Uncertainty and bias in contrast concentration measurements using spoiled gradient echo pulse sequences

Matthias Schabel, Dennis L. Parker

Research output: Contribution to journalArticle

138 Citations (Scopus)

Abstract

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is a widely used technique for assessing tissue physiology. Spoiled gradient echo (SPGR) pulse sequences are one of the most common methods for acquisition of DCE-MRI data, providing high temporal and spatial resolution with strong T 1-weighting. Conversion of SPGR signal to concentration is briefly reviewed, and a new closed-form expression for concentration measurement uncertainty for finite signal-to-noise ratio (SNR) and baseline scan time is derived. This result is applicable to arbitrary concentration-dependent relaxation rate and is valid over the same domain as the theoretical SPGR signal equation. Expressions for the lower and upper bounds on measurable concentration are also derived. The existence of a concentration- and tissue-dependent optimal flip angle that minimizes concentration uncertainty is demonstrated and it is shown that, for clinically relevant pulse sequence parameters, this optimal flip angle is significantly larger than the corresponding Ernst angle. Analysis of three pulse sequences from the DCE-MRI literature shows that optimization of flip angle using the methods discussed here leads to potential improvements of 10-1166% in effective SNR over the 0.5-5.0 mM concentration range with minimal or no loss of measurement accuracy down to 0.1 mM. In vivo data from three study patients provide further support for our theoretical expression for concentration measurement uncertainty, with predicted and experimental estimates agreeing to within ±30%. Equations for concentration bias resulting from biases in flip angle and from pre-contrast relaxation time and contrast relaxivity (both longitudinal and transverse) are also derived in closed-form. The resulting equations show the potential for significant contributions to bias in concentration measurement arising from even relatively small mis-specification of flip angle and/or pre-contrast longitudinal relaxation time, particularly at high contrast concentrations.

Original languageEnglish (US)
Pages (from-to)2345-2373
Number of pages29
JournalPhysics in Medicine and Biology
Volume53
Issue number9
DOIs
StatePublished - May 7 2008
Externally publishedYes

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Uncertainty
echoes
Magnetic resonance
gradients
Magnetic Resonance Imaging
Signal-To-Noise Ratio
pulses
Imaging techniques
Relaxation time
Signal to noise ratio
Tissue
Physiology
magnetic resonance
Specifications
signal to noise ratios
relaxation time
physiology
temporal resolution
specifications
acquisition

ASJC Scopus subject areas

  • Biomedical Engineering
  • Physics and Astronomy (miscellaneous)
  • Radiology Nuclear Medicine and imaging
  • Radiological and Ultrasound Technology

Cite this

Uncertainty and bias in contrast concentration measurements using spoiled gradient echo pulse sequences. / Schabel, Matthias; Parker, Dennis L.

In: Physics in Medicine and Biology, Vol. 53, No. 9, 07.05.2008, p. 2345-2373.

Research output: Contribution to journalArticle

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