Components of acquisition-to-acquisition variance in continuous arterial spin labelling (CASL) imaging.

BACKGROUND: Images of perfusion estimates obtained with the continuous arterial spin labelling technique are characterized by variation between single acquisitions. Little is known about the spatial determinants of this variation during the acquisition process and their impact on voxel-by-voxel estimates of effects. RESULTS: We show here that the spatial patterns of covariance between voxels arising during the acquisition of these images uncover distinct mechanisms through which this variance arises: through variation in global perfusion levels; through the action of large vessels and other, less well characterized, large anatomical structures; and through the effect of noisy areas such as the edges of the brain. CONCLUSIONS: Knowledge of these covariance patterns is important to experimenters for a correct interpretation of findings, especially for studies where relatively few acquisitions are made.

Baseline brain perfusion and the serotonin transporter promoter polymorphism.

BACKGROUND: The serotonin transporter length repeat polymorphism (5-HTTLPR) in the promoter region of the serotonin transporter gene (SLC6A4) has been associated in healthy subjects with changes in basal perfusion levels in the limbic system and ventral prefrontal areas, regions involved in the pathophysiology of depression and anxiety, suggesting the existence of a neurobiological trait predisposing to these disorders. We reassess the findings of an increased baseline perfusion in the amygdala and ventral prefrontal areas in healthy carriers of the risk genotype in a much larger sample than in previous studies. METHODS: A cohort of 183 healthy European individuals underwent perfusion imaging with continuous arterial spin-labeling (CASL) while resting quietly in the scanner for 8 minutes. Participants were genotyped to assess the occurrence of the short allele and the Lg and La variants of the long repeat. RESULTS: No association between the 5-HTTLPR polymorphism and baseline brain perfusion was detected in the regions of interest or elsewhere in the brain. In the amygdala, variability in baseline perfusion was explained in large part by global cerebral flow levels (between 50% and 55%), in minor part by sex (between 4% and 5%), but not by genotype (less than .5%). Power analyses showed that the study was of sufficient size to be informative. CONCLUSIONS: The findings did not confirm the existence of a biological marker of the effect of 5-HTTLPR polymorphism in the amygdala or in the orbitofrontal cortex.

Components of variance in brain perfusion and the design of studies of individual differences: the baseline study.

Simple baseline studies correlate average perfusion levels measured at rest with individual variables, or contrast subject groups as in case-control studies. In this methodological work, we summarize some formal properties of the design of these studies, and investigate the sources of variance that characterize data acquired with the arterial spin labeling technique, with the purpose of alerting users to the main sources of variation that determine background variance and affect the power of statistical tests. This design typology is characterized by two variance components: between acquisitions and between subjects. We show that variation between acquisitions is affected by the presence of large vessels and venous sinuses, with potential adverse effects especially in the temporal and insular regions, and provide maps of the number of acquisitions or subjects required to reach the desired estimate precision. Furthermore, we show that the largest source of variation between subjects is captured by global perfusion levels, and can in principle be removed by adjusting the data. Significance levels, however, are not always only improved by the adjustment procedure; we provide an example in the correlation with age, and attempt to explain the consequences of the adjustment with the help of a principal component analysis of the data. We also show the existence of variation between subjects in the perfusion in the territory of the posterior cerebral artery and in hemispheric asymmetry.

Baseline brain perfusion and working memory capacity: a neuroimaging study.

Early studies of rest cerebral metabolism and perfusion reported no association with intellectual capacity. We revisit this issue using a larger sample (N=146) and a continuous arterial spin labeling technique to measure perfusion, and working memory capacity as a measure of intellectual capacity. In the cortex, working memory capacity correlated diffusely and negatively with perfusion. This negative association was more marked in the prefrontal and temporal cortex of the left hemisphere. However, there were also weak positive correlations in the auditory areas, accompanied by analogous correlations in all other areas associated with sensory modalities, with a preference for right lateralization. These findings are discussed in terms of the cortical and vascular organization of the brain.

Preoperative and postoperative quality of life in patients with familial adenomatous polyposis.

PURPOSE: This study was designed to prospectively examine functional outcome, quality of life, and patients' personal experiences and adjustment to functional changes during the first year after prophylactic surgery. METHODS: Twenty-one consecutive patients with familial adenomatous polyposis were examined before proctocolectomy (T0), on ileostomy reversal (T1), and 6 (T2) and 12 months (T3) after surgery by means of standardized questionnaires and interviews. RESULTS: Average physical and mental health declined profoundly after proctocolectomy, followed by a steady improvement after 6 and 12 months. The majority of patients reported the ileostomy period as particularly distressing. After one year, 75 percent of patients reported complete recovery in terms of physical, emotional, and social functioning, whereas one-quarter of patients did not regain their former level of functioning. Despite substantial improvement in pouch functions, functional impairment persists because of frequent bowel movements, resulting mainly in restricted social activities. Ten percent of patients reported impaired sex life, irrespective of gender. CONCLUSIONS: The majority of patients with familial adenomatous polyposis were found to adjust favorably to functional impairment while maintaining satisfactory quality of life. Complementing standardized quality of life measures by patients' personal experiences may help to identify vulnerable patients in need of psychosocial support.