Cardiovascular MR imaging: technique optimization and detection of disease in clinical practice

Building blocks for thoracic MRI: Challenges, sequences, and protocol design

Thoracic MRI presents important and unique challenges. Decreased proton density in the lung in combination with respiratory and cardiac motion can degrade image quality and render poorly executed sequences uninterpretable. Despite these challenges, thoracic MRI has an important clinical role, both as a problem-solving tool and in an increasing array of clinical indications. Advances in scanner and sequence design have also helped to drive this development, presenting the radiologist with improved techniques for thoracic MRI. Given this evolving landscape, radiologists must be familiar with what thoracic MR has to offer. The first step in developing an effective thoracic MRI practice requires the creation of efficient and malleable protocols that can answer clinical questions. To do this, radiologists must have a working knowledge of the MR sequences that are used in the thorax, many of which have been adapted from use elsewhere in the body. These sequences can be broadly divided into three categories: traditional/anatomic, functional, and cine based. Traditional/anatomic sequences allow for the depiction of anatomy and pathologic processes with the ability for characterization of signal intensity and contrast enhancement. Functional sequences, including diffusion-weighted imaging, and high temporal resolution dynamic contrast enhancement, allow for the noninvasive measurement of tissue-specific parameters. Cine-based sequences can depict the motion of structures in the thorax, either with retrospective ECG gating or in real time. The purpose of this article is to review these categories, the building block sequences that comprise them, and identify basic questions that should be considered in thoracic MRI protocol design. Level of Evidence: 5 Technical Efficacy Stage: 3 J. Magn. Reson. Imaging 2019;50:682-701.

Pain-related autonomic response is modulated by the medial prefrontal cortex: An ECG-fMRI study in men

BACKGROUND

Our goal was to identify brain structures responsible for pain-related autonomic changes by the correlation of simultaneously acquired functional magnetic resonance imaging (fMRI) and electrocardiogram (ECG) data.

METHODS

Eighteen healthy men (age: 22.89 ± 1.96) were involved. Painful sensation was evoked by heat. Simultaneously recorded brain fMRI and ECG data during pain were compared to data acquired during a non-painful heat sensation. From the ECG data, time- and frequency domain parameters of heart rate variability (HRV) were extracted.

RESULTS

We found that: (1) among the common elements of both pain network and central autonomic network (CAN) only the medial prefrontal frontal cortex (MPFC) showed significant correlation with HRV; (2) the parasympathetic response to the painful stimuli showed a positive, while the sympathetic response a negative association with pain related BOLD-signal change observed in MPFC; (3) time domain parameters of HRV were negatively associated with MPFC activation.

CONCLUSIONS

The novelty of our study-compared to previous ECG-fMRI studies-is that we used pain as stimulus and investigated both frequency- and time-domain parameters of HRV. Compared to other stimuli used in earlier studies to activate the CAN, pain sensation can be standardized easier and might allow us to better understand the functional organization of CAN. The results of the current ECG-fMRI study may have direct clinical relevance in understanding the pathomechanisms of several clinical conditions.

PERSPECTIVE

There are some simultaneous ECG-fMRI and ECG-Positron Emission Tomography (PET) studies, but limited information is available about the pain-related brain function-HRV relations. The novelty of our study is that we used pain as stimulus to activate the central autonomic network and investigated both frequency- and time-domain parameters of HRV.

In Vivo Serial Assessment of Aortic Aneurysm Formation in Apolipoprotein E–Deficient Mice via MRI

Background— Hyperlipidimic mice administered angiotensin II have been used for the study of abdominal aortic aneurysms (AAAs). The purpose of this study was to examine the use of MRI for studying AAA development and for examining the effects of pharmacological intervention on AAA development in the apolipoprotein E–deficient mouse.

Methods and Results— Suprarenal aortic aneurysms were generated in apolipoprotein E–deficient mice administered angiotensin II (1000 ng/kg per min) for up to 28 days. In vivo MRI was performed serially (once weekly) to assess AAA development and rupture. Comparison of AAA size as measured by in vivo and ex vivo MRI resulted in excellent agreement ( r =0.96, P <0.0001). In addition, MRI correlated with histology-derived AAA area assessment (in vivo versus histology: r =0.84, P <0.0001; ex vivo versus histology: r =0.89, P <0.0001). In a separate study, angiotensin II–administered apolipoprotein E–deficient mice were treated with doxycycline (broad-based matrix metalloproteinase inhibitor; 30 mg/kg per day for 28 days). MRI was able to noninvasively assess a reduced rate of AAA development (46% versus 71%, P <0.05), a decreased AAA area (2.56 versus 4.02 mm 2 , P <0.01), and decreased incidence of rupture (43% versus 100%) in treated versus control animals. Inhibition of aorta matrix metalloproteinase 2/9 activity was observed in the treated animals.

Conclusions— These results demonstrate the use of MRI to noninvasively and temporally assess AAA development on pharmacological intervention in this preclinical cardiovascular disease model.