Limits...
Quantification of myocardial perfusion with self-gated cardiovascular magnetic resonance.

Likhite D, Adluru G, Hu N, McGann C, DiBella E - J Cardiovasc Magn Reson (2015)

Bottom Line: The gated and the self-gated datasets were then quantified with standard methods.Regional myocardial blood flow estimates (MBFs) obtained using self-gated systole (0.64 ± 0.26 ml/min/g), self-gated diastole (0.64 ± 0.26 ml/min/g), and ECG-gated scans (0.65 ± 0.28 ml/min/g) were similar.Based on the criteria for interchangeable methods listed in the statistical analysis section, the MBF values estimated from self-gated and gated methods were not significantly different.

View Article: PubMed Central - PubMed

ABSTRACT

Background: Current myocardial perfusion measurements make use of an ECG-gated pulse sequence to track the uptake and washout of a gadolinium-based contrast agent. The use of a gated acquisition is a problem in situations with a poor ECG signal. Recently, an ungated perfusion acquisition was proposed but it is not known how accurately quantitative perfusion estimates can be made from such datasets that are acquired without any triggering signal.

Methods: An undersampled saturation recovery radial turboFLASH pulse sequence was used in 7 subjects to acquire dynamic contrast-enhanced images during free-breathing. A single saturation pulse was followed by acquisition of 4-5 slices after a delay of ~40 msec. This was repeated without pause and without any type of gating. The same pulse sequence, with ECG-gating, was used to acquire gated data as a ground truth. An iterative spatio-temporal constrained reconstruction was used to reconstruct the undersampled images. After reconstruction, the ungated images were retrospectively binned ("self-gated") into two cardiac phases using a region of interest based technique and deformably registered into near-systole and near-diastole. The gated and the self-gated datasets were then quantified with standard methods.

Results: Regional myocardial blood flow estimates (MBFs) obtained using self-gated systole (0.64 ± 0.26 ml/min/g), self-gated diastole (0.64 ± 0.26 ml/min/g), and ECG-gated scans (0.65 ± 0.28 ml/min/g) were similar. Based on the criteria for interchangeable methods listed in the statistical analysis section, the MBF values estimated from self-gated and gated methods were not significantly different.

Conclusion: The self-gated technique for quantification of regional myocardial perfusion matched ECG-gated perfusion measurements well in normal subjects at rest. Self-gated systolic perfusion values matched ECG-gated perfusion values better than did diastolic values.

No MeSH data available.


Acquisition schematic for gated and ungated. a) Schematic of a gated acquisition. The scanner starts acquisition with the detection of the R wave. However, even before the 4th slice is acquired, another R wave is detected. This is possible if for example the heartrate increases. b) Schematic of an ungated acquisition. The scanner ignores the trigger signal and does a continuous acquisition.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC4325943&req=5

Fig1: Acquisition schematic for gated and ungated. a) Schematic of a gated acquisition. The scanner starts acquisition with the detection of the R wave. However, even before the 4th slice is acquired, another R wave is detected. This is possible if for example the heartrate increases. b) Schematic of an ungated acquisition. The scanner ignores the trigger signal and does a continuous acquisition.

Mentions: Various techniques, such as filtering the ECG signal or designing circuits to suppress noise pickup in ECG leads [2-4], have been proposed to obtain a good ECG-gating signal. Vector-cardiogram (VCG) based triggering, a popular method, helps to separate the electrocardiogram R-wave from the magnetohydrodynamic artifact [6]. However, even with these advances, ECG-gating is still problematic for some studies. This is evidenced in part by recent efforts towards self-gated approaches that do not require the ECG signal. The use of a separate self-gating readout [7], center of k space based gating [8] and center of mass based gating [9] have been presented recently for cine imaging at 1.5 T. Promising results for self-gated vascular imaging have been reported in [10]. Self-gated cardiac perfusion however is a bit different. Cardiac perfusion images are obtained with dynamic contrast enhanced (DCE) CMR in order to track the uptake and washout of a gadolinium-based contrast agent over time [11-14]. For cardiac perfusion DCE, T1-weighted images synchronized to the motion of the heart are obtained. The time series of images are assessed visually and/or analyzed using semi-quantitative or quantitative models to evaluate perfusion parameters. Cardiac perfusion DCE CMR acquisitions typically rely on the electrocardiogram (ECG) signal in order to fulfill the goal of synchronization. Unlike segmented acquisitions like cine imaging that acquire a portion of the k-space for each image in each heartbeat, DCE perfusion acquires all of the data each heartbeat to give a temporal resolution adequate for tracking the gadolinium contrast changes. This means that if all of the prescribed slices have not been imaged before the next R-wave trigger, then the scanner will miss acquiring during the next beat. This problem is exacerbated when slices are prescribed during rest for the stress portion of the perfusion exam. During stress imaging, the heart rate changes, so fewer slices may fit into the R-R interval. This can cause the scanner to acquire data only during alternate beats. Figure 1a shows an example where the scanner starts the acquisition process with the arrival of the first R wave. However even before the 4th slice is acquired, the second R wave arrives. Thus the second R-wave is ignored and no information is acquired during the second R-R interval. A critical missed beat, especially during uptake of contrast, can lead to erroneous quantification results.Figure 1


Quantification of myocardial perfusion with self-gated cardiovascular magnetic resonance.

Likhite D, Adluru G, Hu N, McGann C, DiBella E - J Cardiovasc Magn Reson (2015)

Acquisition schematic for gated and ungated. a) Schematic of a gated acquisition. The scanner starts acquisition with the detection of the R wave. However, even before the 4th slice is acquired, another R wave is detected. This is possible if for example the heartrate increases. b) Schematic of an ungated acquisition. The scanner ignores the trigger signal and does a continuous acquisition.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4325943&req=5

Fig1: Acquisition schematic for gated and ungated. a) Schematic of a gated acquisition. The scanner starts acquisition with the detection of the R wave. However, even before the 4th slice is acquired, another R wave is detected. This is possible if for example the heartrate increases. b) Schematic of an ungated acquisition. The scanner ignores the trigger signal and does a continuous acquisition.
Mentions: Various techniques, such as filtering the ECG signal or designing circuits to suppress noise pickup in ECG leads [2-4], have been proposed to obtain a good ECG-gating signal. Vector-cardiogram (VCG) based triggering, a popular method, helps to separate the electrocardiogram R-wave from the magnetohydrodynamic artifact [6]. However, even with these advances, ECG-gating is still problematic for some studies. This is evidenced in part by recent efforts towards self-gated approaches that do not require the ECG signal. The use of a separate self-gating readout [7], center of k space based gating [8] and center of mass based gating [9] have been presented recently for cine imaging at 1.5 T. Promising results for self-gated vascular imaging have been reported in [10]. Self-gated cardiac perfusion however is a bit different. Cardiac perfusion images are obtained with dynamic contrast enhanced (DCE) CMR in order to track the uptake and washout of a gadolinium-based contrast agent over time [11-14]. For cardiac perfusion DCE, T1-weighted images synchronized to the motion of the heart are obtained. The time series of images are assessed visually and/or analyzed using semi-quantitative or quantitative models to evaluate perfusion parameters. Cardiac perfusion DCE CMR acquisitions typically rely on the electrocardiogram (ECG) signal in order to fulfill the goal of synchronization. Unlike segmented acquisitions like cine imaging that acquire a portion of the k-space for each image in each heartbeat, DCE perfusion acquires all of the data each heartbeat to give a temporal resolution adequate for tracking the gadolinium contrast changes. This means that if all of the prescribed slices have not been imaged before the next R-wave trigger, then the scanner will miss acquiring during the next beat. This problem is exacerbated when slices are prescribed during rest for the stress portion of the perfusion exam. During stress imaging, the heart rate changes, so fewer slices may fit into the R-R interval. This can cause the scanner to acquire data only during alternate beats. Figure 1a shows an example where the scanner starts the acquisition process with the arrival of the first R wave. However even before the 4th slice is acquired, the second R wave arrives. Thus the second R-wave is ignored and no information is acquired during the second R-R interval. A critical missed beat, especially during uptake of contrast, can lead to erroneous quantification results.Figure 1

Bottom Line: The gated and the self-gated datasets were then quantified with standard methods.Regional myocardial blood flow estimates (MBFs) obtained using self-gated systole (0.64 ± 0.26 ml/min/g), self-gated diastole (0.64 ± 0.26 ml/min/g), and ECG-gated scans (0.65 ± 0.28 ml/min/g) were similar.Based on the criteria for interchangeable methods listed in the statistical analysis section, the MBF values estimated from self-gated and gated methods were not significantly different.

View Article: PubMed Central - PubMed

ABSTRACT

Background: Current myocardial perfusion measurements make use of an ECG-gated pulse sequence to track the uptake and washout of a gadolinium-based contrast agent. The use of a gated acquisition is a problem in situations with a poor ECG signal. Recently, an ungated perfusion acquisition was proposed but it is not known how accurately quantitative perfusion estimates can be made from such datasets that are acquired without any triggering signal.

Methods: An undersampled saturation recovery radial turboFLASH pulse sequence was used in 7 subjects to acquire dynamic contrast-enhanced images during free-breathing. A single saturation pulse was followed by acquisition of 4-5 slices after a delay of ~40 msec. This was repeated without pause and without any type of gating. The same pulse sequence, with ECG-gating, was used to acquire gated data as a ground truth. An iterative spatio-temporal constrained reconstruction was used to reconstruct the undersampled images. After reconstruction, the ungated images were retrospectively binned ("self-gated") into two cardiac phases using a region of interest based technique and deformably registered into near-systole and near-diastole. The gated and the self-gated datasets were then quantified with standard methods.

Results: Regional myocardial blood flow estimates (MBFs) obtained using self-gated systole (0.64 ± 0.26 ml/min/g), self-gated diastole (0.64 ± 0.26 ml/min/g), and ECG-gated scans (0.65 ± 0.28 ml/min/g) were similar. Based on the criteria for interchangeable methods listed in the statistical analysis section, the MBF values estimated from self-gated and gated methods were not significantly different.

Conclusion: The self-gated technique for quantification of regional myocardial perfusion matched ECG-gated perfusion measurements well in normal subjects at rest. Self-gated systolic perfusion values matched ECG-gated perfusion values better than did diastolic values.

No MeSH data available.