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Radiology Exam 2 > Lecture 13 - MRI > Flashcards

Lecture 13 - MRI Flashcards

(94 cards)

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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
Who should not receive Gadolinium?
Pts with renal insufficiency
26
What can patients with renal insufficiency develop after Gadolinium?
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
27
What has better soft tissue resolution?
MRI MRI>CT for soft tissue resolution.
28
If contrast is indicated and CT and MRI are equivalent but contrast is contraindicated, what do you use?
unenhanced MRI is usually better than unenhanced CT
29
What must be removed from the patient before an MRI?
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
30
What foreign bodies can cause an issue with MRIs?
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
31
MRI Safety during pregnancy
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.
32
MRI safety with metal objects
Some may still have an MRI depending on the metals used, the shape of the objects, and the location involved.
33
Issues with MRI
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
34
What images can MRI provide?
Axial Sagittal Coronal Just like CT
35
MRI is used for...
``` Musculoskeletal Neurologic GI Endocrine/Reproductive GU ```
36
What does a Musculoskeletal MRI evaluate?
``` Bone marrow Menisci Tendons Muscles Bones Osteomyelitis Spine ```
37
What is a Musculoskeletal MRI used for?
``` 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 ```
38
A musculoskeletal MRI has a __________ negative predictive value if normal.
High
39
Neurologic MRI evaluates...
``` Brain - especially the posterior fossa Tumors Infarction Multiple Sclerosis Peripheral nerves looking for impingement or injury. ```
40
GI MRI evaluates...
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
MRI Liver evaluation includes
``` Characterizes liver lesions Detects small lesions Cysts Hemangiomas Hepatocellular carcinoma Hemochromatosis Fatty infiltration ```
42
MRI Biliary system evaluation includes.
MR cholangiopancreatography for strictures | Ductal dilatation
43
MRI evaluation of the small and large bowel:
MR enterography | Appendicitis in pregnancy
44
MRI Endocrine/Reproductive evaluation includes:
Evaluates the adrenal glands – adenomas, adrenal hemorrhage Evaluates the male pelvis – staging of rectal, bladder, and prostate carcinoma
45
MRI of the GU evaluates
Renal Masses | Cysts vs Masses
46
How does Ultrasound work?
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
Describe an ultrasound within a fluid collection.
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
Level of gray or brightness on an image
echogenicity
49
How is the echogenicity of soft tissue described?
The echogenicity (level of gray or brightness on the image) of soft tissue is described in relation to other tissues.
50
Tissue with the same echogenicity as the predominate tissue in the image is
isoechoic
51
Tissue with fewer and weaker echoes is darker than the reference tissue and is
hypoechoic
52
Tissue with many strong echoes (bright) is
hyperechoic
53
Sound travels unimpeded through fluid so echoes deep to a fluid collection are brighter than adjacent tissue
>acoustic enhancement
54
Anything that blocks the transmission of sound waves will cause
acoustic shadow
55
Use of ultrasound is limited when...
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
Medical risk to the patient with ultrasuond
No medical risks to a patient from an ultrasound exam with little or no patient discomfort
57
Ultrasound vs MRI & CT
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
Ultrasound orientation
Images are rarely oriented along strict anatomic planes, so interpretation depends on recognizing patterns of structures
59
Ultrasound units can identify, characterize, and quantify moving fluid, usually blood, using
Doppler Principles
60
Doppler can look at
Can look at tubular structures based on direction and velocity of fluid flow, and abnormal flow can be identified.
61
Doppler is useful for
vascular studies
62
Where are ultrasound units becoming more prevalent?
ED Special Clinics Primary Care
63
Ultrasound images are very...
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
What can have an effect on ultrasound image quality?
body habitus
65
Images close to being in the axial plane should be viewed in the same orientation as
axial CT images
66
Images close to the sagittal plane are shown as if
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
Types of Ultrasound
``` A-Mode B-Mode M-Mode Doppler Duplex ```
68
Simplest type of ultrasound
A-Mode
69
spikes along a line represent signal amplitude at a certain depth – used mainly in ophthalmology
A-Mode Ultrasound
70
mode most often used in diagnostic imaging – each echo depicted as a dot, can show real time motion
B-Mode Ultrasound
71
used to show moving structures such as blood flow or motion of heart valves
M-Mode Ultrasound
72
assesses blood flow, so used in vascular ultrasound
Doppler
73
used in vascular studies – uses both gray-scale and color
Duplex Ultrasonography
74
_____________
to visualize structure and flow within a vessel and spectral waveform Doppler to quantitate flow
75
Combines studying the morphology of the blood vessels with a recording of the velocity of flow displayed by the Doppler spectral waveform
Duplex Sonography
76
a graph of velocity of flow over time within a given area
Doppler Spectral Waveform
77
Doppler Spectral Waveform Flow towards the transducer is displayed
above the baseline
78
Doppler Spectral Waveform Flow away from the transducer is displayed
below the baseline
79
Color flow Doppler imaging adds
superimposed moving blood shown in color over a gray scale image of the structure – easier to identify abnormalities
80
Study of choice for noninvasive assessment of atherosclerotic disease
Carotid Ultrasonography
81
_________ accounts for more than 1/2 of strokes
Carotid Disease
82
Used to evaluate bruits, as preop screening prior to other major vascular surgery, and to assess the patency of the vessel after endarterectomy
Carotid Ultrasonography
83
Carotid stenosis causes elevations in velocity of flow when >_______ narrowing of the lumen
50% Significant stenosis alters the Doppler waveform proximal, at and distal to the stenosis
84
Venous Duplex Ultrasound for evaluating for DVT is performed by examining
``` the leg along the common femoral vein proximal deep femoral vein greater saphenous vein popliteal vein ```
85
What is most sensitive in symptomatic patients who have symptoms above the knee
Venous Duplex
86
Veins with thrombi will not
Compress Normal venous structures will easily be compressed and completely collapsed by the transducer Will also try to visualize the echogenic thrombus itself
87
Ultrasound of the Heart
Echocardiography
88
Echocardiography provides information on
cardiac great vessel anatomy
89
Echocardiography + Doppler provides information on
cardiac and great vessel blood flow.
90
Echocardiography can assess
``` ventricular function valvular heart disease myocardial disease pericardial disease intracardiac masses aortic abnormalities ```
91
Echo + Doppler can evaluate
cardiac chamber function valvular function shunts seen in congenital heart disease
92
Benefits of echocardiography
Noninvasive, relatively inexpensive, no radiation, can be performed at bedside in critically ill patients Results are immediately available
93
How can echocardiography be done if you cannot get a good image?
Transesophageal
94
Echocardiography + Stress testing can assess
ischemia by wall motion analysis of LV function

Radiology Exam 2 (1 decks)

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