BLACK-BLOOD MR ANGIOGRAPHY

Exploration of anatomical distribution of brain metastasis from breast cancer at first diagnosis assisted by artificial intelligence

Objectives

This study aimed to explore the spatial distribution of brain metastases (BMs) from breast cancer (BC) and to identify the high-risk sub-structures in BMs that are involved at first diagnosis.

Methods

Magnetic resonance imaging (MRI) scans were retrospectively reviewed at our centre. The brain was divided into eight regions according to its anatomy and function, and the volume of each region was calculated. The identification and volume calculation of metastatic brain lesions were accomplished using an automatically segmented 3D BUC-Net model. The observed and expected rates of BMs were compared using 2-tailed proportional hypothesis testing.

Results

A total of 250 patients with BC who presented with 1694 BMs were retrospectively identified. The overall observed incidences of the substructures were as follows: cerebellum, 42.1 %; frontal lobe, 20.1 %; occipital lobe, 9.7 %; temporal lobe, 8.0 %; parietal lobe, 13.1 %; thalamus, 4.7 %; brainstem, 0.9 %; and hippocampus, 1.3 %. Compared with the expected rate based on the volume of different brain regions, the cerebellum, occipital lobe, and thalamus were identified as higher risk regions for BMs (P value ≤ 5.6*10-3). Sub-group analysis according to the type of BC indicated that patients with triple-negative BC had a high risk of involvement of the hippocampus and brainstem.

Conclusions

Among patients with BC, the cerebellum, occipital lobe and thalamus were identified as higher-risk regions than expected for BMs. The brainstem and hippocampus were high-risk areas of the BMs in triple negative breast cancer. However, further validation of this conclusion requires a larger sample size.

MR Angiography: Contrast-Enhanced Acquisition Techniques

Contrast-enhanced MR angiography (CE-MRA) is a frequently used MR imaging technique for evaluating cardiovascular structures. In many ways, it is similar to contrast-enhanced computed tomography (CT) angiography, except a gadolinium-based contrast agent (instead of iodinated contrast) is injected. Although the physiological principles of contrast injection overlap, the technical factors behind enhancement and image acquisition are different. CE-MRA provides an excellent alternative to CT for vascular evaluation and follow-up without requiring nephrotoxic contrast and ionizing radiation. This review describes the physical principles, limitations, and technical applications of CE-MRA techniques.

Tailoring encodable lanthanide-binding tags as MRI contrast agents

Lanthanide-binding tags (LBTs), peptide-based coexpression tags with high affinity for lanthanide ions, have previously been applied as luminescent probes to provide phasing for structure determination in X-ray crystallography and to provide restraints for structural refinement and distance information in NMR. The native affinity of LBTs for Gd(3+) indicates their potential as the basis for engineering of peptide-based MRI agents. However, the lanthanide coordination state that enhances luminescence and affords tightest binding would not be ideal for applications of LBTs as contrast agents, due to the exclusion of water from the inner coordination sphere. Herein, we use structurally defined LBTs as the starting point for re-engineering the first coordination shell of the lanthanide ion to provide for high contrast through direct coordination of water to Gd(3+) (resulting in the single LBT peptide, m-sLBT). The effectiveness of LBTs as MRI contrast agents was examined in vitro through measurement of binding affinity and proton relaxivity. For imaging applications that require targeted observation, fusion to specific protein partners is desirable. However, a fusion protein comprising a concatenated double LBT (dLBT) as an N-terminal tag for the model protein ubiquitin had reduced relaxivity compared with the free dLBT peptide. This limitation was overcome by the use of a construct based on the m-sLBT sequence (q-dLBT-ubiquitin). The structural basis for the enhanced contrast was examined by comparison of the X-ray crystal structure of xq-dLBT-ubiquitin (wherein two tryptophan residues are replaced with serine), to that of dLBT-ubiquitin. The structure shows that the backbone conformational dynamics of the MRI variant may allow enhanced water exchange. This engineered LBT represents a first step in expanding the current base of specificity-targeted agents available.

Color Doppler ultrasonography of the abdominal aorta

Alterations of the abdominal aorta are relatively common, particularly in older people. Technological advances in the fields of ultrasonography, computed tomography, angiography, and magnetic resonance imaging have greatly increased the imaging options for the assessment of these lesions. Because it can be done rapidly and is also non-invasive, ultrasonography plays a major role in the exploration of the abdominal aorta, from its emergence from the diaphragm to its bifurcation. It is indicated for the diagnosis and follow-up of various aortic diseases, especially aneurysms. It can be used to define the shape, size, and location of these lesions, the absence or presence of thrombi and their characteristics. It is also useful for monitoring the evolution of the lesion and for postoperative follow-up. However, its value is limited in surgical planning and in emergency situations.

Cardiovascular MRI: its current and future use in clinical practice

Cardiovascular magnetic resonance (CMR) imaging is a comprehensive clinical tool for assessing a large variety of cardiovascular diseases. Using the clinical service of the Duke Cardiovascular Magnetic Resonance Center as an example, we describe how to perform image contractile function, myocardial perfusion at stress and rest, myocardial viability, cardiovascular morphology, vascular anatomy and blood flow tests. The emergence of successful dedicated CMR services presents an opportunity to optimize patient throughput by streamlining the user interface of CMR scanners, standardizing the viewing format and reporting software, and customizing training programs to focus on the standardized CMR approaches. Accordingly, we discuss potential pathways to create these standards. Finally, we discuss several promising new CMR techniques we expect will complement existing clinical procedures.

From the RSNA Refresher Courses

Acquired diseases of the aorta and peripheral arteries are common. Owing to technical advances, magnetic resonance (MR) angiography has become the primary imaging modality for assessment of aortic and peripheral arterial disease. Contrast material-enhanced MR angiography is a rapid and robust technique that has emerged as the principal MR angiographic technique for evaluation of vascular disease. Two-dimensional time-of-flight MR angiography still has some well-validated applications, especially in distal peripheral vascular disease. Phase-contrast flow imaging is an important technique for quantification of blood flow. Black-blood imaging is a valuable tool for evaluation of the vessel wall. Understanding the principles of the main MR angiographic techniques is essential for consistent acquisition of diagnostic images. In addition, tailoring the acquisition parameters and the imaging protocol to the vessel being imaged and the clinical question is mandatory for optimal results. Future technical developments that will lead to faster image acquisition and better contrast agents promise to further improve image quality.

Characterization of complicated carotid plaque with magnetic resonance direct thrombus imaging in patients with cerebral ischemia

BACKGROUND

Thromboembolic disease secondary to complicated carotid atherosclerotic plaque is a major cause of cerebral ischemia. Clinical management relies on the detection of significant (>70%) carotid stenosis. A large proportion of patients suffer irreversible cerebral ischemia as a result of lesser degrees of stenosis. Diagnostic techniques that can identify nonstenotic high-risk plaque would therefore be beneficial. High-risk plaque is defined histologically if it contains hemorrhage/thrombus. Magnetic resonance direct thrombus imaging (MRDTI) is capable of detecting methemoglobin within intraplaque hemorrhage. We assessed this as a marker of complicated plaque and compared its accuracy with histological examination of surgical endarterectomy specimens.

METHODS AND RESULTS

Sixty-three patients underwent successful MRDTI and endarterectomy with histological examination. Of these, 44 were histologically defined as complicated (type VI plaque). MRDTI demonstrated 3 false-positive and 7 false-negative results, giving a sensitivity and specificity of 84%, negative predictive value of 70%, and positive predictive value of 93%. The interobserver (kappa=0.75) and intraobserver (kappa=0.9) agreement for reading MRDTI scans was good.

CONCLUSIONS

MRDTI of the carotid vessels in patients with cerebral ischemia is an accurate means of identifying histologically confirmed complicated plaque. The high contrast generated by short T1 species within the plaque allows for ease of interpretation, making this technique highly applicable in the research and clinical setting for the investigation of carotid atherosclerotic disease.

Quantification of vena cava blood flow with half Fourier echo-planar imaging

BACKGROUND

Human hemodynamics occurs in very short periods of time. To quantify blood flow under these circumstances, a fast-scan imaging technique is required. Echo-planar imaging can be a good candidate because it is able to acquire images in <50-100 msec. An imaging scheme with these properties can produce real-time images as well as overcome motion artifacts such as blurring and ghosting, which alter image quality. Additionally, echo-planar imaging does not require a calibration protocol to perform flow experiments in the human cardiovascular system. Consequently, echo-planar imaging appears to be the best imaging tool available to quantify blood flow in the vena cava. From a clinical point of view, echo-planar imaging has become a widespread commodity to produce magnetic resonance images in real-time.

METHODS

Flow-encoded half Fourier echo-planar imaging is proposed to determine blood flow in the arteries. This flow sequence was used to investigate vena cava blood flow in healthy volunteers and compared with other diagnostic imaging modalities.

RESULTS

Two-dimensional flow maps were obtained by using the two components (sine and cosine images) resulting from the flow-encoded echo-planar imaging sequence. Velocity profiles of vena cava of two healthy volunteers were calculated from the previous bidimensional blood flow maps.

CONCLUSIONS

We proved that real-time flow imaging of the cardiovascular system can be achieved with flow-encoded echo-planar imaging and a partial Fourier method. It is possible to quantify blood flow in the superior vena cava in humans. We believe that this imaging tool might offer relevant anatomic and physiologic information of the vena cava as well as of the cardiovascular system.