MRI features associated with acute appendicitis.

OBJECTIVES: To identify MRI features associated with appendicitis. METHODS: Features expected to be associated with appendicitis were recorded in consensus by two expert radiologists on 223 abdominal MRIs in patients with suspected appendicitis. Nine MRI features were studied: appendix diameter >7 mm, appendicolith, peri-appendiceal fat infiltration, peri-appendiceal fluid, absence of gas in the appendix, appendiceal wall destruction, restricted diffusion of the appendiceal wall, lumen or focal fluid collections. Appendicitis was assigned as the final diagnosis in 117/223 patients. Associations between imaging features and appendicitis were evaluated with logistic regression analysis. RESULTS: All investigated features were significantly associated with appendicitis in univariate analysis. Combinations of two and three features were associated with a probability of appendicitis of 88 % and 92 %, respectively. In patients without any of the nine features, appendicitis was present in 2 % of cases. After multivariate analysis, only an appendix diameter >7 mm, peri-appendiceal fat infiltration and restricted diffusion of the appendiceal wall were significantly associated with appendicitis. The probability of appendicitis was 96 % in their presence and 2 % in their absence. CONCLUSIONS: An appendix diameter >7 mm, peri-appendiceal fat infiltration and restricted diffusion of the appendiceal wall have the strongest association with appendicitis on MRI. KEY POINTS: • An enlarged appendix, fat infiltration and restricted diffusion are associated with appendicitis. • One such feature on MRI gives an 88 % probability of appendicitis. • Two features in combination give a probability of appendicitis of 94 %. • Combinations of three features give a probability of appendicitis of 96 %. • The absence of these features almost rules out appendicitis (2 %).

Comparison of imaging strategies with conditional contrast-enhanced CT and unenhanced MR imaging in patients suspected of having appendicitis: a multicenter diagnostic performance study.

PURPOSE: To compare the diagnostic performance of imaging strategies with magnetic resonance (MR) imaging and computed tomographic (CT) imaging in adult patients suspected of having appendicitis. MATERIALS AND METHODS: Institutional review board approval was obtained prior to study initiation, and patients gave written informed consent. In a multicenter diagnostic performance study, adults suspected of having appendicitis were prospectively identified in the emergency department. Consenting patients underwent ultrasonography (US) and subsequent contrast-enhanced CT if US imaging yielded negative or inconclusive results. Additionally, all patients underwent unenhanced MR imaging, with the reader blinded to other findings. An expert panel assigned final diagnosis after 3 months. Diagnostic performance of three imaging strategies was evaluated: conditional CT after US, conditional MR imaging after US, and immediate MR imaging. Sensitivity and specificity were calculated by comparing findings with final diagnosis. RESULTS: Between March and September 2010, 229 US, 115 CT, and 223 MR examinations were performed in 230 patients (median age, 35 years; 40% men). Appendicitis was the final diagnosis in 118 cases. Conditional and immediate MR imaging had sensitivity and specificity comparable to that of conditional CT, which resulted in 3% (three of 118; 95% confidence interval [CI]: 1%, 7%) missed appendicitis, and 8% (10 of 125; 95% CI: 4%, 14%) false-positives. Conditional MR missed appendicitis in 2% (two of 118; 95% CI: 0%, 6%) and generated 10% (13 of 129; 95% CI: 6%, 16%) false-positives. Immediate MR missed 3% (four of 117; 95% CI: 1%, 8%) appendicitis with 6% (seven of 120; 95% CI: 3%, 12%) false-positives. Conditional strategies resulted in more false-positives in women than in men (conditional CT, 17% vs 0%; P = .03; conditional MR, 19% vs 1%; P = .04), wherease immediate MR imaging did not. CONCLUSION: The accuracy of conditional or immediate MR imaging was similar to that of conditional CT in patients suspected of having appendicitis, which implied that strategies with MR imaging may replace conditional CT for appendicitis detection.

Late-onset dementia: structural brain damage and total cerebral blood flow.

PURPOSE: To prospectively compare indicators of structural brain damage and total cerebral blood flow in patients with late-onset dementia, subjects of the same age with optimal cognitive function, and young subjects. MATERIALS AND METHODS: The institutional ethics committee approved the studies, and all participants (or their guardians) gave informed consent. The test group included 17 patients older than 75 years (four men, 13 women; median age, 83 years) and with a diagnosis of dementia according to the criteria of the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition. The control group included 16 subjects (four men, 12 women; median age, 87 years) with optimal cognitive function, who were selected from among 599 elderly subjects enrolled in a population-based follow-up study, and 15 young healthy subjects (seven men, eight women; median age, 29 years). Measurements of intracranial and total brain volumes, structural brain damage, and cerebral blood flow were obtained with magnetic resonance imaging. Mean values were compared with the t test; medians, with the Mann-Whitney U test. RESULTS: Values for total brain volume were significantly smaller in elderly subjects (P < .001) but did not differ significantly between patients with dementia and subjects of the same age with optimal cognitive function (P = .69). Among the elderly, significantly higher scores for number and extent of white matter areas of signal hyperintensity (P = .028) and lower magnetization transfer ratios (P = .016) indicated greater structural brain damage in those with dementia. Cerebral blood flow was 246 mL/min lower (P < .001) in elderly subjects than in young subjects. In patients with dementia, cerebral blood flow was 108 mL/min lower than that in subjects of the same age with optimal cognitive function (551 vs 443 mL/min, P < .001). CONCLUSION: The combined observations of more structural brain damage and lower cerebral blood flow in demented elderly individuals than in subjects of the same age with optimal cognitive function support the hypothesis that vascular factors contribute to dementia in old age.

Age-related changes in normal-appearing brain tissue and white matter hyperintensities: more of the same or something else?

BACKGROUND AND PURPOSE: Cerebral white matter (WM) hyperintensities are a frequent finding in elderly people, and lowering of cerebral magnetization transfer ratio (MTR) has been observed. The aim of this study was to assess the relationship between age-related WM hyperintensities and MTR changes in the brain. METHODS: We performed MR imaging in a group of young subjects, a group of elderly individuals with minimal WM hyperintensities, and a group of elderly individuals with abundant WM hyperintensities. In addition, we performed volumetric MTR analysis of the whole brain and of the normal-appearing WM (NAWM) in these groups. RESULTS: Volumetric MTR parameters differed between elderly and young patients. Mean MTR +/- standard error of the mean (SEM) was 34.0% +/- 0.12% in the young, 33.0% +/- 0.08% in the elderly with minimal WM hyperintensities, 32.8% +/- 0.09%) in the group with abundant WM hyperintensities. Peak height (number of voxels +/- SEM) was 122 +/- 1.2 in the young, 99 +/- 1.5 in the elderly with minimal WM hyperintensities, and 98 +/- 1.6 in the group with abundant WM hyperintensities. Mean MTR of NAWM was lower in the elderly compared with the young (36.7% +/- 0.12%) but did not differ between subjects with minimal (36.0% +/- 0.11%) and those with abundant WM hyperintensities (35.9% +/- 0.13%). CONCLUSION: Our results show that aging gives rise to changes in normal-appearing brain tissue. These changes, which can be detected on magnetization transfer imaging, seem to have no relationship with age-related WM hyperintensities and might have a different etiology.

Basal cerebral blood flow is dependent on the nitric oxide pathway in elderly but not in young healthy men.

OBJECTIVE: Brain perfusion is tightly regulated over a wide range of blood pressures by local regulation of cerebral blood flow (CBF). Ageing is associated with impaired CBF and impaired nitric oxide mediated vasodilator responses. The role of nitric oxide in the regulation of basal CBF in young and older subjects was investigated, using the nitric oxide synthase inhibitor L-NMMA as pharmacological tool. METHODS: We used a gradient echo phase-contrast magnetic resonance imaging technique to investigate the role of nitric oxide in the regulation of cerebral blood flow in young (25+/-7.1 years; n=8) and old (78+/-6.6 years; n=7) volunteers. The study was performed in a double-blinded fashion and consisted of two study days. On one day the effects of the intravenously infused L-NMMA on CBF and blood pressure was measured and on the other day the effects of a matching placebo. RESULTS: Basal CBF was significantly lower in old compared to young subjects (590+/-20 vs 704+/-20 ml/min), while the cerebral vascular resistance (CVR) levels were significantly higher (0.15+/-0.01 (arbitrary units) vs 0.12+/-0.01, respectively). Infusion of L-NMMA significantly increased mean arterial pressure in both groups (2.8+/-1.2 mmHg; p=0.02 in the young and in the old subjects 5.6+/-1.1 mmHg; p<0.001). Infusion of L-NMMA significantly decreased CBF (49+/-12 ml/min; p<0.001) and increased CVR (0.02+/-0.004; p<0.001) in the old subjects but did not significantly influence cerebral circulation in the young subjects. CONCLUSION: We conclude that compared to young subjects, in old people CBF is impaired, and dependent on the intactness of the nitric oxide pathway.

Automatic model-based contour detection and blood flow quantification in small vessels with velocity encoded magnetic resonance imaging.

RATIONALE AND OBJECTIVES: The quantitative assessment of blood flow in peripheral vessels from phase-contrast magnetic resonance imaging studies requires the accurate delineation of vessel contours in cross-sectional magnetic resonance images. The conventional manual segmentation approach is tedious, time-consuming, and leads to significant inter- and intraobserver variabilities. The aim of this study was to verify whether automatic model-based segmentation decreases these problems by fitting a model to the actual blood velocity profile. METHODS: In this study 2 new fully automatic methods (a static and a dynamic approach) were developed and compared with manual analyzes using phantom and in vivo studies of internal carotid and vertebral arteries in healthy volunteers. The automatic segmentation approaches were based on fitting a 3D parabolic velocity model to the actual velocity profiles. In the static method, the velocity profiles were averaged over the complete cardiac cycle, whereas the dynamic method takes into account the velocity data of each cardiac time bin individually. Materials consisted of the magnetic resonance imaging data from 3 straight phantom tubes and the blood velocity profiles of 8 volunteers. RESULTS: For the phantom studies, the automatic dynamic approach performed significantly better than the manual analysis (intraclass correlations [ICC] of 0.62-0.98 and 0.30-0.86, respectively). For the assessment of the total cerebral blood flow in the in vivo studies, the automatic static method performed significantly better than the manual 1 (ICC of 0.98-0.98 and 0.93-0.95, respectively). However, the automatic dynamic method was not significantly better than the manual 1 (ICC = 0.92-0.96) but had the advantage of providing additional parameters. CONCLUSION: Blood flow in magnetic resonance images of small vessels can be assessed accurately, rapidly, and fully automatically using model-based postprocessing by fitting a first approximation of the velocity profile to the actual flow data.

Cerebral hemodynamics and white matter hyperintensities in CADASIL.

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a hereditary small-vessel disease caused by mutations in the NOTCH3 gene on chromosome 19. On magnetic resonance imaging (MRI), subcortical white matter hyperintensities and lacunar infarcts are visualized. It is unknown whether a decrease in cerebral blood flow or cerebrovascular reactivity is primarily responsible for the development of white matter hyperintensities and lacunar infarcts. The authors used phase-contrast MRI in 40 NOTCH3 mutation carriers (mean age 45 +/- 10 years) and 22 nonmutated family members (mean age 39 +/- 12 years), to assess baseline total cerebral blood flow (TCBF) and cerebrovascular reactivity after acetazolamide. Mean baseline TCBF was significantly decreased in NOTCH3 mutation carriers. In young subjects, baseline TCBF was significantly lower than in nonmutation carriers (mean difference 124 mL/min). Furthermore, baseline TCBF did not differ significantly between mutation carriers with minimal and mutation carriers with moderate or severe white matter hyperintensities. No significant difference in mean cerebrovascular reactivity was found between mutation carriers and nonmutation carriers. This study suggests that a decrease in baseline TCBF in NOTCH3 mutation carriers precedes the development of white matter hyperintensities.

MR assessment of cerebral vascular response: a comparison of two methods.

PURPOSE: To compare the results and reproducibility of two MR-based methods of measuring the cerebrovascular response (CVR). MATERIALS AND METHODS: In eight volunteers, CVR was assessed with two MR-based methods upon a challenge with acetazolamide. CVR was assessed by measuring changes in total cerebral blood flow (TCBF) using phase contrast (PC) MRI, and by measuring perfusion MRI. To assess reproducibility the measurements were repeated after 1 week. RESULTS: The average CVR with the PC-MRI method was 46% (SD = 16%), and for perfusion MR the measured CVR was 44% (SD = 16%). The coefficient of variation (COV) for PC-MRI was 28%, while perfusion MR had a COV of 26%. The limits of agreement between the two methods were -49% and 45%, demonstrating a lack of agreement between the two methods in terms of CVR estimation. CONCLUSION: CVR estimates based on PC-MRI and perfusion MRI showed reproducibility but a lack of agreement in healthy volunteers. This lack of agreement can be attributed to the different aspects of the CVR reflected by these methods: TCBF reflects changes in CBF, whereas our perfusion MRI method reflects cerebral blood volume (CBV).

Reproducibility of total cerebral blood flow measurements using phase contrast magnetic resonance imaging.

PURPOSE: To evaluate reproducibility of total cerebral blood flow (CBF) measurements with phase contrast magnetic resonance imaging (pcMRI). MATERIALS AND METHODS: We repeated total CBF measurements in 15 healthy volunteers with and without cardiac triggering, and with and without repositioning. In eight volunteers measurements were performed at two different occasions. In addition, measurement of flow in a phantom was performed to validate MR measurements. RESULTS: A difference of 40.4 ml/minute was found between CBF measurements performed with and without triggering (P < 0.05). For repeated triggered measurements, the coefficient of variation (CV) was 7.1%, and for nontriggered measurements 10.3%. For repeated measurements with repositioning, the CV was 7.1% with and 11.2% without triggering. Repeated measurements at different occasions showed a CV of 8.8%. Comparing measured with real flow in the phantom, the triggered differed 4.9% and the nontriggered 8.3%. CONCLUSION: The findings of this study demonstrate that pcMRI is a reliable method to measure total CBF in terms of both accuracy and reproducibility.

Nitric oxide mediates hypoxia-induced cerebral vasodilation in humans.

Nitric oxide (NO) plays a pivotal role in the regulation of peripheral vascular tone. Its role in the regulation of cerebral vascular tone in humans remains to be elucidated. This study investigates the role of NO in hypoxia-induced cerebral vasodilatation in young healthy volunteers. The effect of the NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA) on the cerebral blood flow (CBF) was assessed during normoxia and during hypoxia (peripheral O(2) saturation 97 and 80%, respectively). Subjects were positioned in a magnetic resonance scanner, breathing normal air (normoxia) or a N(2)-O(2) mixture (hypoxia). The CBF was measured before and after administration of L-NMMA (3 mg/kg) by use of phase-contrast magnetic resonance imaging techniques. Administration of L-NMMA during normoxia did not affect CBF. Hypoxia increased CBF from 1,049 +/- 113 to 1,209 +/- 143 ml/min (P < 0.05). After L-NMMA administration, the augmented CBF returned to baseline (1,050 +/- 161 ml/min; P < 0.05). Similarly, cerebral vascular resistance declined during hypoxia and returned to baseline after administration of L-NMMA (P < 0.05 for both). Use of phase-contrast magnetic resonance imaging shows that hypoxia-induced cerebral vasodilatation in humans is mediated by NO.