Artifact Know How Part II

This post is continuing the post about Artifact in MR.

Partial Blurring and Double Object



As you can see in image above, the image on far left show us these patient looks like to have 2 spinal cord, while image next to it show us image blur on about 3/4 part of the image.  Why these condition happens ?
These condition may occur if :

  • Patient movement in the middle of the measurement
  • Patient coughing while measurement is taken.

Obviously these artifacts are patient related artifact.  And like any patient related artifact, these artifact can be avoided by :

  • A proper communication prior to the exam, this include what will happen and what they should do or don't during the examination.  It's always a good practice to let patient adapt to the machine before we perform the series of measurement.  This 5 minute spent before the examination may save more time longer than that to repeat the series after.
  • Give a break between sequence and communicate to patient what has done and what will done. Ask them to keep still while the noise sound heard.  This little practice may help patient to be more relaxed and calm
  • If this happen, talk to your patient.  Ask what they feel, whether he/she can keep still any longer  and repeat the sequence.

Blurred of Respiratory Motion






During abdominal or thorax MR, almost all sequence require respiratory control in order to create a sharp visible images.  There we need Gradient echo sequence with single or multiple Breath Hold command to produce that kind of image. As you may know the Gradient Echo offer you a fast measurement, much more faster than  traditional spin echo sequences.  But sometimes some sequence just can't performed with GRE sequences or the patient just can't hold their breath due to their sickness or condition, there this image like above may occur.  In order to create a clear sharp images of abdomen, these may works :
  • Train your patient prior to the exam, see whether they ca hold their breath or how long they can hold their breath
  • Use a fast Sequence, GRE Type sequences with breath hold command.  as eample FLASH may work for T1 weighted or a HASTE sequence for T2 Weighted.
  • Use concatenation to break your multiple breath hold examination to meet your patient breath hold capability
  • For patients that can't hold breath use respiratory Belt / Respiratory Trigger or Sequence with free breath capability. (In Siemens System named as 2D/3D PACE).

False Lesion due to Swallowing

Place attention to 2 images above.  The left images show us  some spots of hyper intense image inside the spinal cord while the right side -- which is the same patient -- is not.  While this is very tricky images, image on left side that is show us the "lesion" is measured during the patient swallow the saliva.  Why I said tricky, because the hyper intense may occur due to : true lesion or swallowing artifact.
This kind of image may lead you and the doctor to misinterpretation or the unnecessary injection of Gad. therefore to ensure this not occur or to minimize the risk of the incident these may work :
  • Communicate with your patient that the examination require then to not swallowing during the measurement, which is marked by noisy sound.  Therefore during the noisy sound the must hold they self from swallowing anything
  • Give a break during measurement to give them chance to swallow.  Instruct them to not swallow before you begin the measurement
  • If happen, assess all your images.  Lesion should appear in all images series (T1/T2/Fat saturation), if only one sequence show you this, repeat the sequence for confirmation  
Susceptibility Artifact
Susceptibility roughly mean as the characteristic of material to be magnetized by external field.  For any material which poses high susceptibility it will produce local magnetic field during the MR exam, thus will decrease the signal intensity around it.  Metal is highly susceptible material. So, any metal present in area or near area of the FoV may result in susceptibility artifact as below :

 From Top Left, Clock wise :
Orthopedic Implant, give you no signal area due to high signal decrease in area around the implant followed by bright area produced by high signal intensity due to the decreased high local magnetic field around the metal related to its distance to the metal object.
Permanent dental implant, give a streak of high signal intensity and distorted face with no signal area in location of implant
Hair pin. Hair pin may result in distorted skull with appearance of high signal intensity artifact
Dental Wires. Typical images showing a horse shoe like artifact on brain may occur by a dental wires on upper teeth.
To avoid these kind of artifact, these may works :

  • Ask patient to remove any metal contained accessories or implant that can be removed.
  • Screening the patient with metal detector before entering the room.  Some metal accessories might be become so usual or daily habit  to the patient so they forgot to removed it
  • for any implant that cannot be removed use TSE sequence with long Echo Train Length to reduce the susceptibility effect.  Avoid using GRE sequence, since this type of sequence is highly sensitive to susceptibility.

 Zipper Artifact







These type of artifact occur because RF wave Interfere the system.  This may happen from several source, listed but not limited to below :
  • Medical device that is not RF shielded placed inside the magnet room.  AS example like Power Injector and Patient monitor or external triggering device
  • Blinking light bulbs
  • Examination Room Door not tightly closed
  • Drilling work near magnet room

To avoid this artifacts, these may help :
  • Ensure all device to be placed in Magnet room is RF Wave shielded, these device usually made specifically for MRI room.  These devices must shielded from it cables to the device it self.
  • Turn off the lamp when the examination about to begin to avoid blinking lamp happen during the examination
  • Close the examination room door tightly, all MR system at present usually give a warning messages if the door not tightly closed.
  • Any building / structural work like drilling, hammering near the MR room must be performed out the MR service hours whenever possible
Those all a little about MR artifact,  There're still many type of artifact may occur in MR examination. YOu can google it  and find hundred source of  articles provide you with the information. These books may provide you with more information 


Sociable

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