Performance of Spectral Photon-Counting Coronary CT Angiography and Comparison with Energy-Integrating-Detector CT: Objective Assessment with Model Observer.

AIMS: To evaluate spectral photon-counting CT's (SPCCT) objective image quality characteristics in vitro, compared with standard-of-care energy-integrating-detector (EID) CT. METHODS: We scanned a thorax phantom with a coronary artery module at 10 mGy on a prototype SPCCT and a clinical dual-layer EID-CT under various conditions of simulated patient size (small, medium, and large). We used filtered back-projection with a soft-tissue kernel. We assessed noise and contrast-dependent spatial resolution with noise power spectra (NPS) and target transfer functions (TTF), respectively. Detectability indices (d') of simulated non-calcified and lipid-rich atherosclerotic plaques were computed using the non-pre-whitening with eye filter model observer. RESULTS: SPCCT provided lower noise magnitude (9-38% lower NPS amplitude) and higher noise frequency peaks (sharper noise texture). Furthermore, SPCCT provided consistently higher spatial resolution (30-33% better TTF10). In the detectability analysis, SPCCT outperformed EID-CT in all investigated conditions, providing superior d'. SPCCT reached almost perfect detectability (AUC ≈ 95%) for simulated 0.5-mm-thick non-calcified plaques (for large-sized patients), whereas EID-CT had lower d' (AUC ≈ 75%). For lipid-rich atherosclerotic plaques, SPCCT achieved 85% AUC vs. 77.5% with EID-CT. CONCLUSIONS: SPCCT outperformed EID-CT in detecting simulated coronary atherosclerosis and might enhance diagnostic accuracy by providing lower noise magnitude, markedly improved spatial resolution, and superior lipid core detectability.

Reduced-iodine-dose dual-energy coronary CT angiography: qualitative and quantitative comparison between virtual monochromatic and polychromatic CT images.

OBJECTIVES: To quantitatively evaluate the impact of virtual monochromatic images (VMI) on reduced-iodine-dose dual-energy coronary computed tomography angiography (CCTA) in terms of coronary lumen segmentation in vitro, and secondly to assess the image quality in vivo, compared with conventional CT obtained with regular iodine dose. MATERIALS AND METHODS: A phantom simulating regular and reduced iodine injection was used to determine the accuracy and precision of lumen area segmentation for various VMI energy levels. We retrospectively included 203 patients from December 2017 to August 2018 (mean age, 51.7 ± 16.8 years) who underwent CCTA using either standard (group A, n = 103) or reduced (group B, n = 100) iodine doses. Conventional images (group A) were qualitatively and quantitatively compared with 55-keV VMI (group B). We recorded the location of venous catheters. RESULTS: In vitro, VMI outperformed conventional CT, with a segmentation accuracy of 0.998 vs. 1.684 mm2, respectively (p < 0.001), and a precision of 0.982 vs. 1.229 mm2, respectively (p < 0.001), in simulated overweight adult subjects. In vivo, the rate of diagnostic CCTA in groups A and B was 88.4% (n = 91/103) vs. 89% (n = 89/100), respectively, and noninferiority of protocol B was inferred. Contrast-to-noise ratios (CNR) of lumen versus fat and muscle were higher in group B (p < 0.001) and comparable for lumen versus calcium (p = 0.423). Venous catheters were more often placed on the forearm or hand in group B (p < 0.001). CONCLUSION: In vitro, low-keV VMI improve vessel area segmentation. In vivo, low-keV VMI allows for a 40% iodine dose and injection rate reduction while maintaining diagnostic image quality and improves the CNR between lumen versus fat and muscle. KEY POINTS: • Dual-energy coronary CT angiography is becoming increasingly available and might help improve patient management. • Compared with regular-iodine-dose coronary CT angiography, reduced-iodine-dose dual-energy CT with low-keV monochromatic image reconstructions performed better in phantom-based vessel cross-sectional segmentation and proved to be noninferior in vivo. • Patients receiving reduced-iodine-dose dual-energy coronary CT angiography often had the venous catheter placed on the forearm or wrist without compromising image quality.

Impact of CT venography added to CT pulmonary angiography for the detection of deep venous thrombosis and relevant incidental CT findings.

OBJECTIVES: To assess the additional diagnostic value of CT venography (CTV) simultaneously performed with CT pulmonary angiography (CTPA) in the context of thromboembolic disease for the detection of deep venous thrombosis (DVT) and other relevant incidental CT findings. MATERIALS AND METHODS: Retrospectively and consecutively, we included all patients referred to our emergency department within the last 24 months for suspected pulmonary embolism (PE) who underwent CTPA combined with CTV. Two radiologists blinded to clinical information and results independently analysed CTV images in the context of DVT of the lower extremities and other, unsuspected abdominal/pelvic findings. These latter were classified as relevant with therapeutic consequences or irrelevant. One radiologist reviewed patient clinical records. Inter-observer agreement for DVT detection was calculated. RESULTS: Of 696 patients, 119 had PE (17.1%) and 54 had DVT (7.8%), 16 (2.3%) of them without concomitant PE. Inter-observer agreement between the two readers was substantial (kappa = 0.78). CTV examinations led to diagnosis of relevant incidental abdominal/pelvic findings in 40 (5.7%) patients, including 11 with new malignant tumours, and 8 with progressive metastatic disease. The evaluated clinical and biological risk factors were not significantly associated with the presence of relevant incidental findings. CTV changed therapeutic management in 29 patients (4.3%): 15 had DVTs without PE, and 14 had abdominal/pelvic findings with therapeutic consequences. CONCLUSION: CTV simultaneously performed with CTPA offers limited incremental value for detecting DVT. It may reveal other relevant findings leading to therapeutic changes, but the low rate does not justify screening patients with suspected PE.

Re: Does Gadoterate Meglumine Cause Gadolinium Retention in the Brain of Children? A Case-Control Study.

LEVEL OF EVIDENCE: 5 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2020;52:636-637.

"Dark-blood" dual-energy computed tomography angiography for thoracic aortic wall imaging.

OBJECTIVES: To assess the capability of a newly developed material decomposition method from contrast-enhanced dual-energy CT images, aiming to better visualize the aortic wall and aortic intramural hematoma (IMH), compared with true non-contrast (TNC) CT. MATERIALS AND METHODS: Twenty-two patients (11 women; mean age, 61 ± 20 years) with acute chest pain underwent 25 dual-layer non-contrast and contrast-enhanced CT. CT-angiography images were retrospectively processed using two-material decomposition analysis, where we defined the first material as the content of a region of interest placed in the ascending aorta for each patient, and the second material as water. Two independent radiologists assessed the images from the second material termed "dark-blood" images and the TNC images regarding contrast-to-noise ratio (CNR) between the wall and the lumen, diagnostic quality regarding the presence of aortic wall thickening, and the inner/outer vessel wall conspicuity. RESULTS: Diagnostic quality scores in normal aortic segments were 0.9 ± 0.3 and 2.7 ± 0.6 (p < 0.001) and wall conspicuity scores were 0.7 ± 0.5 and 1.8 ± 0.3 (p < 0.001) on TNC and dark-blood images, respectively. In aortic segments with IMH, diagnostic quality scores were 1.7 ± 0.5 and 2.4 ± 0.6 (p < 0.001) and wall conspicuity scores were 0.7 ± 0.7 and 1.8 ± 0.3 (p < 0.001) on TNC and dark-blood images, respectively. In normal aortic segments, CNRs were 0.3 ± 0.2 and 2.8 ± 0.9 on TNC and dark-blood images, respectively (p < 0.001). In aortic segments with IMH, CNRs were 0.3 ± 0.2 and 4.0 ± 1.0 on TNC and dark-blood images, respectively (p < 0.001). CONCLUSIONS: Compared with true non-contrast CT, dark-blood material decomposition maps enhance quantitative and qualitative image quality for the assessment of normal aortic wall and IMH. KEY POINTS: • Current dual-energy CT-angiography provides virtual non-contrast and bright-blood images. • Dark-blood images represent a new way to assess the vascular wall structure with dual-energy CT and can improve the lumen-to-wall contrast compared with true non-contrast CT. • This dual-energy CT material decomposition method is likely to improve contrast resolution in other applications as well, taking advantage of the high spatial resolution of CT.

Pulmonary Lymphangitic Carcinomatosis: Diagnostic Performance of High-Resolution CT and 18F-FDG PET/CT in Correlation with Clinical Pathologic Outcome.

The rationale of this study was to investigate the performance of high-resolution CT (HRCT) versus 18F-FDG PET/CT for the diagnosis of pulmonary lymphangitic carcinomatosis (PLC). Methods: In this retrospective institution-approved study, 94 patients addressed for initial staging of lung cancer with suspicion of PLC were included. Using double-blind analysis, we assessed the presence of signs favoring PLC on HRCT (smooth or nodular septal lines, subpleural nodularity, peribronchovascular thickening, satellite nodules, lymph node enlargement, and pleural effusion). 18F-FDG PET/CT images were reviewed to qualitatively evaluate peritumoral uptake and to quantify tracer uptake in the tumoral and peritumoral areas. Histology performed on surgical specimens served as the gold standard for all patients. Results: Among 94 included patients, 73% (69/94) had histologically confirmed PLC. Peribronchovascular thickening, lymph node involvement, and increased peritumoral uptake were more often present in patients with PLC (P < 0.009). Metabolic variables, including tumor SUVmax, SUVmean, metabolic tumor volume, and total lesion glycolysis, as well as peritumoral SUVmax, SUVmean, and their respective ratios to background, were significantly higher in the PLC group than in the non-PLC group (P ≤ 0.0039). Sensitivity, specificity, and area under the receiver-operating-characteristic curve for peribronchovascular thickening (69%, 83%, and 0.76, respectively; 95% confidence interval [95%CI], 0.67-0.85) and increased peritumoral uptake (94%, 84%, and 0.89, respectively; 95%CI, 0.81-0.97) were similar (P = 0.054). For detecting PLC, sensitivity, specificity, and area under the receiver-operating-characteristic curve were significantly higher, at 97%, 92%, and 0.98, respectively (95%CI, 0.96-1.00), for peritumoral SUVmax and 94%, 88%, and 0.96, respectively (95%CI, 0.92-1.00), for peritumoral SUVmean (all P ≤ 0.025). Conclusion: Qualitative evaluation of 18F-FDG PET/CT and HRCT perform similarly for the diagnosis of PLC, with both being outperformed by 18F-FDG PET/CT quantitative parameters.

Pulmonary embolism during pregnancy: a 17-year single-center retrospective MDCT pulmonary angiography study.

OBJECTIVES: To determine the prevalence of pulmonary embolism (PE) and alternative diagnoses detected by computed tomography pulmonary angiography (CTPA) in pregnant women; and to assess changes over time regarding radiation dose, technical quality, and examination frequency. MATERIALS AND METHODS: This retrospective study included all pregnant women referred for CTPA due to clinically suspected PE over 17 years. Two blinded radiologists reviewed the CTPAs in consensus with regard to PE, alternative diagnoses, and technical quality. We retrieved patient data regarding radiation dose metrics and associated clinical and laboratory parameters. Subgroup comparisons were performed (Wilcoxon and Kruskal-Wallis tests). RESULTS: Of the 237 identified patients, 8 (3.3%) were excluded due to inadequate technical CTPA quality, and 229 patients were analyzed (mean age, 31.7 years; mean gestational age, 28 ± 7 weeks). The four different CT systems used over the study period had similar technical quality (p = 0.28). Of 229 patients 16 (7%) patients had PE, 144 (62.9%) had no abnormal findings, and 69 (30.1%) had an alternative diagnosis (consolidation, other pulmonary opacities, pleural effusion, and basal atelectasis). Gestational age, symptoms, and D-dimer levels were not significantly different between patients with or without PE (p > 0.05). Over time, radiation dose exposure decreased by 30% (p < 0.001), while the number of annual examinations increased by > 4-folds. CONCLUSIONS: In pregnant women, CTPA rarely indicates PE and more often shows alternative diagnoses. Over 17 years, the use of CTPA in pregnancy has notably increased, while the radiation dose exposure has decreased by one third. KEY POINTS: • The use of CTPA in pregnancy has steadily risen over the last 17 years • In pregnant women, CTPA rarely reveals PE and more often shows alternative diagnoses • Recent technical improvements have substantially decreased the radiation dose exposure inherent in CTPA without reducing diagnostic image quality.

Age, But Not Repeated Exposure to Gadoterate Meglumine, Is Associated With T1- and T2-Weighted Signal Intensity Changes in the Deep Brain Nuclei of Pediatric Patients.

OBJECTIVES: Current findings on gadolinium deposition in the pediatric brain due to repeated exposure to macrocyclic contrast agents are inconclusive and possibly confounded by brain maturation processes. We evaluated the longitudinal effects of repeated gadoterate meglumine exposure (Dotarem; Guerbet, Villepinte, France) on the T1- and T2-weighted signal intensity (SI) in pediatric patients, and assessed the magnitude of age-related increase in T1-weighted (and decrease in T2-weighted) SI in a control cohort without prior gadolinium exposure. MATERIALS AND METHODS: In this retrospective, double-cohort study, magnetic resonance imaging (MRI) data of 24 patients (0.7-16.4 years, M = 5.74, SD = 4.15) who received at least 10 doses of exclusively gadoterate meglumine were included in the longitudinal study. The MRI data of 190 controls (age range, 1-20 years; 10 patients/bin; bin width, 1 year) without any prior gadolinium-based contrast exposure were included in the control, cross-sectional study to assess the age-dependent SI changes in the regions of interest (ROIs). We measured SI (native), T1-weighted gradient echo, and T2-weighted fast spin-echo of 12 deep brain nuclei. The ROIs were measured at each of the first 11 MRI examinations of the contrast-exposed patients and in the control subject's MRI. Regions of interest's SIs, normalized by the pons, were analyzed with mixed effects models, accounting for the potential confounding factors, such as radiotherapy and chemotherapy. RESULTS: The number of gadoterate meglumine administrations had no effect on the SI increase in any of the ROIs (all P > 0.05), but age significantly correlated with increased SI in T1-weighted globus pallidus (GP; P < 0.01) and caudate (P < 0.05), and with decreased SI in T2-weighted GP (P < 0.001) and dentate nucleus (P < 0.005) in the contrast-exposed group. The cross-sectional analyses of the control cohort showed a significant age-dependent T1-weighted SI increase in multiple ROIs, including the GP and caudate, and decrease in the T2-weighted GP and dentate nucleus (P < 0.05). CONCLUSIONS: Repeated exposure to gadoterate meglumine was not associated with brain hyperintensity in the pediatric patients, whereas age importantly contributed to the SI changes in several deep brain nuclei.

Spatiotemporal Pattern of Gadodiamide-Related T1 Hyperintensity Increase Within the Deep Brain Nuclei.

OBJECTIVES: The purpose of the study was to systematically evaluate the precise spatial and temporal pattern of gadolinium-related changes in T1-weighted signal intensity on unenhanced magnetic resonance (MR) images, occurring in the deep brain nuclei of adult patients exposed to at least 10 consecutive doses of gadodiamide. MATERIALS AND METHODS: In this monocentric retrospective longitudinal study, we analyzed the brain MR images of 30 patients (12 women, 18 men; mean age, 43 ± 11.6 years) acquired between December 1998 and March 2008. We drew the regions of interest in the dentate nucleus, globus pallidus, putamen, pulvinar, ventral posterior nucleus of the thalamus, superior colliculus, substantia nigra, and white matter on unenhanced T1-weighted images. Each region of interest's mean signal intensity was normalized by the mean intensity of the pons. The normalized signal intensities were measured at the baseline before first gadodiamide administration and at each of 10 successive MR imaging examinations. We used linear mixed effects models to analyze the data. RESULTS: We observed a significant linear increase of signal intensity ratios across 10 successive gadodiamide administrations (all basal nuclei were significant at P < 0.001, except the ventral posterior thalamus, where P < 0.05), with the fastest signal intensity increase in the dentate nucleus (B = 0.010), followed by the globus pallidus (B = 0.0068), putamen (B = 0.0063), pulvinar (B = 0.0062), superior colliculus (B = 0.0057), substantia nigra (B = 0.0034), and ventral posterior nucleus of the thalamus (B = 0.0031). No significant signal increase was observed in the white matter (P > 0.05). CONCLUSIONS: Multiple consecutive administration of gadodiamide is associated with an increase in T1-weighted hypersignal on the unenhanced scans, displaying a gradual and nonuniform pattern across different deep brain nuclei, including the ventral posterior thalamus, which was used as a reference tissue in previous studies.

Factors Associated With Focal Computed Tomographic Perfusion Abnormalities in Supratentorial Transient Ischemic Attacks.

BACKGROUND AND PURPOSE: Computed tomographic perfusion (CTP) is useful in diagnosis of patients with transient focal neurological symptoms. In acute imaging of patients with a suspected transient ischemic attack (TIA), it remains unclear which patients develop focal perfusion abnormalities (FPA), that is, hypoperfusion or hyperperfusion. We aimed at determining independent factors associated with FPA in patients with supratentorial TIAs. METHODS: We prospectively collected consecutive patients with supratentorial TIAs defined by the traditional time-based definition who underwent CTP within 24 hours of symptom onset. We recorded demographics, risk factors, clinical features, severity, and timing from onset. We documented the Age, Blood Pressure, Clinical Features, Duration, and Diabetes (ABCD2) scores, vascular territories, and presence of relevant arterial pathology. Variables were tested for an association with FPA with univariate and multivariate analyses. RESULTS: A hundred and ten of 265 patients (42%) with supratentorial TIAs had FPA on CTP. Acute noncontrast computed tomography showed early ischemic lesions in 6%, and acute/subacute magnetic resonance imaging was pathological in 52 of the 109 cases (47.7%) where it was performed. Clinical factors associated with FPA were high-admission National Institutes of Health Stroke Scale (odds ratio [OR], 1.22), right hemispheric TIA (OR, 3.09), and cardioembolic mechanism (OR, 2.19). Persistence of symptoms during CTP (OR, 2.59), shorter duration of TIA (OR, 0.93), major intracranial arterial pathology (OR, 12.5), and extracranial arterial occlusion (OR, 7.44) were also associated with FPA. CONCLUSIONS: Supratentorial TIAs are often associated with FPA in CTP, even after symptom resolution. FPAs are frequent in severe TIAs and those associated with cardioembolism or specific arterial pathologies. These findings can help clinicians in accurate diagnosis of TIA and its underlying mechanisms.

Detection and Viability of Colorectal Liver Metastases After Neoadjuvant Chemotherapy: A Multiparametric PET/CT-MRI Study.

PURPOSE: The aim of this study was to compare combined gadolinium-ethoxybenzyl-diethylenetriamine-pentaacetic acid (Gd-EOB-DTPA)-enhanced and diffusion-weighted (DW) MRI with IV contrast-enhanced F-FDG PET/CT to detect and assess the viability of colorectal liver metastases (CLMs) after neoadjuvant chemotherapy (NAC). PATIENTS AND METHODS: After NAC, 45 patients with CLMs were prospectively enrolled and underwent combined Gd-EOB-DTPA-enhanced and DW-MRI and contrast-enhanced F-FDG PET/CT. Forty patients subsequently underwent surgery based on intraoperative ultrasound, which served as the reference standard for the presence of CLMs. The number of metastases detected by each technique was then compared. In 69 resected metastases, the SUVmean and SUVmax, mean and maximum target-to-background ratio (TBR), total lesion glycolysis, metabolic tumor volume, and mean and minimum apparent diffusion coefficient (ADC) were examined to identify correlations with the corresponding tumor viability (TV) determined from histological specimens. RESULTS: Intraoperative ultrasound revealed 153 CLMs, 122 of which were resected. The detection rate of MRI and contrast-enhanced F-FDG PET/CT were similar (P = 0.61). The SUVmax and minimum ADC were negatively correlated (r = -0.34, P = 0.005) on preoperative imaging after NAC. However, TV was significantly correlated with the maximum TBR (r = 0.33, P = 0.006) and mean TBR (r = 0.37, P = 0.002), but not with the minimum ADC (r = -0.02, P = 0.9) or mean ADC (r = 0.01, P = 0.9). CONCLUSIONS: Combined Gd-EOB-DTPA-enhanced and DW-MRI and contrast-enhanced F-FDG PET/CT allow confident detection of CLMs, but only F-FDG PET metrics are associated with TV after NAC.

Severe pelvic injury: vascular lesions detected by ante- and post-mortem contrast medium-enhanced CT and associations with pelvic fractures.

OBJECTIVES: The objectives of this study were to compare arterial and venous contrast medium extravasation in severe pelvic injury detected by ante- and post-mortem multi-detector CT (MDCT) and determine whether vascular injury is associated with certain types of pelvic fracture. METHODS: We retrospectively included two different cohorts of blunt pelvic trauma with contrast medium extravasation shown by MDCT. The first group comprised 49 polytrauma patients; the second included 45 dead bodies undergoing multi-phase post-mortem CT-angiography (MPMCTA). Two radiologists jointly reviewed each examination concerning type, site of bleeding and pattern of underlying pelvic ring fracture. RESULTS: All 49 polytrauma patients demonstrated arterial bleeding, immediately undergoing subsequent angiography; 42 (85%) had pelvic fractures, but no venous bleeding was disclosed. MPMCTA of 45 bodies revealed arterial (n = 33, 73%) and venous (n = 35, 78%) bleeding and pelvic fractures (n = 41, 91%). Pelvic fracture locations were significantly correlated with ten arterial and six venous bleeding sites in dead bodies, with five arterial bleeding sites in polytrauma patients. In dead bodies, arterial haemorrhage was significantly correlated with the severity of pelvic fracture according to Tile classification (p = 0.01), unlike venous bleeding (p = 0.34). CONCLUSIONS: In severe pelvic injury, certain acute bleeding sites were significantly correlated with underlying pelvic fracture locations. MPMCTA revealed more venous lesions than MDCT in polytrauma patients. Future investigations should evaluate the proportional contribution of venous bleeding to overall pelvic haemorrhage as well as its clinical significance.

Clinical significance of pneumatosis intestinalis - correlation of MDCT-findings with treatment and outcome.

OBJECTIVES: To evaluate the clinical significance of pneumatosis intestinalis (PI) including the influence on treatment and outcome. METHOD AND MATERIALS: Two radiologists jointly reviewed MDCT-examinations of 149 consecutive emergency patients (53 women, mean age 64, range 21-95) with PI of the stomach (n = 4), small (n = 68) and/or large bowel (n = 96). PI extension, distribution and possibly associated porto-mesenteric venous gas (PMVG) were correlated with other MDCT-findings, risk factors, clinical management, laboratory, histopathology, final diagnosis and outcome. RESULTS: The most frequent cause of PI was intestinal ischemia (n = 80,53.7 %), followed by infection (n = 18,12.1 %), obstructive (n = 12,8.1 %) and non-obstructive (n = 10,6.7 %) bowel dilatation, unknown aetiologies (n = 8,5.4 %), drugs (n = 8,5.4 %), inflammation (n = 7,4.7 %), and others (n = 6,4 %). Neither PI distribution nor extension significantly correlated with underlying ischemia. Overall mortality was 41.6 % (n = 62), mostly related to intestinal ischemia (p = 0.003). Associated PMVG significantly correlated with underlying ischemia (p = 0.009), as did the anatomical distribution of PMVG (p = 0.015). Decreased mural contrast-enhancement was the only other MDCT-feature significantly associated with ischemia (p p < 0.001). Elevated white blood count significantly correlated with ischemia (p = 0.03). CONCLUSION: In emergency patients, ischemia remains the most common aetiology of PI, showing the highest mortality. PI with associated PMVG is an alerting sign. PI together with decreased mural contrast-enhancement indicates underlying ischemia. KEY POINTS: • In emergency patients, PI may be caused by various disorders. • Intestinal ischemia remains the most common cause of PI in acute situations. • PI associated with decreased mural contrast-enhancement indicates acute intestinal ischemia. • PI associated with PMVG should alert the radiologist to possible underlying ischemia.

Adaptive filtering methods for identifying cross-frequency couplings in human EEG.

Oscillations have been increasingly recognized as a core property of neural responses that contribute to spontaneous, induced, and evoked activities within and between individual neurons and neural ensembles. They are considered as a prominent mechanism for information processing within and communication between brain areas. More recently, it has been proposed that interactions between periodic components at different frequencies, known as cross-frequency couplings, may support the integration of neuronal oscillations at different temporal and spatial scales. The present study details methods based on an adaptive frequency tracking approach that improve the quantification and statistical analysis of oscillatory components and cross-frequency couplings. This approach allows for time-varying instantaneous frequency, which is particularly important when measuring phase interactions between components. We compared this adaptive approach to traditional band-pass filters in their measurement of phase-amplitude and phase-phase cross-frequency couplings. Evaluations were performed with synthetic signals and EEG data recorded from healthy humans performing an illusory contour discrimination task. First, the synthetic signals in conjunction with Monte Carlo simulations highlighted two desirable features of the proposed algorithm vs. classical filter-bank approaches: resilience to broad-band noise and oscillatory interference. Second, the analyses with real EEG signals revealed statistically more robust effects (i.e. improved sensitivity) when using an adaptive frequency tracking framework, particularly when identifying phase-amplitude couplings. This was further confirmed after generating surrogate signals from the real EEG data. Adaptive frequency tracking appears to improve the measurements of cross-frequency couplings through precise extraction of neuronal oscillations.

Anorectal Malformations: Finding the Pathway out of the Labyrinth.

Anorectal malformations (ARMs) are a complex group of congenital anomalies involving the distal anus and rectum, as well as the urinary and genital tracts in a significant number of cases. Most ARMs result from abnormal development of the urorectal septum in early fetal life. In most cases, the anus is not perforated and the distal enteric component ends blindly (atresia) or as a fistula into the urinary tract, genital tract, or perineum. ARMs are also present in a great number of syndromes and associations of congenital anomalies. The classification of ARMs is mainly based on the position of the rectal pouch relative to the puborectal sling, the presence or absence of fistulas, and the types and locations of the fistulas. All of this information is crucial in determining the most appropriate surgical approach for each case. Imaging studies play a key role in evaluation and classification of ARMs. In neonates, clinical and radiologic examinations in the first 3 days of life help determine the type of ARM and the need for early colostomy. In older children, preoperative pelvic magnetic resonance imaging is the most efficient diagnostic method for evaluating the size, morphology, and grade of development of the sphincteric musculature.

Multidetector CT features of mesenteric vein thrombosis.

Mesenteric vein thrombosis (MVT) accounts for 5%-15% of all mesenteric ischemic events and is classified as either primary or secondary. Primary MVT is idiopathic, whereas secondary MVT can result from a variety of underlying diseases and risk factors, including primary hypercoagulable states or prothrombotic disorders, myeloproliferative neoplasms, cancer (most frequently of the pancreas or liver), diverse inflammatory conditions, recent surgery, portal hypertension, and miscellaneous causes such as oral contraceptives or pregnancy. Clinical symptoms of MVT are rather nonspecific and are mainly characterized by abdominal pain. The mortality rate for MVT remains high, since even now the diagnosis is often delayed. Multidetector computed tomography (CT) is the modality of choice in this context. Although venous bowel ischemia occurs only infrequently with MVT, radiologists should be familiar with its multidetector CT features. Familiarity with the possible causes of MVT, the underlying pathogenic mechanisms associated with MVT, and the correlation between multidetector CT features and these pathogenic mechanisms is necessary to optimize medical management and improve patient care.

Interobserver and intraobserver variability of the apparent diffusion coefficient in treated malignant hepatic lesions on a 3.0T machine: measurements in the whole lesion versus in the area with the most restricted diffusion.

PURPOSE: To assess the inter/intraobserver variability of apparent diffusion coefficient (ADC) measurements in treated hepatic lesions and to compare ADC measurements in the whole lesion and in the area with the most restricted diffusion (MRDA). MATERIALS AND METHODS: Twenty-five patients with treated malignant liver lesions were examined on a 3.0T machine. After agreeing on the best ADC image, two readers independently measured the ADC values in the whole lesion and in the MRDA. These measurements were repeated 1 month later. The Bland-Altman method, Spearman correlation coefficients, and the Wilcoxon signed-rank test were used to evaluate the measurements. RESULTS: Interobserver variability for ADC measurements in the whole lesion and in the MRDA was 0.17 x 10(-3) mm(2)/s [-0.17, +0.17] and 0.43 x 10(-3) mm(2)/s [-0.45, +0.41], respectively. Intraobserver limits of agreement could be as low as [-0.10, +0.12] 10(-3) mm(2)/s and [-0.20, +0.33] 10(-3) mm(2)/s for measurements in the whole lesion and in the MRDA, respectively. CONCLUSION: A limited variability in ADC measurements does exist, and it should be considered when interpreting ADC values of hepatic malignancies. This is especially true for the measurements of the minimal ADC.

Perceptual and semantic contributions to repetition priming of environmental sounds.

Repetition of environmental sounds, like their visual counterparts, can facilitate behavior and modulate neural responses, exemplifying plasticity in how auditory objects are represented or accessed. It remains controversial whether such repetition priming/suppression involves solely plasticity based on acoustic features and/or also access to semantic features. To evaluate contributions of physical and semantic features in eliciting repetition-induced plasticity, the present functional magnetic resonance imaging (fMRI) study repeated either identical or different exemplars of the initially presented object; reasoning that identical exemplars share both physical and semantic features, whereas different exemplars share only semantic features. Participants performed a living/man-made categorization task while being scanned at 3T. Repeated stimuli of both types significantly facilitated reaction times versus initial presentations, demonstrating perceptual and semantic repetition priming. There was also repetition suppression of fMRI activity within overlapping temporal, premotor, and prefrontal regions of the auditory "what" pathway. Importantly, the magnitude of suppression effects was equivalent for both physically identical and semantically related exemplars. That the degree of repetition suppression was irrespective of whether or not both perceptual and semantic information was repeated is suggestive of a degree of acoustically independent semantic analysis in how object representations are maintained and retrieved.

Adaptive tracking of EEG oscillations.

Neuronal oscillations are an important aspect of EEG recordings. These oscillations are supposed to be involved in several cognitive mechanisms. For instance, oscillatory activity is considered a key component for the top-down control of perception. However, measuring this activity and its influence requires precise extraction of frequency components. This processing is not straightforward. Particularly, difficulties with extracting oscillations arise due to their time-varying characteristics. Moreover, when phase information is needed, it is of the utmost importance to extract narrow-band signals. This paper presents a novel method using adaptive filters for tracking and extracting these time-varying oscillations. This scheme is designed to maximize the oscillatory behavior at the output of the adaptive filter. It is then capable of tracking an oscillation and describing its temporal evolution even during low amplitude time segments. Moreover, this method can be extended in order to track several oscillations simultaneously and to use multiple signals. These two extensions are particularly relevant in the framework of EEG data processing, where oscillations are active at the same time in different frequency bands and signals are recorded with multiple sensors. The presented tracking scheme is first tested with synthetic signals in order to highlight its capabilities. Then it is applied to data recorded during a visual shape discrimination experiment for assessing its usefulness during EEG processing and in detecting functionally relevant changes. This method is an interesting additional processing step for providing alternative information compared to classical time-frequency analyses and for improving the detection and analysis of cross-frequency couplings.

Methods for determining frequency- and region-dependent relationships between estimated LFPs and BOLD responses in humans.

The relationship between electrophysiological and functional magnetic resonance imaging (fMRI) signals remains poorly understood. To date, studies have required invasive methods and have been limited to single functional regions and thus cannot account for possible variations across brain regions. Here we present a method that uses fMRI data and singe-trial electroencephalography (EEG) analyses to assess the spatial and spectral dependencies between the blood-oxygenation-level-dependent (BOLD) responses and the noninvasively estimated local field potentials (eLFPs) over a wide range of frequencies (0-256 Hz) throughout the entire brain volume. This method was applied in a study where human subjects completed separate fMRI and EEG sessions while performing a passive visual task. Intracranial LFPs were estimated from the scalp-recorded data using the ELECTRA source model. We compared statistical images from BOLD signals with statistical images of each frequency of the eLFPs. In agreement with previous studies in animals, we found a significant correspondence between LFP and BOLD statistical images in the gamma band (44-78 Hz) within primary visual cortices. In addition, significant correspondence was observed at low frequencies (<14 Hz) and also at very high frequencies (>100 Hz). Effects within extrastriate visual areas showed a different correspondence that not only included those frequency ranges observed in primary cortices but also additional frequencies. Results therefore suggest that the relationship between electrophysiological and hemodynamic signals thus might vary both as a function of frequency and anatomical region.