In vivo quantification of contrast agent concentration using the induced magnetic field for time-resolved arterial input function measurement with MRI.

Medical physics · 2008 · Unclear · Insufficient evidence

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UnclearInsufficient evidencePaper 2825

The study demonstrates feasibility of determining an arterial input function from susceptibility-induced magnetic field changes during an intravenous bolus. In 14 subjects, dynamically measured gadolinium concentration curves and derived flow rate estimates w…

Study snapshot

PublicationMedical physics · 2008

Study typeother

Reported directionUnclear

Evidence ratingInsufficient

Abstract

For pharmacokinetic modeling of tissue physiology, there is great interest in measuring the arterial input function (AIF) from dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) using paramagnetic contrast agents. Due to relaxation effects, the measured signal is a nonlinear function of the injected contrast agent concentration and depends on sequence parameters, system calibration, and time-of-flight effects, making it difficult to accurately measure the AIF during the first pass. Paramagnetic contrast agents also affect susceptibility and modify the magnetic field in proportion to their concentration. This information is contained in the MR signal phase which is discarded in a typical image reconstruction. However, quantifying AIF through contrast agent susceptibility induced phase changes is made difficult by the fact that the induced magnetic field is nonlocal and depends upon the contrast agent spatial distribution and thus on organ and vessel shapes. In this article, the contrast agent susceptibility was quantified through inversion of magnetic field shifts using a piece-wise constant model. Its feasibility is demonstrated by a determination of the AIF from the susceptibility-induced field changes of an intravenous bolus. After in vitro validation, a time-resolved two-dimensional (2D) gradient echo scan, triggered to diastole, was performed in vivo on the aortic arch during a bolus injection of 0.1 mmol/kg Gd-DTPA. An approximate geometrical model of the aortic arch constructed from the magnitude images was used to calculate the spatial variation of the field associated with the bolus. In 14 subjects, Gd concentration curves were measured dynamically (one measurement per heart beat) and indirectly validated by independent 2D cine phase contrast flow rate measurements. Flow rate measurements using indicator conservation with this novel quantitative susceptibility imaging technique were found to be in good agreement with those obtained from the cine phase contrast measurements in all subjects. Contrary to techniques that rely on intensity, the accuracy of this signal phase based method is insensitive to factors influencing signal intensity such as flip angle, coil sensitivity, relaxation changes, and time-of-flight effects extending the range of pulse sequences and contrast doses for which quantitative DCE-MRI can be applied.

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AI evidence extraction

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Study typeother

Effect directionunclear

PopulationIn vivo human subjects undergoing MRI during intravenous bolus injection of Gd-DTPA; aortic arch imaging

Sample size14

ExposureNot supplied

Evidence strengthInsufficientConfidence: 74% · Peer reviewed: yes

Main findings

Outcomes measured

Feasibility of quantifying contrast agent susceptibility via inversion of magnetic field shifts
Time-resolved arterial input function (AIF) / gadolinium concentration curves (one per heartbeat)
Agreement of flow rate estimates (indicator conservation) with 2D cine phase contrast flow measurements

Limitations

Induced magnetic field is nonlocal and depends on contrast agent spatial distribution and organ/vessel shapes
Uses an approximate geometrical model of the aortic arch constructed from magnitude images
Validation described as indirect via independent cine phase contrast flow measurements
In vitro validation mentioned but details not provided in the abstract

View raw extracted JSON

{
  "study_type": "other",
  "exposure": {
    "band": null,
    "source": "MRI",
    "frequency_mhz": null,
    "sar_wkg": null,
    "duration": null
  },
  "population": "In vivo human subjects undergoing MRI during intravenous bolus injection of Gd-DTPA; aortic arch imaging",
  "sample_size": 14,
  "outcomes": [
    "Feasibility of quantifying contrast agent susceptibility via inversion of magnetic field shifts",
    "Time-resolved arterial input function (AIF) / gadolinium concentration curves (one per heartbeat)",
    "Agreement of flow rate estimates (indicator conservation) with 2D cine phase contrast flow measurements"
  ],
  "main_findings": "The study demonstrates feasibility of determining an arterial input function from susceptibility-induced magnetic field changes during an intravenous bolus. In 14 subjects, dynamically measured gadolinium concentration curves and derived flow rate estimates were in good agreement with independent 2D cine phase contrast flow measurements.",
  "effect_direction": "unclear",
  "limitations": [
    "Induced magnetic field is nonlocal and depends on contrast agent spatial distribution and organ/vessel shapes",
    "Uses an approximate geometrical model of the aortic arch constructed from magnitude images",
    "Validation described as indirect via independent cine phase contrast flow measurements",
    "In vitro validation mentioned but details not provided in the abstract"
  ],
  "evidence_strength": "insufficient",
  "confidence": 0.74,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "MRI",
    "dynamic contrast-enhanced MRI",
    "arterial input function",
    "susceptibility",
    "signal phase",
    "magnetic field shifts",
    "quantitative susceptibility imaging",
    "Gd-DTPA",
    "aortic arch",
    "cine phase contrast"
  ],
  "suggested_hubs": []
}

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AI-extracted fields are generated from the abstract and metadata and may be incomplete or incorrect. This material is for informational purposes and is not medical advice.

Identifiers and source

DOI: 10.1118/1.3002309
PubMed: 19175092

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