Toward quantitative fast diffusion kurtosis imaging with b-values chosen in consideration of signal-to-noise ratio and model fidelity.

PURPOSE: Diffusion kurtosis (DK) imaging is a variant of conventional diffusion magnetic resonance (MR) imaging that allows assessment of non-Gaussian diffusion. Fast DK imaging expedites the procedure by decreasing both scan time (acquiring the minimally required number of b-values) and computation time (obviating least-square curve fitting). This study aimed to investigate the applicability of fast DK imaging for both cerebral gray matter and white matter as a quantitative method. METHODS: Seventeen healthy volunteers were recruited and each provided written informed consent before participation. On a 3-Tesla clinical MR system, diffusion imaging was performed with 12 b-values ranging from 0 to 4000 s/mm2 . Diffusion encoding was along three orthogonal directions (slice selection, phase encoding, and frequency encoding) in separate series. Candidate b-values were chosen by first determining the maximum b-value (bmax ) in the context of signal-to-noise ratio and then assessing the model fidelity for all b-value combinations within bmax . Diffusion coefficient (D) and diffusion kurtosis coefficient (K) were derived from these candidates and assessed for their dependence on b-value combination. RESULTS: Our data suggested bmax to be 2200 s/mm2 as a trade-off between the percentage (~80%) of voxels statistically detectable against background and the sensitivity to non-Gaussian diffusion in both gray matter and white matter. The measurement dependence on b-value was observed predominantly in areas with a considerable amount of cerebrospinal fluid. In most gray matter and white matter, b-value combinations do not cause statistical difference in the calculated D and K. CONCLUSIONS: For fast DK imaging to be quantitatively applicable in both gray matter and white matter, bmax should be chosen to ensure adequate signal-to-noise ratio in the majority of gray/white matter and the two nonzero b-values should be chosen in consideration of model fidelity to mitigate the dependence of derived indices on b-values.

Positive Captopril Renography Without Renal Artery Stenosis but a Renal Cell Carcinoma.

A positive captopril renography indicates that patient's hypertension is renin dependent, most commonly caused by renal artery stenosis. The authors reported a case of positive captopril renography; however, CT demonstrated that renal arteries were intact, but there was a huge chromophobe renal cell carcinoma. Renin-dependent hypertension was relieved soon after nephrectomy. It is an uncommon cause of positive captopril renography.

Alterations of cerebral perfusion in asymptomatic internal carotid artery steno-occlusive disease.

Patients with asymptomatic occlusion in the internal carotid arteries (ICA) have been shown to have a better preserved hemodynamic status of the brain as compared to patients with symptoms. This study was aimed to explore the cerebral perfusion alterations in asymptomatic patients using multi-parametric arterial spin-labeling (ASL) magnetic resonance (MR) imaging. Forty-two patients diagnosed with asymptomatic ICA stenosis/occlusion were prospectively included and divided into high-grade (ultrasonographic stenosis ≥70%, N = 20) and low-grade groups (N = 22). On a 3-Tesla clinical MR scanner, pseudo-continuous ASL was performed to measure cerebral blood flow CBF, arterial transit time ATT, and flow territory. Fisher's exact test indicates that the high-grade group has higher frequency in asymmetric ATT (p < 10-3) and asymmetric flow territory (p < 10-3) as compared to the low-grade group. The between-group difference in CBF asymmetry is marginal (p = 0.062). Logistic regression further reveals that hemispherical asymmetry in ATT and flow territory is associated with the existence of high-grade ICA stenosis (odds ratio = 12 and 21, respectively), whereas hemispherical asymmetry in CBF is not. Our data suggest that ATT and flow territory may be better predictors of asymptomatic high-grade ICA stenosis diagnosed by carotid ultrasonography than CBF.

Aortic stiffness and interstitial myocardial fibrosis by native T1 are independently associated with left ventricular remodeling in patients with dilated cardiomyopathy.

Increased aortic stiffness is related to increased ventricular stiffness and remodeling. Myocardial fibrosis is the pathophysiological hallmark of failing heart. We investigated the relationship between noninvasive imaging markers of myocardial fibrosis, native T1, and late gadolinium enhancement, respectively, and aortic stiffness in ventricular remodeling. Consecutive patients with known dilated cardiomyopathy (n=173) underwent assessment of cardiac volumes and function, T1 mapping, scar imaging, and pulse wave velocity, a measure of aortic stiffness. Asymptomatic healthy volunteers served as controls (n=47). Controls and patients showed an increase in pulse wave velocity with age, which was accelerated in the presence of cardiovascular disease. On the contrary, native T1 increased with age in patients, but not in controls. Pulse wave velocity was associated with native T1 in the presence of disease, but not in health. Native T1 showed a strong relationship with markers of structural and functional left ventricular remodeling and diastolic impairment. Ischemic and nonischemic pathophysiology of ventricular remodeling showed a similar slope of relationship between pulse wave velocity and native T1. However, in nonischemic patients, increase in pulse wave velocity was associated with greater increase in native T1. Aortic stiffness is related to age, and this process is accelerated in the presence of disease. On the contrary, increase in interstitial myocardial fibrosis is associated with age in the presence of disease. Patients with ischemic and nonischemic dilated cardiomyopathy have a similar relationship between native T1 and pulse wave velocity, which is stronger in the latter group.

Contrast-enhanced cardiovascular magnetic resonance imaging of coronary vessel wall: state of art.

Coronary wall imaging by cardiovascular magnetic resonance (CMR) emerges as a promising method to detect vascular injury and remodeling directly within the coronary vascular wall. In this review, the current evidence on coronary wall enhancement using CMR is presented and summarized, with particular focus on its ability to detect inflammation in atherosclerosis, Takayasu's arteritis, acute coronary syndromes and immune-mediated inflammatory vasculitides. The authors review the possible mechanisms of coronary wall contrast enhancement on CMR and discuss the technical considerations and limitations. Lastly, the potential clinical applications and possibilities for future research are proposed.

Frequency and risk factors associated with atherosclerotic plaques in patients with a zero coronary artery calcium score.

BACKGROUND: Analysis of the coronary artery calcium levels usually provides important information that can be used in patient prognosis and stratification of treatment when coronary artery disease is suspected. However, plaques, with or without significant stenosis, have been reported in patients without coronary artery calcium. The aim of this study was to determine the frequency and risk factors of the development of coronary artery plaques in individuals with a zero calcium score. METHODS: Analysis of coronary artery calcium levels and coronary computed tomography angiography (CTA) were performed using 64-slice computed tomography (CT). The demographic data, clinical risk factors, and imaging features of 519 consecutive patients (54 ± 10 years, male:female ratio of 56:44) were retrospectively analyzed. The presence of plaques and the degree of the resulting stenosis were recorded. Descriptive, univariate, and multivariate analyses were carried out to identify the frequency and risk factors associated with the presence of coronary artery plaques. RESULTS: Among 66 patients, 82 coronary arteries were found to have plaques, and six coronary arteries showed significant stenosis. Univariate analysis showed that an age greater than 55 years, male gender, a body mass index (BMI) of more than 27, hypertension, and diabetes mellitus are significant factors associated with the development of coronary artery plaques. Multivariate logistic regression analysis showed that an age over 55 years (p = 0.012, OR = 2.13, 95% C.I. = 1.18-3.84) and BMI greater than 27 (p = 0.026, OR = 2.01, 95% C.I. = 1.09-3.72) are independent factors associated with the presence of plaques in patients with a zero calcium score. CONCLUSION: The results of this study show that plaques are present in a significant proportion of individuals with a zero coronary artery calcium score. In addition, advanced age and obesity are risk factors associated with the development of plaques.

Myocardial bridging in Taiwanese: noninvasive assessment by 64-detector row coronary computed tomographic angiography.

BACKGROUND: Myocardial bridging (MB) is a congenital structural variant in which a segment of the epicardial coronary artery tunnels into and is surrounded by the myocardium. MB has been correlated to some clinical complications of cardiovascular disease (CVD). The depiction rate of MB varies significantly between catheter coronary angiography and autopsy studies. This study aimed to assess the depiction rate of MB among Taiwanese by coronary computed tomographyic angiography (CCTA), to determine the anatomical features of the tunneling vessels, and to evaluate the outcome of patients having MB. METHODS: Between September 2006 and December 2007, 425 subjects (264 men and 161 women; mean age 59.6 ± 11.7 years) underwent ECG-gated CCTA by a 64-dectector row scanner in our institution. The presence and the location of MB in CCTA images and the presence of atherosclerosis in the tunneling vessels were evaluated and recorded. Major CVD events in the cohort were tracked from the day of CCTA examination until on March 2009 termination of follow-up. RESULTS: The depiction rate of MB was 20.9% (89/425). A total of 122 MB were depicted by CCTA. Thirty-six tunneling segments (29.5%) were situated in the distal portion of the left anterior descending coronary artery (LAD), 23 segments (18.8%) were in the middle portion of the LAD, 19 (15.5%) were in the first obtuse marginal branch of the left circumflex artery, 18 (14.7%) in the first diagonal branch of the LAD, and 10 (8.1%) were in the ramus medianus. Nine tunneling segments (7.3%) had concomitant atherosclerotic plaques at the time of CCTA. One hundred and nine tunneled segments (89.3%) were superficially located in the myocardium, with a mean depth of 1.9 ± 0.81 mm (range, 0.9-4 mm). Twelve patients with CVD events were recorded during the mean follow-up interval of 21.91 ± 4.03 months (range, 3.08-28.82 months). All 12 patients with CVD events had no MB on CCTA. CONCLUSION: The depiction rate of MB by CCTA was 20.9% in this study. The most common location of MB was in the LAD. Concomitant atherosclerotic plaques were found in 7.3% of MB cases. Eighty-nine percent of tunneling vessels were superficially situated. None of the enrolled subjects with MB developed CVD event during the follow-up period. No statistical correlation was found between the presence of MB and CVD event (p = 0.057).