The capability of detecting small vessels beyond the conventional MRI sensitivity using iron‐based contrast agent enhanced susceptibility weighted imaging

Imaging brain microvasculature is important in cerebrovascular diseases. However, there is still a lack of non‐invasive, non‐radiation, and whole‐body imaging techniques to investigate them. The aim of this study is to develop an ultra‐small superparamagnetic iron oxide (USPIO) enhanced susceptibility weighted imaging (SWI) method for imaging micro‐vasculature in both animal (~10 μm in rat) and human brain. We hypothesized that the USPIO‐SWI technique could improve the detection sensitivity of the diameter of small subpixel vessels 10‐fold compared with conventional MRI methods. Computer simulations were first performed with a double‐cylinder digital model to investigate the theoretical basis for this hypothesis. The theoretical results were verified using in vitro phantom studies and in vivo rat MRI studies (n = 6) with corresponding ex vivo histological examinations. Additionally, in vivo human studies (n = 3) were carried out to demonstrate the translational power of the USPIO‐SWI method. By directly comparing the small vessel diameters of an in vivo rat using USPIO‐SWI with the small vessel diameters of the corresponding histological slide using laser scanning confocal microscopy, 13.3‐fold and 19.9‐fold increases in SWI apparent diameter were obtained with 5.6 mg Fe/kg and 16.8 mg Fe/kg ferumoxytol, respectively. The USPIO‐SWI method exhibited its excellent ability to detect small vessels down to about 10 μm diameter in rat brain. The in vivo human study unveiled hidden arterioles and venules and demonstrated its potential in clinical practice. Theoretical modeling simulations and in vitro phantom studies also confirmed a more than 10‐fold increase in the USPIO‐SWI apparent diameter compared with the actual small vessel diameter size. It is feasible to use SWI blooming effects induced by USPIO to detect small vessels (down to 10 μm in diameter for rat brain), well beyond the spatial resolution limit of conventional MRI methods. The USPIO‐SWI method demonstrates higher potential in cerebrovascular disease investigations.     

Clinical effectiveness and radial artery remodeling assessment via very-high-frequency ultrasound/ultra biomicroscopy after applying slender 7Fr sheath for transradial approach in left main bifurcation disease

Abstract

Objective

To explore the clinical effect and radial remodeling of transradial slender 7?Fr sheath for left main bifurcation disease (LM bifurcation).     

In vivo characterization of emerging white matter microstructure in the fetal brain in the third trimester

The third trimester of pregnancy is a period of rapid development of fiber bundles in the fetal white matter. Using a recently developed motion‐tracked slice‐to‐volume registration (MT‐SVR) method, we aimed to quantify tract‐specific developmental changes in apparent diffusion coefficient (ADC), fractional anisotropy (FA), and volume in third trimester healthy fetuses. To this end, we reconstructed diffusion tensor images from motion corrected fetal diffusion magnetic resonance imaging data. With an approved protocol, fetal MRI exams were performed on healthy pregnant women at 3 Tesla and included multiple (2–8) diffusion scans of the fetal head (1–2 b = 0 s/mm² images and 12 diffusion‐sensitized images at b = 500 s/mm²). Diffusion data from 32 fetuses (13 females) with median gestational age (GA) of 33 weeks 4 days were processed with MT‐SVR and deterministic tractography seeded by regions of interest corresponding to 12 major fiber tracts. Multivariable regression analysis was used to evaluate the association of GA with volume, FA, and ADC for each tract. For all tracts, the volume and FA increased, and the ADC decreased with GA. Associations reached statistical significance for: FA and ADC of the forceps major; volume and ADC for the forceps minor; FA, ADC, and volume for the cingulum; ADC, FA, and volume for the uncinate fasciculi; ADC of the inferior fronto‐occipital fasciculi, ADC of the inferior longitudinal fasciculi; and FA and ADC for the corticospinal tracts. These quantitative results demonstrate the complex pattern and rates of tract‐specific, GA‐related microstructural changes of the developing white matter in human fetal brain.     

Morphology of ejaculatory ducts: A systematic review

The morphology of human ejaculatory ducts has not been well established. The objective of this study was to describe macroscopic and microscopic anatomy of ejaculatory ducts. We conducted a systematic review using MEDLINE, Scopus, PubMed, and Cochrane databases. Search terms were: “ejaculatory ducts,” “seminal colliculus,” “prostatic utricle,” “anatomy,” “histology,” “radiology,” and “embryology.” We only included studies assessing adult (>18 years) humans published before November 1, 2019. We excluded studies describing pathological ducts and case reports. Independent authors extracted data using predefined criteria. Fourteen studies were included in the qualitative synthesis. Usually, the ejaculatory ducts entered the prostate by piercing the central part of its base. Most studies identified an anteromedial curve of the ducts at the outset within the prostate, their subsequent course being a straight path towards the seminal colliculus, their terminal parts diverging immediately before joining the prostatic urethra. However, the morphology of the terminal part of the ducts was inconsistent. The mean length of the ducts ranged from 1.4 to 2.2 cm. In conclusion, the luminal diameter gradually decreased as the ducts traveled towards the seminal colliculus. Ejaculatory ducts angulate anteromedially at their onset within the prostate and travel straight towards the seminal colliculus. Their terminal parts diverge immediately before joining the prostatic urethra. However, the reported dimensions of the ducts differ among studies.     

Inherently decoupled 1H antennas and 31P loops for metabolic imaging of liver metastasis at 7 T

High field ³¹P spectroscopy has thus far been limited to diffuse liver disease. Unlike lower field‐strength scanners, there is no body coil in the bore of the 7 T and despite inadequate penetration depth (<10 cm), surface coils are the current state‐of‐the‐art for acquiring anatomical images to support multinuclear studies. We present a system of proton antennas and phosphorus loops for ³¹P spectroscopy and provide the first ultrahigh‐field phosphorus metabolic imaging of a tumor in the abdomen. Herein we characterize the degree to which antennas are isolated from underlying loops. Next, we evaluate the penetration depth of the two antennas available during multinuclear examinations. Finally, we combine phosphorus spectroscopy (two loops) with parallel transmit imaging (eight antennas) in a patient. The loops and antennas are inherently decoupled (no added circuitry, <0.1% power coupling). The penetration depth of two antennas gives twice that of conventional loops. The liver and full axial slice of the abdomen were imaged with eight transmit/receive antennas using parallel transmit B1‐shimming to overcome image voids. Phosphorus spectroscopy from a liver metastasis resolved individual peaks for phosphocholine and phosphoethenalomine. Proton antennas are inherently decoupled from phosphorus loops. By using two proton antennas it is possible to perform region‐of‐interest image‐based shimming in over 80% of the liver volume, thereby enabling phosphorus spectroscopy of localized disease. Shimming of the full extent of the abdominal cross‐section is feasible using a parallel transmit array of eight antennas. A system architecture capable of supporting eight‐channel parallel transmit and multinuclear spectroscopy is optimal for supporting multiparametric body imaging, including metabolic imaging, for monitoring the response of patients with liver metastases to cancer treatments and for patient risk stratification. In the meantime, the existing infrastructure using two antennas is sufficient for preliminary studies in metabolic imaging of tumors in the liver.     

Changes in white matter microstructure related to non-linguistic cognitive impairment in post-stroke aphasia

ABSTRACT

Objects

Post-stroke aphasia (PSA) often have non-linguistic cognitive impairment. We aimed to ascertain its characteristics of non-linguistic cognitive impairment and the corresponding changes in white matter microstructures.