rarely oriented along strict anatomic planes, so interpretation depends on recognizing patterns of structures

59
Q

Ultrasound units can identify, characterize, and quantify moving fluid, usually blood, using

A

Doppler Principles

60
Q

Doppler can look at

A

Can look at tubular structures based on direction and velocity of fluid flow, and abnormal flow can be identified.

61
Q

Doppler is useful for

A

vascular studies

62
Q

Where are ultrasound units becoming more prevalent?

A

ED
Special Clinics
Primary Care

63
Q

Ultrasound images are very…

A

Very operator dependent – identifying free fluid in the abdomen after trauma may be pretty easy, but identifying a rotator cuff tear is much more difficult

64
Q

What can have an effect on ultrasound image quality?

A

body habitus

65
Q

Images close to being in the axial plane should be viewed in the same orientation as

A

axial CT images

66
Q

Images close to the sagittal plane are shown as if

A

the viewer is looking at those sections from the right side of a supine patient with the cranial end of the patient to the viewer’s left and the caudal end to the viewer’s right.

67
Q

Types of Ultrasound

A 
A-Mode
B-Mode
M-Mode
Doppler
Duplex
68
Q

Simplest type of ultrasound

A

A-Mode

69
Q

spikes along a line represent signal amplitude at a certain depth – used mainly in ophthalmology

A

A-Mode Ultrasound

70
Q

mode most often used in diagnostic imaging – each echo depicted as a dot, can show real time motion

A

B-Mode Ultrasound

71
Q

used to show moving structures such as blood flow or motion of heart valves

A

M-Mode Ultrasound

72
Q

assesses blood flow, so used in vascular ultrasound

A

Doppler

73
Q

used in vascular studies – uses both gray-scale and color

A

Duplex Ultrasonography

74
Q

_____________

A

to visualize structure and flow within a vessel and spectral waveform Doppler to quantitate flow

75
Q

Combines studying the morphology of the blood vessels with a recording of the velocity of flow displayed by the Doppler spectral waveform

A

Duplex Sonography

76
Q

a graph of velocity of flow over time within a given area

A

Doppler Spectral Waveform

77
Q

Doppler Spectral Waveform

Flow towards the transducer is displayed

A

above the baseline

78
Q

Doppler Spectral Waveform

Flow away from the transducer is displayed

A

below the baseline

79
Q

Color flow Doppler imaging adds

A

superimposed moving blood shown in color over a gray scale image of the structure – easier to identify abnormalities

80
Q

Study of choice for noninvasive assessment of atherosclerotic disease

A

Carotid Ultrasonography

81
Q

_________ accounts for more than 1/2 of strokes

A

Carotid Disease

82
Q

Used to evaluate bruits, as preop screening prior to other major vascular surgery, and to assess the patency of the vessel after endarterectomy

A

Carotid Ultrasonography

83
Q

Carotid stenosis causes elevations in velocity of flow when >_______ narrowing of the lumen

A

50%

Significant stenosis alters the Doppler waveform proximal, at and distal to the stenosis

84
Q

Venous Duplex

Ultrasound for evaluating for DVT is performed by examining

A 
the leg along the 
common femoral vein
proximal deep femoral vein
greater saphenous vein
popliteal vein
85
Q

What is most sensitive in symptomatic patients who have symptoms above the knee

A

Venous Duplex

86
Q

Veins with thrombi will not

A

Compress

Normal venous structures will easily be compressed and completely collapsed by the transducer

Will also try to visualize the echogenic thrombus itself

87
Q

Ultrasound of the Heart

A

Echocardiography

88
Q

Echocardiography provides information on

A

cardiac great vessel anatomy

89
Q

Echocardiography + Doppler provides information on

A

cardiac and great vessel blood flow.

90
Q

Echocardiography can assess

A 
ventricular function
valvular heart disease 
myocardial disease
pericardial disease
intracardiac masses
aortic abnormalities
91
Q

Echo + Doppler can evaluate

A

cardiac chamber function
valvular function
shunts seen in congenital heart disease

92
Q

Benefits of echocardiography

A

Noninvasive, relatively inexpensive, no radiation, can be performed at bedside in critically ill patients

Results are immediately available

93
Q

How can echocardiography be done if you cannot get a good image?

A

Transesophageal

94
Q

Echocardiography + Stress testing can assess

A

ischemia by wall motion analysis of LV function

Radiology Exam 2 (1 decks)

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