Contrast Improvement, Artifacts, and Artifact Reduction

Part of the Medical Radiology book series (MEDRAD)


As discussed in preceding chapters, the basic rationale underlying time-of-flight (TOF) MRA is the utilization of inflow enhancement while compensating for flow-induced phase shifts. For high-resolution studies with isotropic voxels a three-dimensional, or volume acquisition technique is recommended, with the major flow along the slab select direction (Masaryk et al. 1989). While inflow enhancement and resulting vessel contrast is good enough on the side where the vessels enter the volume, the blood signal becomes progressively smaller towards the exit side of the volume. Therefore, the visibility of blood vessels decreases as blood penetrates the volume, as shown in Fig. 4.1. Ultimately, at some point there is no longer any contrast between blood and surrounding stationary tissue. The slab thickness and corresponding vessel coverage cannot be selected on an anatomical basis but rather are determined by contrast issues. The reason for the loss of blood signal is related to the decrease in the spins’ magnetization as they enter the imaging volume and experience the rf pulses in the sequence. This effect is demonstrated in Fig. 4.2 in the form of a numerical simulation. The graph shows the transverse magnetization Mx which corresponds to the signal from the blood as a function of the number of rf pulses. For spins moving at a constant velocity v the number of rf pulses directly corresponds to the spins’ position in the imaging volume when multiplying the velocity G. LAUB, PhD, Siemens AG, Medizinische Technik, Henkestraße 127, 91052 Erlangen, FRG by the pulse repetition time TR and pulse number. Three different curves are shown for different values of the rf excitation pulse.


Flip Angle Magnetization Transfer Artifact Reduction Tone Pulse Contrast Improvement 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Atkinson D, Brant-Zawadzki M, Laub G (1994) Optimization strategies enhance time-of-flight MRA. Radiology 190:890–894PubMedGoogle Scholar
  2. Edelman RR, Manning WJ, Burstein D (1991) Breath-hold MR angiography of human coronary arteries. Radiology 181:641–643PubMedGoogle Scholar
  3. Lewin JS, Laub GA (1991) Intracranial MR angiography: a direct comparison of three time-of-flight techniques. AJNR 12:1133–1139PubMedGoogle Scholar
  4. Lin W, Tkach JA, Haacke EM, Masaryk TJ (1993) Intracranial MR angiography: application of magnetization transfer contrast and fat saturation to short gradient-echo, velocity-compensated sequences. Radiology 186:753–761PubMedGoogle Scholar
  5. Masaryk TJ, Modic MT, Ruggieri PM et al. (1989) Three-dimensional (volume) gradient-echo imaging of the carotid bifurcation: preliminary clinical experience. Radiology 171:801–806PubMedGoogle Scholar
  6. Selby K, Saloner D, Anderson CM et al. (1992) MR angiography with a cardiac-phase-specific acquisition window. J Magn Reson Imaging 2:637–643PubMedCrossRefGoogle Scholar
  7. Tkach JA, Ruggieri PM, Ross JS, Modic MT, Dillinger JJ, Masaryk TJ (1993) Pulse sequence strategies for vascular contrast in Time-of-Flight carotid MR angiography. J Magn Reson Imaging 3:811–820PubMedCrossRefGoogle Scholar
  8. Wolff SD, Balaban RS (1989) Magnetization transfer contrast (MTC) and tissue water proton relaxation in vivo. Magn Reson Med 10:135–144PubMedCrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 1996

Authors and Affiliations

  • G. Laub
    • 1
  1. 1.Medizinische TechnikSiemens AGErlangenGermany

Personalised recommendations