Toward simultaneous PET/MR breast imaging: Systematic evaluation and integration of a radiofrequency breast coil

Aklan, Bassim; Paulus, Daniel H.; Wenkel, Evelyn; Braun, Heinrich; Navalpakkam, Bharath K.; Ziegler, Susanne; Geppert, Christian; Sigmund, Eric E.; Melsaether, Amy N.; Quick, Harald H.

doi:10.1118/1.4788642

Cited by 53 publications

(93 citation statements)

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“…These results demonstrate that disregarding the presence of MR coils leads to substantial regional bias in PET quantification and illustrate the importance of accurate implementation of methodology for MR coil attenuation correction (AC) in simultaneous PET/MR applications. Even though MR coils are invisible in the conventional MR-acquired AC maps, it was shown that coil AC can be successfully implemented using a CT-based template of the coil, which is fused with the MR-based AC-map of the patient [6,9,10]. …”

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A 16-channel MR coil for simultaneous PET/MR imaging in breast cancer

et al. 2014

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ObjectivesTo implement and evaluate a dedicated receive array coil for simultaneous PET/MR in breast cancer. MethodsThe 16 receiver channel coil design was optimized for simultaneous PET/MR. To assess MR performance, signal-to-noise ratio, parallel imaging capability and image quality was evaluated in phantoms, volunteers and patients and compared to clinical standard protocols. For PET evaluation, quantitative 18 F-FDG PET scans of phantoms and seven patients (14 lesions) were compared to scans without coil. In PET image reconstruction, a CT-based template of the coil was combined with the MR-acquired attenuation correction (AC) map of the phantom / patient. ResultsMR image quality was comparable to clinical MR-only exams. PET evaluation in phantoms showed regionally varying SUV underestimation (mean 22%) due to attenuation caused by the coil. This was improved by implementing the CT-based coil template in the AC (< 2% SUV underestimation). Patient data showed that including the coil in the AC increased SUV values in lesions (21% ± 9 %). ConclusionsUsing a dedicated PET/MR breast coil, state-of-the-art MRI was possible. In PET accurate quantification and image homogeneity could be achieved, if a CT-template of this coil was included in the attenuation correction for PET image reconstruction. KeywordsMagnetic Resonance Imaging, Positron-Emission Tomography, Breast cancer, Bilateral breast imaging, RF coil array Key Points• State-of-the-art breast MRI using a dedicated PET/MR breast coil is feasible.• A multi-channel design facilitates shorter MR acquisition times through parallel imaging.• The MR coil inside a simultaneous PET/MR system causes PET photon attenuation.• Including a coil CT-template in PET image reconstruction, accurate quantification is recovered. [2][3][4]. Although successfully applied in many oncologic applications, simultaneous PET/MR in breast cancer has so far been delayed due to the need for a dedicated breast coil, which enables prone positioning and achieves high image quality, as a precondition for state-of-the-art breast MRI [5]. However, the presence of MR related hardware, such as a breast coil, in the PET field-of-view (FOV) causes significant attenuation of the 511 keV annihilation photons, therefore hampering PET image quality [6]. Studies found, that the presence of MR head coils, which contain a substantial amount of plastic housing material, lead to 13-19% underestimation of PET activity concentration, if not accounted for during image reconstruction [7]. The attenuation effects for "lighter" or more "transparent" MR surface coils were only 4% overall, but up to 10-15% closer to the coil surface [8]. These results demonstrate that disregarding the presence of MR coils leads to substantial regional bias in PET quantification and illustrate the importance of accurate implementation of methodology for MR coil attenuation correction (AC) in simultaneous PET/MR applications. Even though MR coils are invisible in the conventional MR-acquired AC maps, it was shown that coil A...

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A 16-channel MR coil for simultaneous PET/MR imaging in breast cancer

et al. 2014

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“…For accurate quantification, attenuation maps of the coil elements in the FOV should be estimated and used during reconstruction. Because of a loss in counts, the global activity concentration will be underestimated when the coil is not accounted for in the attenuation correction (AC), but errors will be especially prevalent near the coil (33)(34)(35). The problem with the coils and other objects in the FOV, such as the bed, is that they provide no MR signal although they attenuate radiation.…”

Section: Mrmentioning

confidence: 99%

“…The problem with the coils and other objects in the FOV, such as the bed, is that they provide no MR signal although they attenuate radiation. Coils with a fixed position can easily be measured beforehand, for example, with CT, and used as a template in the AC (34,36). In a similar manner, the bed can be included in the AC.…”

Section: Mrmentioning

confidence: 99%

“…However, coil placement should be fairly accurate because small misalignments could already create image artifacts and incorrect quantification (33,36). Additionally, the CT scan of the coils may have artifacts due to the metal components, which in turn can affect the PET images (34). An even more difficult challenge is attenuation due to flexible coils that can be placed in variable positions and orientations.…”

Section: Mrmentioning

confidence: 99%

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Principles of PET/MR Imaging

et al. 2014

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Hybrid PET/MR systems have rapidly progressed from the prototype stage to systems that are increasingly being used in the clinics. This review provides an overview of developments in hybrid PET/MR systems and summarizes the current state of the art in PET/MR instrumentation, correction techniques, and data analysis. The strong magnetic field requires considerable changes in the manner by which PET images are acquired and has led, among others, to the development of new PET detectors, such as silicon photomultipliers. During more than a decade of active PET/MR development, several system designs have been described. The technical background of combined PET/MR systems is explained and related challenges are discussed. The necessity for PET attenuation correction required new methods based on MR data. Therefore, an overview of recent developments in this field is provided. Furthermore, MR-based motion correction techniques for PET are discussed, as integrated PET/MR systems provide a platform for measuring motion with high temporal resolution without additional instrumentation. The MR component in PET/MR systems can provide functional information about disease processes or brain function alongside anatomic images. Against this background, we point out new opportunities for data analysis in this new field of multimodal molecular imaging.

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“…Using simulations, the authors demonstrated that this approach reduces the interframe registration error between activity and attenuation maps. The attenuation of fixed objects, such as patient bed, body, and rigid coils (i.e., head/neck, spine, and torso) can be measured using transmission sources ( 68 Ge or 137 Cs) 119 or CT scans 120 and incorporated into attenuation maps as templates. The patient table and coil templates generated from transmission scans are more accurate than those generated from CT scans owing to the lack of streaking artifacts caused by high-density metallic components.…”

Section: B5 Emission-based Attenuation/motion Estimationmentioning

confidence: 99%

Vision 20/20: Magnetic resonance imaging‐guided attenuation correction in PET/MRI: Challenges, solutions, and opportunities

2016

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Attenuation correction is an essential component of the long chain of data correction techniques required to achieve the full potential of quantitative positron emission tomography (PET) imaging. The development of combined PET/magnetic resonance imaging (MRI) systems mandated the widespread interest in developing novel strategies for deriving accurate attenuation maps with the aim to improve the quantitative accuracy of these emerging hybrid imaging systems. The attenuation map in PET/MRI should ideally be derived from anatomical MR images; however, MRI intensities reflect proton density and relaxation time properties of biological tissues rather than their electron density and photon attenuation properties. Therefore, in contrast to PET/computed tomography, there is a lack of standardized global mapping between the intensities of MRI signal and linear attenuation coefficients at 511 keV. Moreover, in standard MRI sequences, bones and lung tissues do not produce measurable signals owing to their low proton density and short transverse relaxation times. MR images are also inevitably subject to artifacts that degrade their quality, thus compromising their applicability for the task of attenuation correction in PET/MRI. MRI-guided attenuation correction strategies can be classified in three broad categories: (i) segmentation-based approaches, (ii) atlasregistration and machine learning methods, and (iii) emission/transmission-based approaches. This paper summarizes past and current state-of-the-art developments and latest advances in PET/MRI attenuation correction. The advantages and drawbacks of each approach for addressing the challenges of MR-based attenuation correction are comprehensively described. The opportunities brought by both MRI and PET imaging modalities for deriving accurate attenuation maps and improving PET quantification will be elaborated. Future prospects and potential clinical applications of these techniques and their integration in commercial systems will also be discussed. C 2016 American Association of Physicists in Medicine. [http://dx

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Toward simultaneous PET/MR breast imaging: Systematic evaluation and integration of a radiofrequency breast coil

Abstract: The successful integration of a four-channel RF breast coil with a defined table position together with the CT-based μ-maps provides a technical basis for future clinical PET/MR breast imaging applications.

Cited by 53 publications

References 20 publications

A 16-channel MR coil for simultaneous PET/MR imaging in breast cancer

A 16-channel MR coil for simultaneous PET/MR imaging in breast cancer

Principles of PET/MR Imaging

Vision 20/20: Magnetic resonance imaging‐guided attenuation correction in PET/MRI: Challenges, solutions, and opportunities

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