Myocardial First Pass Perfusion Imaging With Gadobutrol

Cardiovascular Imaging: The Past and the Future, Perspectives in Computed Tomography and Magnetic Resonance Imaging

Today's noninvasive imaging of the cardiovascular system has revolutionized the approach to various diseases and has substantially affected prognostic information. Cardiovascular magnetic resonance (MR) and computed tomographic (CT) imaging are at center stage of these approaches, although 5 decades ago, these technologies were unheard of. Both modalities had their inception in the 1970s with a primary focus on noncardiovascular applications. The technical development of the various decades, however, substantially pushed the envelope for cardiovascular MR and CT applications. Within the past 10-15 years, MR and CT technologies have pushed each other in cardiac applications; and without the "rival" modality, neither one would likely not have reached its potential today. This view on the history of MR and CT in the field of cardiovascular applications provides insight into the story of success of applications that once have been ideas only but are at prime time today.

[Cardiac magnetic resonance imaging: from imaging to diagnosis]

Cardiac magnetic resonance imaging (CMR) has evolved over the past 20 years from a research-based imaging modality to an indispensable routine procedure in cardiac diagnostics. In addition to the morphological representation of cardiac anatomy, whereby only noninvasive multidetector computed tomography (MDCT) is superior, another strength of CMR is the assessment of cardiac function and tissue differentiation. This requires that the radiologist performing the examination and analyzing the results has good knowledge of cardiac and thoracic anatomy and a detailed knowledge of the various cardiovascular diseases, hemodynamics, and pathophysiology. CMR reliably allows determination of a range of easy to determine quantitative parameters such as ventricular ejection fraction and also the valvular regurgitation fraction, which allows objective assessment of cardiac function. Especially the possibility to differentiate inflamed, viable, and ischemic tissue using adenosine stress MRI in the last 10 years has led to routine use of CMR. Even compared to competing nuclear medicine procedures, CMR is important for treatment decision-making and for prognosis estimation, thus, making it an indispensable component of cardiovascular diagnostics.

Myocardial perfusion MRI with an undersampled 3D stack-of-stars sequence

PURPOSE

To determine the feasibility of three-dimensional (3D) hybrid radial (stack-of-stars) MRI with spatiotemporal total variation (TV) constrained reconstruction for dynamic contrast enhanced myocardial perfusion imaging.

METHODS

An ECG-triggered saturation recovery turboFLASH sequence with undersampled stack-of-stars sampling with spatiotemporal TV constrained reconstruction was developed for dynamic contrast enhanced myocardial perfusion imaging. Simulations were performed to study the dependence of the approach to steady state on flip angle and saturation recovery time for this stack-of-stars acquisition. Phantom studies were used to show the effect of the flip angle selection and imperfect spoiling on image qualities. Studies were done in three humans to test the feasibility of the approach for myocardial perfusion imaging.

RESULTS

The simulation and phantom studies showed that imperfect spoiling and magnetization changes during the readout were a function of flip angle and nonoptimized selection of flip angle could degrade the images. Low flip angle acquisitions in the human subjects result in images with good quality similar to multislice radial 2D images.

CONCLUSIONS

3D stack-of-stars sampling with spatiotemporal TV constrained reconstruction provides a promising alternative for myocardial perfusion imaging.

Magnetic resonance perfusion of the myocardium: semiquantitative and quantitative evaluation in comparison with coronary angiography and fractional flow reserve

PURPOSE

The aim of this study was to investigate if a quantitative evaluation of a magnetic resonance (MR) perfusion examination of the myocardium can achieve a comparable diagnostic accuracy as a semiquantitative evaluation.

METHODS

A total of 31 patients with suspected coronary artery disease underwent MR imaging and conventional coronary angiography. Stenoses with a diameter reduction between 50% and 75% were evaluated by an intracoronary pressure wire examination (fractional flow reserve) for assessment of their hemodynamic relevance. A 0.05 mmol/kg contrast material bolus (gadopentetate dimeglumine) was applied during adenosine-induced stress (140 μg/kg/min) and at rest with a flow rate of 5 mL/s. Signal intensity time curves of the first-pass MR perfusion images, acquired at rest and under adenosine stress with a Saturation Recovery-turbo Fast Low Angle Shot Magnetic Resonance Imaging sequence, were analyzed by Argus Dynamic Signal Analysis (Siemens Healthcare, Erlangen, Germany). For the semiquantitative evaluation, the upslope value of a linear fit from the foot point to the signal maximum was calculated for 18 segments (signal intensity units per second). For the quantitative evaluation, a model-independent deconvolution was used to calculate coronary blood flow (MBF in mL/100 g/min). For each segment for the stress and rest examination, upslope value and MBF were determined. In addition, the ratio of the stress and rest value for each segment was determined (myocardial perfusion reserve index [MPRI]). The mean value of the 2 segments with the lowest value was calculated for each patient. Coronary artery stenosis greater than 75% or greater than 50% with positive fractional flow reserve less than 0.75 was considered as hemodynamically relevant. Receiver-operator-curves were calculated.

RESULTS

The values of the area under the ROC curves were 0.74, 0.66, and 0.92 for the US(Stress), US(Rest), and US(MPRI) evaluations (semiquantitative evaluation). The values for the MBF(Stress), MBF(Rest), and MBF(MPRI) evaluations (quantitative evaluation) were 0.92, 0.68, and 0.84, respectively. Comparing US(MPRI) and MBF(Stress), identical values and no significant difference were found for the area under the ROC curves.

CONCLUSION

A quantitative evaluation using a model-free deconvolution provides identical diagnostic performance when only a stress examination is used, much similar to a semiquantitative evaluation, if both stress and rest examinations are used.

Intraindividual comparison of gadobutrol and gadopentetate dimeglumine for detection of myocardial late enhancement in cardiac MRI

OBJECTIVE

Gadobutrol is an extracellular macrocyclic gadolinium chelate recently introduced in MRI, and it has already been used for cardiac late enhancement imaging; however, until now it has never been compared with gadopentetate dimeglumine. The purpose of our study was to compare 0.1 mmol/kg gadobutrol to 0.2 mmol/kg gadopentetate dimeglumine for the detection of myocardial late enhancement in the same group of patients.

SUBJECTS AND METHODS

This was an exploratory single-blind parallel group study comparing gadobutrol (0.1 mmol/kg) to gadopentetate dimeglumine (0.2 mmol/kg) in 20 adult patients scheduled for cardiac late enhancement MRI with gadopentetate dimeglumine and whose MR images showed late enhancement. MR images were acquired at 10, 15, and 20 minutes after peripheral injection of gadobutrol by using a 3D turbo field echo inversion recovery T1-weighted sequence. Volume and percentage of late enhancement, number of involved segments, late enhancement localization and pattern, and late enhancement signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were compared between contrast agents.

RESULTS

Late enhancement was not significantly different with gadobutrol and gadopentetate dimeglumine both in terms of total volume of myocardium (mean ± SD, 37.8 ± 56.1 and 35.1 ± 46.7 cm(3), respectively; p = 0.33) and percentage of myocardial wall involvement (22.5% ± 19.1% and 22.0% ± 17.2%, respectively; p = 0.67). The number of segments involved was not different (138 with gadobutrol vs 134 with gadopentetate dimeglumine). Furthermore, SNR and CNR were not different (gadopentetate dimeglumine, 123.8 ± 82.9 and gadobutrol, 117.2 ± 88.6, p = 0.58 and gadopentetate dimeglumine, 96.2 ± 68.9 and gadobutrol, 88.4 ± 72.9, p = 0.53, respectively).

CONCLUSION

A single dose of gadobutrol seems to be as effective as a double dose of gadopentetate dimeglumine for the detection of late enhancement.

MRI and CT in the diagnosis of coronary artery disease: indications and applications

In recent years, technical advances and improvements in cardiac computed tomography (CT) and cardiac magnetic resonance imaging (MRI) have provoked increasing interest in the potential clinical role of these techniques in the non-invasive work-up of patients with suspected coronary artery disease (CAD) and correct patient selection for these emerging imaging techniques. In the primary detection or exclusion of significant CAD, e.g. in the patient with unspecific thoracic complaints, and also in patients with known CAD or advanced stages of CAD, both CT and MRI yield specific advantages. In this review, the major aspects of non-invasive MR and CT imaging in the diagnosis of CAD will be discussed. The first part describes the clinical value of contrast-enhanced non-invasive CT coronary angiography (CTCA), including the diagnostic accuracy of CTCA for the exclusion or detection of significant CAD with coronary artery stenoses that may require angioplastic intervention, as well as potentially valuable information on the coronary artery vessel wall. In the second section, the potential of CT for the imaging of myocardial viability and perfusion will be highlighted. In the third and final part, the range of applications of cardiac MRI in CAD patients will be outlined.

Myocardial perfusion magnetic resonance imaging using sliding-window conjugate-gradient HYPR methods in canine with stenotic coronary arteries

PURPOSE

First-pass perfusion magnetic resonance imaging (MRI) is a promising technique for detecting ischemic heart disease. However, the diagnostic value of the method is limited by the low spatial coverage, resolution, signal-to-noise ratio (SNR), and cardiac motion-related image artifacts. A combination of sliding window and conjugate-gradient HighlY constrained back-PRojection reconstruction (SW-CG-HYPR) method has been proposed in healthy volunteer studies to reduce the acquisition window for each slice while maintaining the temporal resolution of 1 frame per heartbeat in myocardial perfusion MRI. This method allows for improved spatial coverage, resolution, and SNR.

METHODS

In this study, we use a controlled animal model to test whether the myocardial territory supplied by a stenotic coronary artery can be detected accurately by SW-CG-HYPR perfusion method under pharmacological stress.

RESULTS

Results from 6 mongrel dogs (15-25 kg) studies demonstrate the feasibility of SW-CG-HYPR to detect regional perfusion defects. Using this method, the acquisition time per cardiac cycle was reduced by a factor of 4, and the spatial coverage was increased from 2 to 3 slices to 6 slices as compared with the conventional techniques including both turbo-Fast Low Angle Short (FLASH) and echoplanar imaging (EPI). The SNR of the healthy myocardium at peak enhancement with SW-CG-HYPR (12.68 ± 2.46) is significantly higher (P < 0.01) than the turbo-FLASH (8.65 ± 1.93) and EPI (5.48 ± 1.24). The spatial resolution of SW-CG-HYPR images is 1.2 × 1.2 × 8.0 mm, which is better than the turbo-FLASH (1.8 × 1.8 × 8.0 mm) and EPI (2.0 × 1.8 × 8.0 mm).

CONCLUSIONS

Sliding-window CG-HYPR is a promising technique for myocardial perfusion MRI. This technique provides higher image quality with respect to significantly improved SNR and spatial resolution of the myocardial perfusion images, which might improve myocardial perfusion imaging in a clinical setting.

Advances in magnetic resonance (2008)

Current advances in magnetic resonance, as a diagnostic modality, are discussed in the context of publications from Investigative Radiology during 2007 and 2008. The articles relating to this topic, published during the past 2 years, are reviewed by anatomic region. The discussion concludes with a consideration of magnetic resonance contrast media, focusing on studies published in the journal, and examining in particular the potential impact of nephrogenic systemic fibrosis.