describe zipper artifacts appearance, cause and remedy.
Appearance-zipper artifact appears as a dense line on the image at a specific point.
Cause- outside Rf- a leak of RF
Remedy- check to see if the door is
shut or call engineer to locate leak and repair.
A______ best describes a chelate?
Brain activity consuems oxygen, causing deoxyhemoglobin to _______ the MR signal.
Gadolinium based agents are ________.
in BOLD imaging, normal brain activity will result in the________MR signal.
The time required for molcules to diffuse or move from one medium to another is express by the_________.
Motion is always seen in the _________ on an MRI image.
Protons that come into contract with gadolinum contrast will experience ____________.
A shorter T1 relaxation.
What are the Red Boxes?
On a normal pulse sequence TR or repetition time marks the beginning and end of the data acquisition. The cardiac MRI imaging there is no TR. so the _________ marks the beginning and end of the data axquisition.
The principal time restraints in cardac imaging is the filling of k-spaces. What are the 3 ways to reduce time by the way k-space is filled?
1.Half fourier- mirroring data to fill k-space quicker.- only half of k-space is filled and mirrored to the other side. A few lines in the center of k-space may be acquired to increase snr.
2.Segmentation- essentially is when multiple phase encoding signals are acquired during a single heartbeat. Complete k-space is filled over 10-20 heartbeats. Segmentation of k-space can be implemented to produce multiple image planes.
3.Spiral filling- k-space is filled from the center out in a spiral fashion so that more data is located in the center, this provides improved contrast resolution and faster imaging times.
What are the 2 aspects that must be evaluated for all breast tumors using contrast MRI are?
1) must determine if the breast tumor demonstartes contrast enhancement, rapid and intesne enhancement are reported characteristic features of malignant breast tumors
2) Must evaluate the appearance of the tumor-irregular shape and spiculated borders. Tumors may also show ring enhancement
The most common pulse sequence for perfusion scanning is?
Why is mammo the gold standard for breast screening?
Most masses can be seen on mammography. Mammography is less sensitive to dense breast as seen in this image. MRI is used in conjunction with mammography and ultrasound. Mri is not approved as a screening tool unless you are at high risk.
In diffusion imaging, random motion of molecules from a region of high concentration to an area of low concentration is know as__________. This is relavant in that it plays a vital role in detectiv CVAs earlier that any other modaliyt where aggressive treatment may be utilized to reverse tissue damage.
Be able to descibe BOLD imaging and nake sure you can include deoxyghemoglob and oxyhemoglobin the the discription.
Blood oxygen level dependent, requires two images. Normal vasculature with mix of oxyhemoglobin and deoxyhelmoglobin. Brain activity consumes oxygen causing deoxyhemo. to form reducing signal. Replacement oxyhemoglobin results in increased signal.
What are the disadvantages of exogenous contrast administration?
Expensive, invasive, added time
The most common pulse sequence used for diffusion imaging in MRI is the_______?
spin echo pulse sequence
________ in MRI alter the MR signal indirectly by shortening the relaxation time.
aliasing or wrap
The three gradient magnetic fields are used for spatial localization in the diffusion imaging. In addition to this, one of the gradients is energized breifly just prior and just after the 180 degree pulse. This is called________.
post contrast images are always_____
t1 weighted images
cardiac funtion is best visualized by?
The______artifact appears as a band at low and high signal interfaces.
T/F: diffusion occurs at a lower anatomical level than perfusion?
The most common rendering utilized MRA is ______ which is displayed in the below image..
_____ is magnetic resonance angiography imaging technique that relise primarily on the flow related enhancement to distinguish moving from stationary protons.
What are the indications for an MR Breast exam.
Dense breast, family history of breast cancer, evaluation of breast impants, and staging of breast cancer
What is the difference between time of flight and Phase contrast MRA?
time of flight- most common- relies on the flow related enhancement to distinguish moving from stationary
phase contrast- occurs during signal sampling under the influece of frequency encoding read gradient magnetic field spins moving in the direction of Br experience a shift, resulting in a phase contrast effect
Contrast agents originates outside of the organ or tissue is?
The pulse sequences that are used to scan the breast in MRI are:
T1 sagittal fat supression, axial inversion recovery, 2D application/3D application GRE, and Post contrast T1 sagittal
The _____ plane can be obtained by using the HLA or horizontal long axis view to prescribe an oblique plane through the right and the left ventricles by placing the slices perpendiucalr to the interventricular septum.
Know which image is used to plan which cardiac imaging planes.
vertical long axis
Be able to identify which of the 3 planes used in cardiac imaging is displayed which observing the image.
Vertical Long= left atrium and left ventricle
Horizontal Long= 4 cardiac chambers
List the 4 most common pulse sequences used in Cardiac MRI.
Cardiac anatomy= spin echo
Cardiac function= cine gre
Mycardial profusion= BOld Gre-Epi
Coronaries or Aorta= MRA
If the cardiac frequecy is 60 beats/min what is the time of the required cycle and therefore the requried TR?
60 beats/60 s
1 beat/1000 ms
TR= 1000 ms
Name the 3 off axis cardaic imaging planes and describe the planning of successive acquisions of the hearts long and short axis.
vertical long axis
oblique plane it can be obtained by using the HLA to prescribe an oblique plane through the right and left ventricle by placing the slicees perpindicular to the interventricular septum.
vertical long axis
plug=uniform blood flow, flow profile in which the center of the vessel is the same as that along the wall
Laminar=blood flowing the in layers; max blood flow in the center of a vessel and slow near the vessel wall
blood flow with a random velocity in profile- results in spin dephasing and signal loss
pulsatile= blood flow in the arteries.
stoping motion by acquiring data only during a specified portion of the cardiac cycle, typically during diastole when the heart is not moving. Images are created from data collected over a series of cardiac cycles. R to R.
ecG gating uses the hearts electrical activity to trigger data axquisison in cardiac mri using gating technuques the rr interval triggers the mr sequences
What is MRA utilized over conventional angiographic methods?
no iodizing radaiton, non iodinated contrast is used(great for allergies), no hospital stay, outpatient setting
Flow Related Enhancement=
Flow Compensation= use of bipolar gradeint magnetic fields to reduce flow artifacts by reestablishing phase coherence; first order gradent moment nulling
Flow Related Enhancement= the increase in signal intensity of flowing blood compared with stationary tissue when fully magnetized spins replace saturated spins between RF pulses
Flow Void= Flow void pure and simple occurs when fast moving blood leaves the imaging slice before receiving the 180 rephasing pulse.
_______ uses the velocity differences and hence the phase shifts in moving spins to provide image contrast in flowing vessels.
What is the difference between 2D and 3D MRA?
2D- slow (used for imaging vein) slice thickness 1-3 mm uses suquential acquistions