AMSM – Gallery of Artifacts

Magnetic Resonance Spectroscopy and Methodology - Department of Clinical Research - University Bern/Switzerland

 

This gallery has been initiated by R.Kreis, Ph.D. based on his review article in NMR in Biomedicine

 

A Gallery of Artifacts in Clinical Magnetic Resonance Spectroscopy


Artifacts are not at all conspicuous in clinical Magnetic Resonance Spectroscopy (MRS) and can easily be taken for true, interpretable features. The user of clinical MRS needs some technical background knowledge, good technical tools, but also an experienced eye, since error and artifact detection are not built into any commercial system. These pages aim to increase interest in issues of spectral quality and quality assessment by providing a sample gallery of artifacts, hopefully raising awareness for potential pitfalls in MRS. The initially presented examples have been assembled by the MR Team of University Berne, Switzerland. Some have been published in NMR Biomed 2004 (17, in press). We invite users of clinical MRS to provide further examples of artifacts and pitfalls that can be added to this Gallery. Please submit artwork as powerpoint or jpg files and some explanatory text to MRS-artifacts@dkf.unibe.ch. (Please state whether institution where artifact was recorded and your identity should be acknowledged/revealed.)

 

 

(This web site is still under construction, please bear with us)

 


Gallery of artifacts in MRS

Patient-related Artifacts: Movements/Motion:

      Gross bulk motion

                         Patient leaves scanner

                         Patient tilts head

                         Intermittent head movements

      Physiologic motion

      Metallic implants, dental braces

Prescan Failure

      ROI shape

      ROI shape and B1 miscalibration

      Water suppression

      Inadequate shim

Problems with acquisition software (localization sequence)

      Outer volume signal bleed (single voxel MRS):

                         ROI shape

                         Lipids from ROI boundary

                         Out of phase lipid signals

      Pointspread function (PSF) in spectroscopic imaging (SI):

                         PSF in classical SI

                         Effect of zero-filling on the PSF

      Outer volume ghosts:

                         Spurious echo

                         Identification of ghost using fitting residuals

      Chemical shift artifact:

                         Typical order of magnitude

                         Effect on hemispheric comparison

      Gradient misadjustment: (shifted echoes )

Postprocessing, Model Fitting

      Inadequate fitting model

      Wrong assignments

Hardware problems:

      Eddy currents

      External source of RF

                         Mimics bacterial infection

                         Mimics neurodegeneration

      Faulty analog to digital conversion (ADC)

                         case 1

                         case 2

      Non-linear RF amplifier

                         Effect on quantitation with reciprocity principle

                         Leading to wrong flip angle setting

      Hardware replacement

                         Inappropriate use of reciprocity

      Gradient vibration

                         Sidebands in MRS without water suppression

      Analogue filter

      2nd channel for heteronuclear MRS