Hemodynamic provocation with acetazolamide shows impaired cerebrovascular reserve in adults with sickle cell disease.

Sickle cell disease is characterized by chronic hemolytic anemia and vascular inflammation, which can diminish the vasodilatory capacity of the small resistance arteries, making them less adept at regulating cerebral blood flow. Autoregulation maintains adequate oxygen delivery, but when vasodilation is maximized, the low arterial oxygen content can lead to ischemia and silent cerebral infarcts. We used magnetic resonance imaging of cerebral blood flow to quantify whole-brain cerebrovascular reserve in 36 adult patients with sickle cell disease (mean age, 31.9±11.3 years) and 11 healthy controls (mean age, 37.4±15.4 years), and we used high-resolution 3D FLAIR magnetic resonance imaging to determine the prevalence of silent cerebral infarcts. Cerebrovascular reserve was calculated as the percentage change in cerebral blood flow after a hemodynamic challenge with acetazolamide. Co-registered lesion maps were used to demonstrate prevalent locations for silent cerebral infarcts. Cerebral blood flow was elevated in patients with sickle cell disease compared to controls (median [interquartile range]: 82.8 [20.1] vs 51.3 [4.8] mL/100g/min, P<0.001). Cerebral blood flow was inversely associated with age, hemoglobin, and fetal hemoglobin, and correlated positively with bilirubin, and LDH, indicating that cerebral blood flow may reflect surrogates of hemolytic rate. Cerebrovascular reserve in sickle cell disease was decreased by half compared to controls (34.1 [33.4] vs 69.5 [32.4] %, P<0.001) and was associated with hemoglobin and erythrocyte count indicating anemia-induced hemodynamic adaptations. In total, 29/36 patients (81%) and 5/11 controls (45%) had silent cerebral infarcts (median volume of 0.34 vs 0.02 mL, P=0.03). Lesions were preferentially located in the borderzone. In conclusion, patients with sickle cell disease have a globally reduced cerebrovascular reserve as determined by arterial spin labeling with acetazolamide and reflects anemia-induced impaired vascular function in sickle cell disease. This study was registered at clinicaltrials.gov identifier 02824406.

A computed tomography-based planning tool for predicting difficulty of minimally invasive aortic valve replacement.

OBJECTIVES: Minimally invasive aortic valve replacement has proven its value over the last decade by its significant advancement and reduction in mortality, morbidity and admission time. However, minimally invasive aortic valve replacement is associated with some on-site difficulties such as limited aortic annulus exposure. Currently, computed tomography scans are used to evaluate the anatomical relationship among the intercostal spaces, ascending aorta and aortic valve prior to surgery. We hypothesized that quantitative measurements of access distance and access angle are associated with outcome and access difficulty. METHODS: We introduce a novel minimally invasive aortic valve replacement planning prototype that allows automatic measurements of access angle, access distance and aortic annulus dimensions. The prototype visualizes these measurements on the chest cage as ISO contours. The association of these measures with outcome parameters such as extracorporeal circulation time, aortic cross-clamping time and access difficulty score was assessed. We included 14 patients who received a new valve by ministernotomy. RESULTS: The mean access angle was 40.3 ± 5.1°. It was strongly associated with aortic cross-clamping time (Pearson correlation coefficient = 0.60, P = 0.02) and access difficulty score (Spearman's rank correlation coefficient = 0.57, P = 0.03). Access angles were significantly different between easy and difficult access groups (P = 0.03). There was no significant association between access distance and outcome parameters. CONCLUSIONS: Access angle is strongly associated with procedure complexity. The automated presentation of this measure suggests added value of the prototype in clinical practice.

Dynamics of the aortic annulus in 4D CT angiography for transcatheter aortic valve implantation patients.

BACKGROUND: Transcatheter aortic valve implantation (TAVI) is a well-established treatment for patients with severe aortic valve stenosis. This procedure requires pre-operative planning by assessment of aortic dimensions on CT Angiography (CTA). It is well-known that the aortic root dimensions vary over the heart cycle. However, sizing is commonly performed at either mid-systole or end-diastole only, which has resulted in an inadequate understanding of its full dynamic behavior. STUDY GOAL: We studied the variation in annulus measurements during the cardiac cycle and determined if this variation is dependent on the amount of calcification at the annulus. METHODS: We measured and compared aortic root annular dimensions and calcium volume in CTA acquisitions at 10 cardiac cycle phases in 51 aortic stenosis patients. Sub-group analysis was performed based on the volume of calcium by splitting the population into mildly and severely calcified valves subgroups. RESULTS: For most annulus measurements, the largest differences were found between 10% and 70 to 80% cardiac cycle phases. Mean difference (±standard deviation) in annular minimum diameter, maximum diameter, area, and aspect ratio between mid-systole and end-diastole phases were 1.0 ± 0.29 mm (p = 0.065), 0.30 ± 0.24 mm (p = 0.7), 24.1 ± 7.6 mm2 (p < 0.001), and 0.041 ± 0.012 (p = 0.039) respectively. Calcium volume measurements varied strongly during the cardiac cycle. The dynamic annulus area was behaving differently between mildly and severely calcified subgroups (p = 0.02). Furthermore, patients with severe aortic calcification were associated with larger annulus diameters. CONCLUSION: There is a significant variation of annulus area and calcium volume measurement during the cardiac cycle. In our measurements, only the dynamic variation of the annulus area is dependent on the severity of the aortic calcification. For TAVI candidates, the annulus area is significantly larger in mid-systole compared to end-diastole.

Acoustic noise reduction in pseudo-continuous arterial spin labeling (pCASL).

OBJECT: While pseudo-continuous arterial spin labeling (pCASL) is a promising imaging technique to visualize cerebral blood flow, it is also (acoustically) very loud during labeling. In this paper, we reduced the labeling loudness on our scanner by increasing the interval between the RF pulses from the literature standard of 1.0 ms. We also propose recommendations to reduce the loudness on scanners of the same type at other sites. MATERIALS AND METHODS: First, the sound pressure level (SPL) was both simulated and measured as a function of the labeling interval (1.0-1.8 ms) and longitudinal position in the scanner (-10 to +10 cm, relative to isocenter). Subsequently, we selected the labeling interval with the lowest overall SPL for the "SPL-optimized" pCASL sequence. Nine volunteers were scanned to compare raw signal intensity, temporal signal-to-noise ratio (tSNR) and labeling efficiency between the SPL-optimized and the standard PCASL sequence. RESULTS: Sound pressure level measurements on our scanner showed that loudness was reduced by 6.5 dB at the approximate location of the ear by adjusting the labeling interval to 1.4 ms. Furthermore, image quality was not affected, since no significant differences in signal intensity, tSNR and labeling efficiency were observed. CONCLUSION: By increasing the pCASL labeling interval, acoustic noise in the pCASL sequence was reduced with 6.5 dB, while image quality was preserved.

Comparison of in vivo carotid 3.0-T magnetic resonance to B-mode ultrasound imaging and histology in a porcine model.

OBJECTIVES: We compared in vivo 3.0-T magnetic resonance (MR) images of the carotid artery wall in piglets to intima-media thickness measurements of similar carotid segments by B-mode ultrasound (US) and histology to define the corresponding anatomical tissue characteristics and accuracy of carotid MR images. BACKGROUND: Carotid MR is increasingly used for the assessment of cardiovascular risk and cardiovascular drug efficacy. Therefore, determining the anatomical correlate and accuracy of this modality is of major importance. METHODS: In vivo 3.0-T MR and B-mode US scans of the left and right common carotid arteries were performed in 5 piglets (75 to 80 kg). The T(1)-weighted MR images were acquired with a noninterpolated pixel size of 0.25 x 0.25 mm for mean wall area (MWA) and mean wall thickness measurements. The B-mode US measured common carotid intima-media thickness and common carotid diameter. We calculated US MWA using common carotid intima-media thickness and carotid diameter. In histology, the intima and media tissue area was defined as histology MWA. RESULTS: Histology MWA was 4.69 (standard deviation [SD]: 0.95) mm(2), MR MWA was 4.57 (SD: 0.41) mm(2), and US MWA was 4.90 (SD: 0.50) mm(2). The mean difference was 0.12 (SD: 1.11) mm(2) for MR and -0.21 (SD: 1.01) mm(2) for US when compared with histology. Bland-Altman analysis showed no systematic biases between MR, US, or histology. CONCLUSIONS: Absolute values for carotid artery histology, MR, and US measurements are in good agreement, indicating that both 3.0-T MR and B-mode US measurements can visualize the intima and media. Accuracy of 3.0-T MR is comparable to B-mode US. The present findings imply that carotid MR might be a novel asset in cardiovascular disease risk stratification and a valuable surrogate marker in cardiovascular prevention trials.