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Optimisation of pseudo-continuous arterial spin labelling (pCASL) MRI in the kidneys
Abstracts, P. McCavana / Physica Medica 32 (2016) 948–959
References 1. BIR. Radiation shielding for diagnostic X-rays, report of a joint BIR/IPEM working party. In: Sutton GG, Williams JR, (editors). London: British Institute of Radiology; 2000. 2. Mathieu KB, Kappadath SC, White RA, et al.. An empirical model of diagnostic X-ray attenuation under narrow-beam geometry. Med Phys 2011;38(8):4546–55. http://dx.doi.org/10.1016/j.ejmp.2016.05.010
Optimisation of pseudo-continuous arterial spin labelling (pCASL) MRI in the kidneys Andrew Malone, James F. Meaney, Andrew Fagan National Centre for Advanced Medical Imaging (CAMI), St James Hospital/TCD, Ireland This paper describes the optimisation of a new MRI technique for evaluating perfusion in the kidney without using an exogenous contrast agents. The kidneys play a pivotal role in the overall functioning of the body by removing waste products and maintaining blood pH and electrolyte balance. Perfusion provides an important biomarker of how well the kidneys are functioning. A pseudo-continuous arterial spin labelling (pCASL) protocol was set-up on a 3T scanner (Achieva, Philips) using a 32-channel detector coil. A single slice was selected positioned obliquely in kidney, with the label plane positioned perpendicularly in the aorta to avoid both the kidneys and the bottom of the heart. A sequence of consecutive breathholds were used to limit bulk kidney motion. 11 healthy volunteers were recruited onto the study after giving ethical consent. The following acquisition and image processing parameters were varied: spatial resolution, use of fat suppression, number of signal averages, and the effect of image registration to remove respiratory motion. The increased SNR of the lowered resolution provided a 36.1% increase in perfusion quantification precision. The use of fat suppression showed a 20.8% increase in SNR and a 31.4% increase in perfusion quantification precision. A minimum of 32–40 signal averages were found to maximise SNR. Finally, it was established that the most accurate perfusion values were obtained using a combination of linear and non-linear registration, yielding a 47.9% increase in perfusion quantification precision. This protocol holds significant promise for future clinical use. http://dx.doi.org/10.1016/j.ejmp.2016.05.011
Error quantification in pharmacokinetic parameters derived from DCE-MRI data using a novel anthropomorphic dynamic prostate phantom Silvin P. Knight a, Jacinta E. Browne b, James F. Meaney a, David S. Smith c, Andrew J. Fagan a a National Centre for Advanced Medical Imaging (CAMI), St James Hospital/TCD, Ireland b School of Physics & Medical Ultrasound Physics and Technology Group, Centre of Industrial Engineering Optics, FOCAS, DIT, Ireland c Institute of Imaging Science/Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, United States Pharmacokinetic (PK) modelling of dynamic contrast enhanced (DCE) MRI data has shown considerable promise in the detection of many cancers, including prostate. However, the clinical implementation of DCE-MRI acquisition protocols suitable for PK modelling has been greatly hindered by the lack of consistency with published PK parameter values, such as the volume-transfer
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constant (Ktrans), with widely varying acquisition protocols and PK modelling approaches adding to the confusion. A novel anthropomorphic dynamic prostate phantom has been developed to address this shortcoming. The device is capable of simultaneously producing two distinct contrast time-intensity curves (CTCs), representative of those observed in DCE-MRI data from healthy and tumorous prostate tissue, in an environment which closely mimics the male pelvic region. CTCs were measured using a custom-built optical scanner, and ‘ground truth’ PK parameter values derived from the data. DCE-MRI data were acquired using a 3T scanner (Achieva, Philips, Netherlands) and a 16-channel phased array detector coil (3D-SPGR, TR/TE = 3.6/1.75 ms, flip = 10°, voxel size = 1.1 1.1 4 mm3, FOV = 224 224 72 mm3, slices = 18). The parallel imaging factor and number of signal averages were varied to give temporal resolutions from 2.3 s to 20.3 s. Ktrans values derived from MR data from the phantom were compared with the ground truth values and were found to differ by 8.1% to 44.6%, with the lowest variance from ground truth values achieved at a temporal resolution of 6.8 s. The phantom provides a model system on which the quantitative validation of new prostate DCE-MRI protocols can be performed, and could contribute to the standardisation of clinical prostate DCE-MRI acquisition protocols. http://dx.doi.org/10.1016/j.ejmp.2016.05.012
Effect of MR contrast agent on quantitative PET during simultaneous PET-MR imaging in cardiology Jim O’Doherty a, Paul Schleyer b a College London, UK b Siemens Healthcare, UK Background MR sequences used in the determination of PET linear attenuation coefficients (LAC) are a common procedure in simultaneous PET-MRI scanning. However during dynamic PET imaging, the introduction of gadolinium-based contrast agents (MRCA) at high concentrations during a dual injection of MRCA and PET radiotracer may cause attenuation effects of the PET radiotracer, and thus errors in quantification of dynamic images. Method We performed simultaneous PET-MR imaging of a phantom using increasing MRCA concentration from 0 to 65 mM (based on MRCA left ventricular concentration in a clinical study) mixed with water and 25 MBq of [18F]-FDG. LAC of the solution was calculated by a mixture rule and compared to measurements from CT images and automated MR LAC segmentation. The effect of increases in the resulting LAC over 0–65 mM was evaluated on a simulated image-derived arterial input function (IDIF) used in the PET kinetic model. Results From 0 to 46 mM, MR segmentation applied a LAC of 0.1 cm 1, and at >46 mM the LAC = 0.0854 cm 1 due to T1 shortening effects. Our results show an increase of only 1.3% in the LAC of the solution over the range of 0–65 mM of MRCA, with an effect on the area under an IDIF of <2%. Thus a minor error is propagated forward to the kinetic model. Conclusion The presence of high MRCA concentration in solution with PET radiotracer produces a minimal effect on PET quantification, provides <2% error to the calculation of perfusion parameters from kinetic models. http://dx.doi.org/10.1016/j.ejmp.2016.05.013
Radiotherapy Session Commissioning of the Intrabeam for Beaumont Hospital Donal Cummins, Pat McCavana St Luke’s Radiation Oncology Network (SLRON), Ireland
References 1. BIR. Radiation shielding for diagnostic X-rays, report of a joint BIR/IPEM working party. In: Sutton GG, Williams JR, (editors). London: British Institute of Radiology; 2000. 2. Mathieu KB, Kappadath SC, White RA, et al.. An empirical model of diagnostic X-ray attenuation under narrow-beam geometry. Med Phys 2011;38(8):4546–55. http://dx.doi.org/10.1016/j.ejmp.2016.05.010
Optimisation of pseudo-continuous arterial spin labelling (pCASL) MRI in the kidneys Andrew Malone, James F. Meaney, Andrew Fagan National Centre for Advanced Medical Imaging (CAMI), St James Hospital/TCD, Ireland This paper describes the optimisation of a new MRI technique for evaluating perfusion in the kidney without using an exogenous contrast agents. The kidneys play a pivotal role in the overall functioning of the body by removing waste products and maintaining blood pH and electrolyte balance. Perfusion provides an important biomarker of how well the kidneys are functioning. A pseudo-continuous arterial spin labelling (pCASL) protocol was set-up on a 3T scanner (Achieva, Philips) using a 32-channel detector coil. A single slice was selected positioned obliquely in kidney, with the label plane positioned perpendicularly in the aorta to avoid both the kidneys and the bottom of the heart. A sequence of consecutive breathholds were used to limit bulk kidney motion. 11 healthy volunteers were recruited onto the study after giving ethical consent. The following acquisition and image processing parameters were varied: spatial resolution, use of fat suppression, number of signal averages, and the effect of image registration to remove respiratory motion. The increased SNR of the lowered resolution provided a 36.1% increase in perfusion quantification precision. The use of fat suppression showed a 20.8% increase in SNR and a 31.4% increase in perfusion quantification precision. A minimum of 32–40 signal averages were found to maximise SNR. Finally, it was established that the most accurate perfusion values were obtained using a combination of linear and non-linear registration, yielding a 47.9% increase in perfusion quantification precision. This protocol holds significant promise for future clinical use. http://dx.doi.org/10.1016/j.ejmp.2016.05.011
Error quantification in pharmacokinetic parameters derived from DCE-MRI data using a novel anthropomorphic dynamic prostate phantom Silvin P. Knight a, Jacinta E. Browne b, James F. Meaney a, David S. Smith c, Andrew J. Fagan a a National Centre for Advanced Medical Imaging (CAMI), St James Hospital/TCD, Ireland b School of Physics & Medical Ultrasound Physics and Technology Group, Centre of Industrial Engineering Optics, FOCAS, DIT, Ireland c Institute of Imaging Science/Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, United States Pharmacokinetic (PK) modelling of dynamic contrast enhanced (DCE) MRI data has shown considerable promise in the detection of many cancers, including prostate. However, the clinical implementation of DCE-MRI acquisition protocols suitable for PK modelling has been greatly hindered by the lack of consistency with published PK parameter values, such as the volume-transfer
949
constant (Ktrans), with widely varying acquisition protocols and PK modelling approaches adding to the confusion. A novel anthropomorphic dynamic prostate phantom has been developed to address this shortcoming. The device is capable of simultaneously producing two distinct contrast time-intensity curves (CTCs), representative of those observed in DCE-MRI data from healthy and tumorous prostate tissue, in an environment which closely mimics the male pelvic region. CTCs were measured using a custom-built optical scanner, and ‘ground truth’ PK parameter values derived from the data. DCE-MRI data were acquired using a 3T scanner (Achieva, Philips, Netherlands) and a 16-channel phased array detector coil (3D-SPGR, TR/TE = 3.6/1.75 ms, flip = 10°, voxel size = 1.1 1.1 4 mm3, FOV = 224 224 72 mm3, slices = 18). The parallel imaging factor and number of signal averages were varied to give temporal resolutions from 2.3 s to 20.3 s. Ktrans values derived from MR data from the phantom were compared with the ground truth values and were found to differ by 8.1% to 44.6%, with the lowest variance from ground truth values achieved at a temporal resolution of 6.8 s. The phantom provides a model system on which the quantitative validation of new prostate DCE-MRI protocols can be performed, and could contribute to the standardisation of clinical prostate DCE-MRI acquisition protocols. http://dx.doi.org/10.1016/j.ejmp.2016.05.012
Effect of MR contrast agent on quantitative PET during simultaneous PET-MR imaging in cardiology Jim O’Doherty a, Paul Schleyer b a College London, UK b Siemens Healthcare, UK Background MR sequences used in the determination of PET linear attenuation coefficients (LAC) are a common procedure in simultaneous PET-MRI scanning. However during dynamic PET imaging, the introduction of gadolinium-based contrast agents (MRCA) at high concentrations during a dual injection of MRCA and PET radiotracer may cause attenuation effects of the PET radiotracer, and thus errors in quantification of dynamic images. Method We performed simultaneous PET-MR imaging of a phantom using increasing MRCA concentration from 0 to 65 mM (based on MRCA left ventricular concentration in a clinical study) mixed with water and 25 MBq of [18F]-FDG. LAC of the solution was calculated by a mixture rule and compared to measurements from CT images and automated MR LAC segmentation. The effect of increases in the resulting LAC over 0–65 mM was evaluated on a simulated image-derived arterial input function (IDIF) used in the PET kinetic model. Results From 0 to 46 mM, MR segmentation applied a LAC of 0.1 cm 1, and at >46 mM the LAC = 0.0854 cm 1 due to T1 shortening effects. Our results show an increase of only 1.3% in the LAC of the solution over the range of 0–65 mM of MRCA, with an effect on the area under an IDIF of <2%. Thus a minor error is propagated forward to the kinetic model. Conclusion The presence of high MRCA concentration in solution with PET radiotracer produces a minimal effect on PET quantification, provides <2% error to the calculation of perfusion parameters from kinetic models. http://dx.doi.org/10.1016/j.ejmp.2016.05.013
Radiotherapy Session Commissioning of the Intrabeam for Beaumont Hospital Donal Cummins, Pat McCavana St Luke’s Radiation Oncology Network (SLRON), Ireland