Wideband Self-Grounded Bow-Tie Antenna for Thermal MR.

Abstract

The objective of this study was the design, implementation, evaluation and application of a compact wideband self-grounded bow-tie (SGBT) radiofrequency (RF) antenna building block that supports anatomical proton ( H) MRI, fluorine ( F) MRI, MR thermometry and broadband thermal intervention integrated in a whole-body 7.0 T system. Design considerations and optimizations were conducted with numerical electromagnetic field (EMF) simulations to facilitate a broadband thermal intervention frequency of the RF antenna building block. RF transmission (B ) field efficiency and specific absorption rate (SAR) were obtained in a phantom, and the thigh of human voxel models (Ella, Duke) for H and F MRI at 7.0 T. B efficiency simulations were validated with actual flip-angle imaging measurements. The feasibility of thermal intervention was examined by temperature simulations (f = 300, 400 and 500 MHz) in a phantom. The RF heating intervention (P = 100 W, t = 120 seconds) was validated experimentally using the proton resonance shift method and fiberoptic probes for temperature monitoring. The applicability of the SGBT RF antenna building block for in vivo H and F MRI was demonstrated for the thigh and forearm of a healthy volunteer. The SGBT RF antenna building block facilitated F and H MRI at 7.0 T as well as broadband thermal intervention (234-561 MHz). For the thigh of the human voxel models, a B efficiency ≥11.8 μT/√kW was achieved at a depth of 50 mm. Temperature simulations and heating experiments in a phantom demonstrated a temperature increase ΔT >7 K at a depth of 10 mm. The compact SGBT antenna building block provides technology for the design of integrated high-density RF applicators and for the study of the role of temperature in (patho-) physiological processes by adding a thermal intervention dimension to an MRI device (Thermal MR).

AI evidence extraction

Main findings

A compact wideband self-grounded bow-tie RF antenna building block was designed and evaluated for 7.0 T MRI and broadband thermal intervention. In thigh voxel models, B1 efficiency was reported as ≥11.8 μT/√kW at 50 mm depth, and phantom simulations/experiments showed a temperature increase ΔT >7 K at 10 mm depth during RF heating (P = 100 W, t = 120 s) across intervention frequencies (reported broadband 234–561 MHz; simulations at 300/400/500 MHz).

Outcomes measured

• RF transmission (B1) field efficiency
• Specific absorption rate (SAR) (phantom and simulations)
• Temperature increase (ΔT) during RF heating intervention
• Feasibility of proton (1H) MRI and fluorine (19F) MRI at 7.0 T
• Validation of flip-angle imaging measurements
• MR thermometry (proton resonance shift) and fiberoptic temperature monitoring

Limitations

• Sample size for in vivo demonstration not specified beyond a single healthy volunteer
• Temperature increase results reported for phantom (not stated for in vivo)
• SAR values are mentioned as obtained but not reported in the abstract
• Frequencies are given as ranges/selected values; no single primary exposure frequency specified

{
    "study_type": "engineering",
    "exposure": {
        "band": "RF",
        "source": "MRI (7.0 T) RF antenna / thermal intervention",
        "frequency_mhz": null,
        "sar_wkg": null,
        "duration": "t = 120 seconds (heating intervention)"
    },
    "population": "Healthy volunteer (thigh and forearm imaging); human voxel models (Ella, Duke) and phantom experiments",
    "sample_size": 1,
    "outcomes": [
        "RF transmission (B1) field efficiency",
        "Specific absorption rate (SAR) (phantom and simulations)",
        "Temperature increase (ΔT) during RF heating intervention",
        "Feasibility of proton (1H) MRI and fluorine (19F) MRI at 7.0 T",
        "Validation of flip-angle imaging measurements",
        "MR thermometry (proton resonance shift) and fiberoptic temperature monitoring"
    ],
    "main_findings": "A compact wideband self-grounded bow-tie RF antenna building block was designed and evaluated for 7.0 T MRI and broadband thermal intervention. In thigh voxel models, B1 efficiency was reported as ≥11.8 μT/√kW at 50 mm depth, and phantom simulations/experiments showed a temperature increase ΔT >7 K at 10 mm depth during RF heating (P = 100 W, t = 120 s) across intervention frequencies (reported broadband 234–561 MHz; simulations at 300/400/500 MHz).",
    "effect_direction": "unclear",
    "limitations": [
        "Sample size for in vivo demonstration not specified beyond a single healthy volunteer",
        "Temperature increase results reported for phantom (not stated for in vivo)",
        "SAR values are mentioned as obtained but not reported in the abstract",
        "Frequencies are given as ranges/selected values; no single primary exposure frequency specified"
    ],
    "evidence_strength": "insufficient",
    "confidence": 0.7399999999999999911182158029987476766109466552734375,
    "peer_reviewed_likely": "yes",
    "keywords": [
        "self-grounded bow-tie antenna",
        "wideband RF antenna",
        "7.0 T MRI",
        "1H MRI",
        "19F MRI",
        "MR thermometry",
        "thermal intervention",
        "electromagnetic field simulations",
        "B1 efficiency",
        "SAR",
        "phantom",
        "voxel models"
    ],
    "suggested_hubs": []
}

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