COMPLETE LIST OF QUESTIONS

Magnets and Scanners

     Basic Electromagnetism»

• What causes magnetism?
  
• We have a 3.0 Tesla MR scanner at our hospital.  I know this is a very strong magnet, but what exactly is a tesla? 
  
• Who was Tesla?  What did he do so great to deserve having the magnetic field named after him? 
• I've heard magnetic fields are also measured in gauss.  What's the difference?
  
• I still don't have a good idea of how strong 3.0T is.  How does it compare to a refrigerator magnet or the big magnet in a junkyard that picks up cars?
• What is a gradient? 
  
• I'm confused.  Isn't a gradient some type of coil?
• What is magnetic susceptibility?  
  
• What causes susceptibility?  
  
• I saw on the internet a video of a frog floating in a magnet.  How does that happen?  Did the frog become magnetized?  
  
• What is ferromagnetism? 
  
• What's so "super" about superparamagnetism?

     Magnets - Part I»

• There seem to be many different MRI magnets and designs.  Can you explain?
  
• How many brands of scanners are there? 
  
• Which way does the main magnetic field point in an MR scanner? 
  
• Which end of a scanner is the north or south pole? 
  
• How do you define low-, mid- and high-field? 
  
• Most magnets sold today are of the high-field superconducting.  Why would anyone want to buy a lower field strength scanner?  
  
• Aren't there some major disadvantages to lower field strength scanners? 
• An MR salesman claims his scanner has better "homogeneity" than that of his competitor. What is he talking about? 
• How important is good homogeneity?  
  
• What is shimming and why is it needed?
  
• How is passive shimming performed? 
  
• How does active shimming work?  
  

     Magnets - Part II»

• What causes superconductivity?
  
• Isn't superconduction like perpetual motion? Doesn't the current in the superconducting coils ever slow down? 
  
• If the magnet coils are in a closed superconducting loop, how do you get current into them to ramp up the field initially?  
  
• How are superconducting scanners constructed?  
  
• I've heard about room temperature superconductors.  Will MR magnets of the future be made of these materials?
  
• Don't superconducting scanners consume liquid helium?  How often does it need to be replenished? 
  
• What is a quench? 
• Is the magnetic field turned on and off between patients? 
  
• Does the scanner have an emergency "stop" button? 
  

     Gradients»

• What are gradient coils?
  
• How do you make a z-direction gradient?
  
• How do you make x- and y-direction gradients? 
  
• All the diagrams I have seen for gradients deal with cylindrical scanners. How are the gradients designed for open-bore scanners? 
  
• I've heard that "eddy currents" cause problems for imaging.  What are they? 
• What are actively shielded gradients?
• I'm confused.  I thought active shielding had to do with controlling the main magnetic field.  
  
• What is pre-emphasis and how does it reduce eddy currents?  
  
• Why do the scanner walls get so warm?  
  
• The MR sales representative is telling me about his scanner's strong gradients. How do I interpret the specification sheet?
  
• What about specifications for linearity?  
  

     RF & Coils»

• I don't understand all the different types of coils in MR.  Can you make sense of these?
• What are radiofrequency (RF) waves and how are they produced?
  
• I know I was taught this in school, but can you briefly review the difference between phase and frequency?
  
• What are the function(s) of radiofrequency (RF) coils? 
• How do RF-transmit coils work?  
  
• What is the difference between linearly polarized (LP) and a circularly polarized (CP) coils? 
  
• Several manufacturers recently started offering "multi-transmit" technology. What is it and how does it work? 
  
• How do receive-only coils work?  
  
• What is the difference between phased and parallel coil arrays?
  

     Site Planning»

• What are the components of a complete MR system and where are they located?
• What are fringe fields and why do they matter?  
  
• What are the ACR Safety Zones?
  
• How do you reduce the size of the fringe field so it doesn't cause problems?
  
• Does magnetic shielding also keep out stray magnetic fields and electrical interference? 
  
• Prior to adding on a new MRI bay we were told we need to have vibration testing performed.  Why is this necessary?  
  
• What's all that noise the scanner is making?
• What is the purpose of RF-shielding?  
  
• If the scanner room is shielded against radiofrequencies, how do you get tubes, pipes and wires through the walls?  
  

Safety and Screening

     Overview»

• What are the ACR Safety Zones?
• How do you screen patients for implants and foreign bodies prior to MRI?
• What do you do about screening if the patient is unconscious or can't answer all questions on the form?
• What are the risks of passive vs active implants in MRI?
• What does it mean when an implant or device is labeled "conditional"?
• What are the most common safety screening scenarios and how do you handle them?
• Have you ever had a significant ferromagnetic projectile event or injury at your MR site? 
• Should MRI facilities screen patients with metal detectors? 
• Does MRI pose any risk to the developing fetus?  Do you scan pregnant patients?  
• What are the specific safety hazards in dealing with sick patients from the operating room, ICU, or ER?  ​​

     Static Fields»

• Which types of metal are the most dangerous around a magnetic field?  
• The effect of object shape seems obvious. A long, pointy object is more dangerous than a smooth, round one, right?   
• How do you calculate the magnetic force pulling a piece of metal toward the scanner?  
• So then, exactly where is the most dangerous place for force or torque near an MRI scanner? 
• How are translational force and torque measured for an implant?   
• Do the strong static magnetic fields used in MRI pose any health risks?    
• What causes some patients to experience dizziness and/or vertigo in an MR scanner?  
• What causes the flickering lights observed by some MRI patients?  
• Some patients undergoing MRI report a metallic taste. Is that due to an effect on dental fillings?   
• What adverse health effects are associated with MR scanner acoustic noise?
• I've heard MRI may cause a patient's arm or leg to twitch during scanning. What causes this? Is it dangerous?​​

     RF Fields»

• How do radiofrequency fields affect biological tissues? 
• What is SAR?
• What are the absolute SAR limits you are not permitted to exceed?
• What is meant by the term "operating mode" of an MR scanner?
• What practical steps can a technologist use to reduce SAR?   
• How do burns occur in MRI? 
• What causes implants to heat up during MR imaging?
• How does one measure or estimate MRI-related implant heating?
• What is SED? Is it better measure of heating than SAR?
• What is B1+ rms? Is it a better metric for energy deposition than SAR?
• Does working around the electromagnetic fields of an MRI scanner carry any health risks? Should exposure be limited? What about pregnant techs and staff? 
  
• Is it safe to live under power lines, use a cell phone, or sleep under an electric blanket at night? ​

     MR Safety: Neurological»

• Which aneurysm clips are MR Unsafe? What about endovascular aneurysm coils?
• What safety precautions must be taken if a patient has a cerebrospinal fluid shunt? 
• Can patients with intracranial pressure monitors be scanned? 
• Can patients with deep brain stimulators be scanned?
• Can patients with spinal cord stimulators undergo MRI? 
• Can vagal nerve stimulators be safely scanned? 
• What MRI limitations are there for scanning epilepsy patients with superficial or depth electrodes?
• What do we do if we encounter a carotid artery clamp?
• How do you deal with peripheral nervous system stimulators from an MR safety perspective?  
• Can patients with epidural or perineural catheters be safely scanned?   

     MR Safety: Head and Neck»

• Besides foreign bodies, are there any other eye-related potential hazards to be aware of in MRI?
• Can you scan someone with a cochlear implant?
• Are bone conduction implants safer than cochlear implants for MRI?
• What other types of otologic devices should be viewed with concern for MRI?
• Must a patient remove dentures and other oral prosthetics before MRI?  
• Can patients with ET tubes and other upper airway devices undergo MR?

     MR Safety: Chest and Vascular»

• What's the danger with breast tissue expanders in MRI? 
• Which breast biopsy devices and markers are MRI compatible?
• What do you do about tracheobronchial airway devices like stents, valves and coils? 
• ​Are respiratory stimulation systems for diaphragmatic paralysis and sleep apnea safe for MRI?
• Any special precautions in patients with vascular access ports? 
• I heard Swan-Ganz catheters can melt in the MRI. Are any similar devices safe to scan? 
• Is there an increased risk of IVC filters moving during MRI? 
• What are the specific MR precautions with implanted infusion pumps? 
• How about insulin pumps and continuous glucose monitors (CGMs)? 
• Are all stents and stent grafts safe to scan? Isn't there a waiting period after implantation? 
• Any problems scanning patients with sternal wires after cardiac surgery?

     MR Safety: Cardiac»

• Do pacemakers stop working in an MRI scanner? Why are older pacemakers dangerous to scan? 
• ​I'm not a cardiologist. Can you explain some of the pacemaker types and terminology relevant to us working in MRI?
• Aren't new pacemakers safe to scan in MRI? Any limitations?
• What precautions must be taken to scan patients with older/legacy/non-conditional pacemakers?
• How strictly must one follow the MR conditions for CIEDs if you feel a patient needs an MRI scan? Which can be violated with the least risk?
• What about epicardial CIED's and their abandoned leads?
• ​Can we scan patients with loop recorders and other internal cardiac monitors? 
• Can patients with metal heart valves be safely scanned?  
• Are there other cardiovascular devices with MR safety issues we should know about?  ​

     MR Safety: Abdominal (GI/GU)»

• Can I scan a patient with a retained PillCam™?
• I assume that gastric pacemakers are forbidden in MRI. Correct?
• What other GI devices warrant concern for MRI screening?
• What about contraceptive devices like diaphragms and IUDs? Could their movement result in pregnancy? 
• Are Foley catheters safe for MRI?
• What about the safety of incontinence devices such as pessaries and artificial sphincters?
• What about penile implants?
• What precautions must be taken when scanning patients with an InterStim® or other sacral neurostimulator? 
• How about other GU devices like nephrostomy tubes and stents?​

     MR Safety: Orthopedic»

• Can one safely scan patients with total joints and other orthopedic hardware like plates and screws? 
• ​How can you tell if an external fixation device is safe for MRI?
• ​What are the MR safety issues for patients with skeletal or cervical traction? 
• ​Can patients with implanted bone growth stimulators be safely scanned?
• What are magnetic growing rods and are they MR compatible? 

The NMR Phenomenon

     Spin»

• What is spin? 
  
• Why are the allowable values for spin either whole or half integers? Why couldn't all the spins be whole numbers, or for that matter, any value whatsoever?
• You seem to use terms nuclei, protons, and spins interchangeably, but aren't these different things?  
  
• How do you predict the value of nuclear spin (I) based on the number of protons and neutrons?  
  
• What is the gyromagnetic ratio (γ)?  
  
• What is the difference between "spin" and "spin state"?
  
• Why do spin-up and spin-down states have different energies?
  
• If a system seeks to minimize its total energy level, why don't all the protons simply reside in the lower energy spin state?
• Nearly all the books and papers I have seen show diagrams of protons flipping from spin-up to spin-down states. Are you telling me these are all wrong?    
  

     Precession»

• All the NMR books all show protons precessing like little tops or gyroscopes within the magnetic field. I don't really understand why this type of motion should occur. Can you explain? 
• Who was Larmor and how did he discover his famous frequency?  
  
• Where does the energy come from to keep the precession going?
• What is meant by a chemical shift?   
  
• What is net magnetization and how does it apply to NMR?
  
• Does the net magnetization (M) just instantly appear?  
  
• I know that individual nuclei precess, but does the net magnetization (M) also?
• Is nuclear precession the same as resonance?   
  

     Resonance»

• You seem to use MR, MRI and NMR interchangeably.  Are there any differences among these terms?  
  
• Who discovered NMR? 
  
• How does B1 tip the net magnetization (M)?
• Why does the RF-field have to be applied at the Larmor frequency for resonance to occur?
  
• What is meant by flip angle?  
  
• Are the individual nuclei still precessing after a 180°-pulse? 
• Why are all the spins brought into phase with one another after a 90°-pulse?  I don't understand why this should happen.  
• When a group of spins is driven into higher energy levels by the action of an RF field, why don't these spins immediately release the absorbed energy and drop back to their original lower energy states? 
•  What is the rotating frame of reference? 
• What happens if the B1 field is applied "off resonance" (i.e., not exactly at the Larmor frequency)?  
  
• What is adiabatic excitation?  
  
• How do adiabatic pulses differ from regular Rf-pulses? What are they used for?  
  

     Relaxation: Physics»

• What are the Bloch equations?
• What is T1 relaxation?
• What is T2 relaxation?    
• What is the difference between relaxation rates and relaxation times?
• Why is T1 longer than T2?  
• What is the difference between T2 and T2*?  
• What are the causes of T1 and T2 relaxation?
• Can you explain a little more about the dipole-dipole interaction? I still don't quite understand. 
• What do you mean by chemical exchange and how does it effect T1 and T2?
• What are spin-spin interactions?  
• How does the presence of macromolecules affect T1 and T2?  
• I'm getting confused. You've been talking about all kinds of nuclei -- in fat, water, and macromolecules. Which hydrogen protons are producing the MR signal? 
• What is magnetization transfer?
• How do T1 and T2 values vary as a function of field strength?
• How can you predict the T1 and T2 values of different tissues?    
  

     Relaxation: Clinical»

• Why is fat bright on T1-weighted images? 
• Are there other fats and oils that produce a bright T1 signal?  
  
• What about cholesterol? You haven't mentioned its T1 brightening, but that's in "all the books".  
  
• Why are calcifications sometimes bright on T1-weighted images?
• Why is meconium bright on T1-weighted images?   
  
• Why is melanin bright on T1-weighted images?  
  
• Why is proteinaceous fluid bright on T1-weighted images?
  
• How is contrast generated by magnetization transfer? Also, what are MTI, MTC, and MTR?  
  

Pulse Sequences (Basic)

     MR Signals»

• Where does the MR signal come from?  
• What is a free induction decay (FID)?  
• What is a gradient echo, and how does it differ from an FID?  
• What are TR and TE?
• How is a spin echo generated? 
• You mentioned that other pulses besides a 90°-180° combination can produce a spin echo.  I don't see how this happens.  Can you explain? 
• What is a stimulated echo?
• Are stimulated echoes used for imaging?  I've never heard of that. 
• If a spin echo results from 2 pulses, and a stimulated echo from 3 pulses, what do you get from 4 pulses? 
• What is a partial flip angle pulse, and why would you want to use one?  
• Wait a minute! If a partial flip angle pulse tips less magnetization into the transverse plane than a 90° pulse does, how can the signal be higher?  
• How do you pick the "optimum" flip angle?  
  

     Spin Echo»

• What is the difference between spin echo, multi-spin echo, and fast spin echo? 
  
• I know long TR/TE gives T2-weighting and short TR/TE gives T1-weighting, but I don't understand why.  Can you explain? 
  
• Long T1 materials are dark on T1-weighted images, but long T2 materials are bright on T2-weighted images. And vice versa.  Why don't these behave the same way?
  
• What is meant by a T1- or T2-weighted image?
• If the SE is able to recover components of the FID lost by field inhomogeneities, why doesn't it correct for T2 decay as well?  
• Why doesn't the 180° refocusing pulse also invert the longitudinal magnetization in addition to flipping over the spins in the transverse plane?
• Diagrams always seem to show the 180° pulse flipping the spins over the top right side of the transverse plane.  Why don't the spins flip 180° in some other direction, for example, below the transverse plane and to the left?    

     Inversion Recovery»

• What is the inversion recovery pulse sequence?
  
• Why use IR? What are the advantages? 
  
• What is phase-sensitive IR and why does it have a gray background?
  
• If phase-sensitive IR provides more information than magnitude reconstructed IR, why not use it all the time? 
  
• How do you set the IR parameters to achieve desired image contrast?  
• How do you pick a TI value to null signal from a given tissue?
• What is STIR?  
• What is T1-FLAIR? 
• What is T2-FLAIR?  
• What is meant by an "IR-prepped" sequence? How is this different from "standard" inversion recovery?  
• What is meant by "double" IR?  
  

     Gradient Echo»

• How does a gradient echo differ from a spin echo?
• How do you produce multiple GRE's from a single pulse?  
• There are so many different GRE sequences. Can you make sense of these?  
• It seems as if every manufacturer has adopted a different name for their gradient echo sequences. Why is this? Can you sort this out for me?
• What is meant by spoiling, and how is it accomplished?  
  
• Why would you want to use a spoiled-GRE technique?  How do you pick the parameters?
• I'm confused. Isn't a spoiled-GRE sequence T1-weighted by definition?
• What is meant by steady-state free precession (SSFP)? 
• How do GRASS/FISP sequences work?
• How do you select imaging parameters for GRASS/FISP sequences? 
  
• What is the difference between single-slice GRASS and multi-planar GRASS (MPGR)?  
• What is the difference between FISP and PSIF? 
• What is True FISP, and why is it "truer" than regular FISP? 
• What is the difference between FIESTA and FIESTA-C? 
• What is DESS? 
• We have been using a sequence called MERGE for spinal imaging that shows excellent contrast between cord, CSF and disk. How does this work?  
• What is GRASE?  
  
• What is the difference between MP-RAGE and MP2RAGE?  

     Susceptibility Imaging»

• What is susceptibility?  
• Must I buy expensive new SWI software? What's wrong with using T2*-GRE sequences instead? 
• How are susceptibility weighted images obtained and processed?  
• How do you distinguish blood from calcifications on SWI phase maps?
• Can susceptibility differences be accurately quantified?  

     Diffusion: Basic»

• What is diffusion?
• What is the difference between isotropic and anisotropic diffusion?
• What is the difference between the diffusion coefficient (D) and the "apparent" diffusion coefficient (ADC)?
• How do you make a DW image?
• What is meant by the b-value?  How do I pick it?   
• In body imaging a starting b-value of 50 (s/mm²) instead of b=0 is often used. Why is this?
• What is the Trace DW image? How does it differ from the ADC map?
• If a stroke is bright on a standard DW image, why is it dark on the ADC map?
• What is T2 shine-through?
• How does the "exponential" ADC map differ from a "conventional" ADC map?  
• I know what T2-shine-through is, but what is T2-blackout?
• Which diseases are "bright" on DW imaging and why?  

     Diffusion: Advanced»

• What is the diffusion tensor? How is this different from "regular" diffusion?
• What is Diffusion Tensor Imaging (DTI), and how does it differ from "regular" diffusion-weighed imaging? 
• How is whole-body DWI performed and why should I use it?
• Why does readout-segmented DWI produce better looking images? 
• I've seen high-resolution, small field-of-view DW images of the prostate. How do these sequences work? 
• What is intravoxel incoherent motion (IVIM)? Is this the same as diffusion? 
• What is diffusion kurtosis and how does it differ from regular "diffusion"?  

     Fat-Water Imaging»

• What makes fat and water behave so differently on MRI?
• What is meant by the fat/water chemical shift? How is it calculated?
• What is meant by in-phase vs out-of-phase imaging?
• There seem to be many methods available for fat suppression. Which one is the best?
• What is the Dixon method of fat suppression? When should it be used?
• How do Fat-Sat pulses work?
• Our scanner offers an option called "Water Excitation". Is this just another name for Fat-Sat?
• What is STIR?
• What is SPIR and how does it compare to other fat suppression methods?
• What is SPAIR? How is it different than SPIR?
• What are the differences between SPAIR, SPIR, and STIR? When should each be used?

Making an Image

      From Signals to Images»

• I know I was taught this in school, but can you briefly review the difference between phase and frequency?  
• What is the difference between "regular" frequency (f) and angular frequency (ω)?  
• The MRI signal just looks like a "squiggle". How does it contain all the information needed for imaging?
• What is the difference between real and imaginary signals? How can one be more real than another?  
• What is a Fourier transform?  
• What are 2D- and 3D-Fourier transforms? I don't see how FT works in higher dimensions.
• Who invented MR imaging?  
• How does the scanner know the locations of all the MR signals? 

      Frequency Encoding»

• How does frequency-encoding work?  
• What is bandwidth? 
• What is narrow bandwidth, and when would you want to use it?  
• How does frequency-encoding let you stimulate a given slice?  
• Drawings of the slice-select gradient often have a little downward lobe at the end. What is this for? 
• What is cross-talk and what can be done about it?  
• Why not just frequency-encode all the voxels?
• How does the MR scanner keep track of which signal comes from which slice?  
• Can you excite more than one slice simultaneously?  

      Phase Encoding»

• Why do some gradients change frequency and others change phase? It seems like they should do all work the same way.
• If each pixel is assigned a unique phase and frequency, why can't you use just a single phase-encoding step to decode spatial information?
• I understand frequency-encoding, but I just don't get phase-encoding. Can you explain?
• I understand the 2-pixel example, but I still can't put it all together with the whole image and frequency encoding. Can you help?
• I think I see how to calculate pixel values in your simple examples, but how do you do this in a real image with thousands of pixels?
• How do you pick which anatomic direction to use for frequency- or phase-encoding?

      Performing an MR Scan»

• What are the steps a technologist goes through to perform an MRI scan?
• What is the scanner doing during the automatic pre-scan period?
• Is additional shimming really needed as a part of the pre-scan process?
• Why must coil tuning and matching be performed, and how is it done?
• Please explain how and why the center frequency must be adjusted.
• What is the purpose of adjusting the transmitter gain/attenuation?
• Why is receiver gain adjustment necessary? What happens if it is set incorrectly?
• What are dummy cycles and why are they needed?
• Where did my fMRI (or DTI or MRS or perfusion) raw data go?
• What training or certification do you need to become an MRI technologist?

K-Space and Rapid Imaging

      K-space (Basic)»

• What is k-space?
  
• If the points in k-space don't correspond to points in the image, what do they mean?  
  
• What does the letter "k" stand for?
  
• What do you mean by spatial frequency? 
  
• Exactly where are the spatial frequencies are located in k-space?  
  
• Where do you get the data to fill k-space?
  
• I don't understand how you can simply plug the digitized MR signal data directly into k-space. How are these points the same as spatial frequency? 
  
• What is spin-warp imaging? Isn't this just "regular" MRI?  
  
• Why does k-space have a big spot in the middle?  
  
• You alluded to different trajectories for filling k-space. What are they?  
  
• Why would you want to use a radial k-space sampling method?
  


 

      K-space (Advanced)»

• Why is k-space drawn as a grid? What do the axes in k-space mean?
  
• What is the meaning of negative frequencies? I don't understand how kx and ky can have negative values.  
  
• How does k-space relate to field-of-view (FOV) and pixel width?
  
• How does one obtain a rectangular field of view? Why would you want to use it? 
• What is partial Fourier imaging? 
  
• How does phase-conjugate symmetry work? Why is it used?
• What is read-conjugate symmetry (fractional echo) imaging? Why would one only want to sample part of an echo? 
  
• Why don't you combine the read conjugate symmetry and phase conjugate symmetry techniques? That way you really save time by collecting only 1/4 the k-space data. 
  
• A option called ZIP is available for some sequences. Is this a type of file compression? 

      Rapid Imaging (FSE & EPI)»

• What is Fast (Turbo) Spin Echo imaging?
  
• How do you select parameters for fast spin echo imaging? There are several new ones to set. 
  
• Why is fat bright on fast spin echo images?  
  
• Besides bright fat, are there other differences in image properties between conventional spin echo and fast spin echo imaging?  
  
• How does a dual-echo FSE sequence work? It seems there is not enough room for the two sets of echoes.
  
• What is a driven equilibrium (fast recovery) pulse?
  
• Why would you want to use reduced flip angles in FSE? Wouldn't smaller flip angles kill the MR signal?  
  
• What are "hyper-echoes" and how do they differ from regular echoes?
• What are the SPACE/CUBE/VISTA techniques?
  
• What is echo-planar imaging (EPI)? Is this the same as Fast Spin Echo (FSE)?
  
• What is HASTE?
  

      Parallel Imaging»

• What is parallel imaging? How does this differ from "regular" imaging? 
• Isn't parallel imaging (PI) just "regular" MRI using multiple receiver coils? 
• Is PI a special type of pulse sequence? Can it be performed with any coil in any direction?
  
• Should parallel imaging acceleration be used in every case? 
  
• Our scanner has two different options for parallel imaging (SENSE and GRAPPA). What are they and which should I use?  
  
• How does SENSE/ASSET work?
  
• How does GRAPPA/ARC work? 
• What is CAIPIRINHA? Isn't it some sort of a drink?   
• Why do parallel imaging studies look so noisy?
  
•  Are there any artifacts specific to parallel imaging?  
  

Contrast Agents and Blood

      MR Contrast Agents: Physics»

• Why are most MR contrast agents based on the element gadolinium?
  
• How does gadolinium cause relaxation? 
  
• What is meant by the relaxivity of a contrast agent? How is it measured?
  
• Why does gadolinium apparently only shorten T1? Doesn't it have an effect on T2 as well?
  
• Can the T2-shortening effects of gadolinium ever be observed on routine MR imaging?
  
• Does contrast enhancement depend on field strength? Do I need more contrast or less at higher fields?
  
• Is there a best T1-weighted pulse sequence for showing contrast enhancement?
  
• Don't higher doses of contrast show more enhancing lesions? Are there other ways to achieve this effect?
  
• What is dynamic contrast-enhanced (DCE) imaging?
  
• Is iodine contrast visible on MRI? Is gadolinium contrast visible on CT?

      MR Contrast Agents: Clinical»

• So many gadolinium contrast agents are now available. What are the differences among them?   
• What are the important physical properties to consider when choosing a contrast agent?
  
• Are non-ionic gadolinium contrast agents better than ionic ones?
  
• Gd contrast agents are only approved for IV administration, but don't people inject them into joints and the CSF? Is this safe? Is this legal?
  
• Tell me about the liver agent Eovist®. How does it work and when do you use it?
  
• Whatever happened to Teslascan®?
  
• Whatever happened to Feridex®? Aren't iron-containing contrast agents useful for liver MRI?
  
• I have heard there are MR contrast agents for lymph nodes. How do these work?
  
• Do you use bowel contrast agents for abdominal MR imaging?
  
• Whatever happened to Ablavar?

      MR Contrast: Safety»

• How safe are gadolinium contrast agents?
• I've heard the term "anaphylactoid" applied to contrast agent reactions. What is the difference between this and "anaphylactic"?
• Is gadolinium contrast nephrotoxic? Can it be given safely to patients with mild renal insufficiency?
• What is NSF? How does gadolinium cause it?
• Do all MR contrast agents carry the same risk of NSF?
• What kind of informed consent to you give your patients receiving gadolinium? Do you tell them about NSF?
• How do you decide whether to draw labs for renal insufficiency? Who receives contrast, what kind, and in what dose?
• Can gadolinium be given safely to infants and children?
• Should the dose of gadolinium be reduced in infants and children?
• Can gadolinium be given to lactating women?
• Can gadolinium be given to pregnant women?
• Does gadolinium accumulate in tissues after repeated doses?
• Does gadolinium retention in the body cause symptoms?

      Paramagnetism: Hemorrhage»

• The appearance of hemorrhage on MRI seems very complicated. Can you simplify it?
• What are the different forms of hemoglobin and why do they have different magnetic properties?
  
• What does fresh (hyperacute) hemorrhage look like on MRI?
  
• Why does acute hemorrhage become dark on T2-weighted images?
  
• Why is methemoglobin bright on T1-weighted images?
  
• If deoxy-Hb loses an electron to form met-Hb, why is met-Hb more paramagnetic?
  
• Why do the imaging properties change depending on whether methemoglobin is intracellular vs extracellular?
  
• Can you explain the appearance of old/chronic hematomas on MRI?
  
• What happens after the met-Hb stage and how do these later degradation products affect the MR signal?
  
• What is ferritin? How is it different from hemosiderin?
  
• How does the appearance of subarachnoid hemorrhage differ from parenchymal hemorrhage on MRI?

Cardiovascular and MRA

      Flow Effects in MR»

• How is blood flow measured in a vessel?
  
• What are the usual velocities of blood found in the human vascular system? 
  
• What is the difference between laminar flow, turbulent flow, and vortex flow?  
  
• How can you predict whether a certain vessel will be bright or dark on an MR image?
• What are time-of-flight effects?  
  
• What are spin-phase effects? 
• Dr. Elster, I've been told you don't like or use the term 'flow void'. Why is that?
  
• Why do gradient echo (GRE) sequences accentuate the signals from flowing blood or CSF?  
  
• How do you distinguish slow flow from thrombus on MR images?  
  
• Can you explain even-echo rephasing? 
  
• Please explain how flow compensation (gradient-moment nulling) software works.
  
• Why does the refocused signal from flowing blood often does not line up with the vessel on MR imaging?   

      MR Angiography: Part I»

• How do you create an MR angiogram?
• Why would you want to choose dark blood over bright blood for MRA? Can't you just invert the bright blood image on a monitor and get the same effect?  
  
• How does time-of-flight MRA work?
• You mentioned that TOF MRA could be performed in either 2D or 3D mode. Which should I use?
• How do you choose TR, TE, and flip angle for a TOF MRA sequence?
• How do magnetization transfer pulses improve MRA?
• How does varying the flip angle improve TOF MR angiography? 
  
• What is MOTSA?
• The signal from fat sometimes obscures vessels on TOF MRA. Can fat suppression be used to improve image quality?
• What are the major TOF MR artifacts should we know about?
• How does phase-contrast MR angiography work? 
• What is VENC and how do you set it correctly?
• How can phase contrast techniques be used to measure flow?
• How accurate are MR methods to measure flow? What are the artifacts and pitfalls?     
  

      MR Angiography: Part II»

• What is gated 3D fast spin echo MRA? When and where would I want to use it? 
• What are the steps in performing a gated 3D- FSE MRA study? What parameters are used? 
• What is SSFP MRA and how does it work? When would I want to use this technique?  
• How do inflow-enhanced SSFP MRA sequences work? Where do you place the saturation bands?  
• What is arterial spin labeling (ASL) and how does it improve MRA?
  
• What other MRA methods are out there, and what do you see on the future?
• How is contrast-enhanced MRA performed?  
  
• How do you compute the arrival of contrast in a vessel to know when to start the MR acquisition?  
  
• I know there are different view ordering options for MRA, such as linear and elliptical centric. What do these mean, and when is each used?
  
• What is bolus-chasing and how is it used for peripheral MR angiography?
  
• What are TRICKS and TWIST? How do these differ from "regular" MRA? 
• What artifacts on contrast-MRA should we know about?   

      Cardiac MRI: Part I (Intro/Anatomy)»

• Our cardiac MRI binder contains over a dozen different protocols. Can you make sense of these?
• Are there any special measures needed in preparing a patient for a cardiac MRI exam?
  
• We often have trouble getting a clean EKG signal for cardiac gating. Any helpful hints?
  
• I've heard the magnetic field changes the EKG. Why does this occur? It it dangerous? 
• Is cardiac gating the same as triggering? 
• How do you set the various parameters for a cardiac gated study, such as repetition time (TR), trigger delay, and trigger window?
• How can navigators track heart position if placed on the diaphragm?
• When is double inversion recovery used for cardiac imaging? How does it work? 
• Why go to the trouble of using a double IR method to suppress blood? Couldn't blood be suppressed with a single carefully selected TI value?
• Isn't double inversion recovery enough? Why would you want to do triple IR?  
• How do you interpret those colorful circular plots of cardiac function? 
• How is coronary artery MRA performed? Is it of any use?          

      Cardiac MRI: Part II (Function)»

• How do they make those movies of the beating heart?
• How do you choose imaging parameters for a cine cardiac study? 
• What do you do if the patient can't hold her breath or has multiple intruding arrhythmias?
  
• How is ejection fraction computed using cine MRI?
  
• What is SPAMM?
  
• How does a myocardial perfusion study MRI work? Why would you want to do one?
  
• What is the best technique for "first- pass" perfusion imaging?
  
• Can myocardial perfusion be accurately quantified?
  
• What produces the dark rim artifact on cardiac perfusion MRI?

      Cardiac MRI: Part III (Viability)»

• What causes myocardial enhancement? Is delayed enhancement specific for infarction?
• What is the best way to see myocardial enhancement?
  
• What is the difference between magnitude and phase-sensitive IR for detecting myocardial enhancement?
  
• How is cardiac T1 mapping performed? When is it useful?
  
• How and why is T2*-myocardial mapping performed?
  
• How are T2-weighted imaging and mapping used for cardiac diagnosis?
  
• Several drugs are available to perform cardiac stress. Which one should I use?
  
• What risks and complications should patients be informed about when undergoing stress perfusion testing?

Functional Imaging

      Perfusion I: Intro and DSC»

• How is perfusion defined and measured?
• How are parameters like BF, BV, and MTT defined and used in perfusion imaging?
• What are the differences between DSC, DCE and ASL perfusion methods used in MRI?
• How do you perform a DSC perfusion study?
• If gadolinium contrast is used to increase signal intensity on routine MR images, why does it decrease signal on DSC perfusion images?
• What about areas of contrast enhancement? Surely some T1 effects of gadolinium are present there...
• Why doesn't the DSC curve return to its baseline after passage of the contrast bolus?
• What is the negative enhancement integral and how is it calculated?
• Is it possible to quantify the actual concentration of Gd from its signal in a DSC study?
• What is the arterial input function (AIF) and why do you need to measure it?
• How is the arterial input function used to extract more quantitative flow information from the DSC data?    

      Perfusion II: DCE»

• What is DCE imaging and how does it differ from DSC imaging?
• What pulse sequences are used to perform a DCE study?
  
• How do you evaluate the information obtained from a DCE imaging study?
  
• Does breast DCE require any special techniques?
  
• How is the concentration of gadolinium in blood and tissue determined from the DCE signal?
  
• What quantitative parameters can be extracted from the DCE data?
  
• How do calculated DCE parameters relate to patterns of enhancement we see on clinical images?
  
• Is K^trans the same as permeability?
  
• When might quantitative DCE imaging be useful? Can you give some examples? 

      Perfusion III: ASL»

• What is arterial spin labeling (ASL) and how does it work? 
• Can you briefly explain the difference between the various ASL methods? Which is the best?
  
• What is CASL?
  
• What is PASL and how does it differ from CASL?
  
• What is pCASL and how does it differ from CASL and PASL?
  
• How should imaging parameters be chosen to optimize an ASL acquisition?
  
• What ASL artifacts should we know about?
  
• Can gadolinium be given in conjunction with ASL?
  
• I have seen some ASL maps with vascular territories colored in. How are these produced?
  
• How are ASL methods able to quantify blood flow?
  

      Functional MRI/BOLD: Part I»

• How is image contrast produced by BOLD fMRI?
• How does fMRI work?
• How is image contrast produced by BOLD fMRI?
• Why does the BOLD signal increase during activation? It seems like it should decrease since more oxygen is being used up. 
• Does the BOLD response result from the firing of nerve cells?  
• What is the best pulse sequence to use for BOLD fMRI?
• How do you design a BOLD/fMRI study?
• ​Why do you have to do an "on-off" comparison? Why not just measure the absolute BOLD signal instead?
• What is the best way to identify the motor cortex using fMRI?
• What about fMRI of the visual system?  
• ​What paradigms do you use to test language function prior to surgery?

      Functional MRI/BOLD: Part II»

• How is fMRI data processed and analyzed?
• What is the best software for processing fMRI data?
• What are the steps for preprocessing fMRI data?
• What is the difference between co-registration and normalization? How are these performed?
• How do you statistically analyze fMRI data?
• I don't really understand how GLM works. Can you explain it more completely?
• How are those activation "blobs" on an fMRI image created, and what exactly do they represent?
• We often see areas of fMRI activation outside the brain itself. Why do these occur and what can be done to correct them?
• What is meant by resting state fMRI? How is it used?
• How do you process and analyze resting state fMRI data?
• How is network theory used to analyze fMRI data?
• Many researchers are doing fMRI at 7T and higher, so there must be some advantages. What are they?
• Can fMRI read your mind?
• Dr. Elster, I understand you are somewhat skeptical about certain aspects of fMRI. Can you explain?

MR Spectroscopy

      MRS I: Basics»

• What's the difference between MRI and MRS? 
• How do you obtain spectra instead of images on an MR scanner?  
• What is meant by a chemical shift? 
• How are proton chemical shifts measured on the δ scale?  
• Why does the spectroscopy scale run backwards?  
• How can you predict the chemical shift of hydrogen with a molecule?
• Why are some spectral peaks taller than others? Why are some wide while others are narrow?  
• Why do some spectra split into smaller peaks while others do not? 
• If frequency-encoding cannot be used to determine spatial position, how do you localize an MRS signal?  
• How do you choose between a single and multi-voxel technique?  
• Can you explain how PRESS works and why is it the most popular MRS method?  
• How does the STEAM method for MR Spectroscopy work and when should it be used? 
• How does the ISIS technique work and why is it preferred over PRESS for phosphorus spectroscopy?  
• How is chemical shift imaging performed?  

      MRS II: Clinical ¹H Applications»

• How do you perform a "standard" MRS exam of the brain?  
• Why and how do you suppress water signal in MRS?  
• How and why is fat suppression performed in an MRS study?
• What do the peaks seen in routine brain MRS represent?  
• How do you pick various imaging parameters (TR, TE, etc) for a brain MRS study?  
• What is Hunter's angle? What does it mean if the peaks don't line up?  
• Why does the lactate peak flip upside down? None of the other peaks do. 
• How are those color overlay maps of metabolites produced? 
• Can MRS peaks be quantified? How accurate is this?  
• How do you perform breast spectroscopy? What do the peaks mean? 
• Does gadolinium contrast affect MR spectral lines?  
• How do you perform prostate MRS? Are endorectal coils required?
• How do you interpret spectra from the prostate?  
• What about spectroscopy of the musculoskeletal system?  
• How is MRS used to evaluate diseases of the liver?  
• What MRS artifacts should we know about?  

      MRS III: Multi-nuclear»

• What nuclei besides hydrogen can be investigated with MRS?  
• After hydrogen, why is phosphorus the most widely used nucleus for spectroscopy? 
• What must you do differently to perform ³¹P- instead of ¹H-spectroscopy? 
• What peaks are seen in the ³¹P spectrum and what do they mean?
• How do ³¹P spectra differ among the various organs?  
• You made reference to the use of ³¹PMRS to measure cellular metabolism. How does this work?  
• What is decoupling? Is it required for phosphorus spectroscopy?  
• What is NOE? How and when should it be used for phosphorus MRS?
• What is the status of ¹ ³C spectroscopy? I haven't seen much about this at all.
• Can't sodium also be used for spectroscopy?  
• Is it true that xenon gas can be seen on MRI scans? If so, how is it used?  

MR Artifacts

      Tissue-related Artifacts»

• What is a chemical-shift artifact?
• Doesn't the chemical shift between water and fat protons also result in a phase shift between them? If this is so, then why aren't chemical shift artifacts seen in the phase-encode direction also?
• What can you do to eliminate or reduce the chemical shift artifact?
• What is a chemical shift artifact of the second kind?
• What is meant by in-phase vs out-of-phase imaging?
• I've noticed that T1-FLAIR images may show "India ink" outlines. Is this also a chemical shift artifact?
• What are susceptibility artifacts?
• We recently purchased a metal artifact reduction software for one of our scanners. How does that work?
• What is the dielectric effect and how does it produce artifacts in MRI?
• How do you reduce dielectric artifacts? How good are dielectric pads at solving this problem?

      Motion-related Artifacts»

• Why do motion artifacts often form into discrete ghosts?
• Why are motion artifacts propagated in the phase-encode direction instead of the frequency-encode direction?
• How can motion artifacts be reduced or eliminated?
• How do saturation pulses work?
• How are cardiac and respiratory gating performed?
• What is respiratory compensation? How does this differ from respiratory gating?
• What are navigator echoes and how do they reduce motion artifacts?
• How does PROPELLER reduce motion artifacts?

      Technique-related Artifacts»

• What is meant by "partial voluming"?
• Why are there dark bands over the lumbar spine?
• What is aliasing?
• Why does the phase wrap-around artifact occur?
• How do I get rid of phase wrap-around artifacts?
• How does phase oversampling eliminate the wrap-around artifact?
• Why aren't wrap-around artifacts seen in the frequency-encode direction, too?
• What about wrap-around artifacts on radial or spiral imaging? it seems like they should always be present because phase-encode goes in every direction.
• What is a Gibbs artifact?
• On EPI we commonly see three overlapping images. It looks somewhat like a phase wraparound artifact. What is causing this?
• We intermittently see zipper-like artifacts in our images. What causes them?
• Are there any other data-related artifacts that we should be aware of?
• What is surface coil flare? What can be done about it?
• What are the major TOF MR artifacts should we know about?
• What artifacts on contrast-enhanced MRA should we know about?