Real-time motion correction in navigator-gated free-breathing double-oblique submillimeter 3D right coronary artery magnetic resonance angiography.

RATIONALE AND OBJECTIVES: The purpose of this study was the investigation of the impact of real-time adaptive motion correction on image quality in navigator-gated, free-breathing, double-oblique three-dimensional (3D) submillimeter right coronary magnetic resonance angiography (MRA). MATERIALS AND METHODS: Free-breathing 3D right coronary MRA with real-time navigator technology was performed in 10 healthy adult subjects with an in-plane spatial resolution of 700 x 700 microm. Identical double-oblique coronary MR-angiograms were performed with navigator gating alone and combined navigator gating and real-time adaptive motion correction. Quantitative objective parameters of contrast-to-noise ratio (CNR) and vessel sharpness and subjective image quality scores were compared. RESULTS: Superior vessel sharpness, increased CNR, and superior image quality scores were found with combined navigator gating and real-time adaptive motion correction (vs. navigator gating alone; P < 0.01 for all comparisons). CONCLUSION: Real-time adaptive motion correction objectively and subjectively improves image quality in 3D navigator-gated free-breathing double-oblique submillimeter right coronary MRA.

Impact of bulk cardiac motion on right coronary MR angiography and vessel wall imaging.

The purpose of this study was to investigate the impact of in-plane coronary artery motion on coronary magnetic resonance angiography (MRA) and coronary MR vessel wall imaging. Free-breathing, navigator-gated, 3D-segmented k-space turbo field echo ((TFE)/echo-planar imaging (EPI)) coronary MRA and 2D fast spin-echo coronary vessel wall imaging of the right coronary artery (RCA) were performed in 15 healthy adult subjects. Images were acquired at two different diastolic time periods in each subject: 1) during a subject-specific diastasis period (in-plane velocity <4 cm/second) identified from analysis of in-plane coronary artery motion, and 2) using a diastolic trigger delay based on a previously implemented heart-rate-dependent empirical formula. RCA vessel wall imaging was only feasible with subject-specific middiastolic acquisition, while the coronary wall could not be identified with the heart-rate-dependent formula. For coronary MRA, RCA border definition was improved by 13% (P < 0.001) with the use of subject-specific trigger delay (vs. heart-rate-dependent delay). Subject-specific middiastolic image acquisition improves 3D TFE/EPI coronary MRA, and is critical for RCA vessel wall imaging.

Respiratory motion artifact suppression in diffusion-weighted MR imaging of the spine.

Diffusion-weighted spin-echo imaging of the spine has been successfully implemented for differentiation of benign fracture edema and tumor infiltration of the vertebral body. Nevertheless, this technique still suffers from insufficient image quality in numerous patients due to motion artifacts. The aim of this study was to investigate the impact of variable respiratory motion artifact suppression techniques on image quality in diffusion-weighted spin-echo imaging of the spine. In addition to phase-encoding reordering, a newly implemented right hemi-diaphragmaitc navigator for respiratory gating was used. Subjective and objective image quality parameters were compared. Respiratory motion artifact suppression has a major impact on image quality in diffusion-weighted imaging of the spine. Phase-encoding reordering does not enhance image quality while right hemi-diaphragmatic respiratory navigator gating significantly improves image quality at the cost of data acquisition time. Navigator gating should be used if standard spin-echo diffusion-weighted imaging demonstrates insufficient image quality.

Importance of the right ventricle in valvular heart disease.

The importance of the right ventricle as a determinant of clinical symptoms, exercise capacity, peri-operative survival and postoperative outcome has been underestimated for a long time. Right ventricular ejection fraction has been used as a measure of right ventricular function but has been found to be dependent on loading conditions, ventricular interaction as well as on myocardial structure. Altered left ventricular function in patients with valvular disease influences right ventricular performance mainly by changes in afterload but also by ventricular interaction. Right ventricular function and regional wall motion can be determined with right ventricular angiography, radionuclide ventriculography, two-dimensional echocardiography or magnetic resonance imaging. However, the complex structure of the right ventricle and its pronounced translational movements render quantification difficult. True regional wall motion analysis is, however, possible with myocardial tagging based on magnetic resonance techniques. With this technique a baso-apical shear motion of the right ventricle was observed which was enhanced in patients with aortic stenosis.

Initial experiences with in vivo right coronary artery human MR vessel wall imaging at 3 tesla.

Due to their relatively small size and central location within the thorax, improvement in signal-to-noise (SNR) is of paramount importance for in vivo coronary vessel wall imaging. Thus, with higher field strengths, coronary vessel wall imaging is likely to benefit from the expected "near linear" proportional gain in SNR. In this study, we demonstrate the feasibility of in vivo human high field (3 T) coronary vessel wall imaging using a free-breathing black blood fast gradient echo technique with respiratory navigator gating and real-time motion correction. With the broader availability of more SNR efficient fast spin echo and spiral techniques, further improvements can be expected.

Multiple plume events in the genesis of the peri-Caribbean Cretaceous oceanic plateau province

The oceanic crust fragments exposed in central America, in north-western South America, and in the Caribbean islands have been considered to represent accreted remnants of the Caribbean-Colombian Oceanic Plateau (CCOP). On the basis of trace element and Nd, Sr, and Pb isotopic compositions we infer that cumulate rocks, basalts, and diabases from coastal Ecuador have a different source than the basalts from the Dominican Republic. The latter suite includes the 86 Ma basalts of the Duarte Complex which are light rare earth element (REE) -enriched and display (relative to normal mid-ocean ridge basalts, NMORB) moderate enrichments in large ion lithophile elements, together with high Nb, Ta, Pb, and low Th contents. Moreover, they exhibit a rather restricted range of Nd and Pb isotopic ratios consistent with their derivation from an ocean island-type mantle source, the composition of which includes the HIMU (high U-238/Pb-204) component characteristic of the Galapagos hotspot. In contrast, the 123 Ma Ecuadorian oceanic rocks have flat REE patterns and (relative to NMORB) are depleted in Zr, Hf, Th, and U. Moreover, they show a wide range of Nd and Pb isotopic ratios intermediate between those of ocean island basalts and NMORB. It is unlikely, on geochemical grounds, that the plume source of the Ecuadorian fragments was similar to that of the Galapagos. In addition, because of the NNE motion of the Farallon plate during the Early Cretaceous, the Ecuadorian oceanic plateau fragments could not have been derived from the Galapagos hotspot but were likely formed at a ridge-centered or near-ridge hotspot somewhere in the SE Pacific.

Relationship between motion of coronary arteries and diaphragm during free breathing: lessons from real-time MR imaging.

OBJECTIVE: Diaphragmatic navigators are frequently used in free-breathing coronary MR angiography, either to gate or prospectively correct slice position or both. For such approaches, a constant relationship between coronary and diaphragmatic displacement throughout the respiratory cycle is assumed. The purpose of this study was to evaluate the relationship between diaphragmatic and coronary artery motion during free breathing. SUBJECTS AND METHODS: A real-time echoplanar MR imaging sequence was used in 12 healthy volunteers to obtain 30 successive images each (one per cardiac cycle) that included the left main coronary artery and the domes of both hemidiaphragms. The coronary artery and diaphragm positions (relative to isocenter) were determined and analyzed for effective diaphragmatic gating windows of 3, 5, and 7 mm (diaphragmatic excursions of 0-3, 0-5, and 0-7 mm from the end-expiratory position, respectively). RESULTS: Although the mean slope correlating the displacement of the right diaphragm and the left main coronary artery was approximately 0.6 for all diaphragmatic gating windows, we also found great variability among individual volunteers. Linear regression slopes varied from 0.17 to 0.93, and r2 values varied from .04 to .87. CONCLUSION: Wide individual variability exists in the relationship between coronary and diaphragmatic respiratory motion during free breathing. Accordingly, coronary MR angiographic approaches that use diaphragmatic navigator position for prospective slice correction may benefit from patient-specific correction factors. Alternatively, coronary MR angiography may benefit from a more direct assessment of the respiratory displacement of the heart and coronary arteries, using left ventricular navigators.

Retrospective feasibility study of simultaneous integrated boost in cervical cancer using Tomotherapy: the impact of organ motion and tumor regression.

BACKGROUND: Whole pelvis intensity modulated radiotherapy (IMRT) is increasingly being used to treat cervical cancer aiming to reduce side effects. Encouraged by this, some groups have proposed the use of simultaneous integrated boost (SIB) to target the tumor, either to get a higher tumoricidal effect or to replace brachytherapy. Nevertheless, physiological organ movement and rapid tumor regression throughout treatment might substantially reduce any benefit of this approach. PURPOSE: To evaluate the clinical target volume - simultaneous integrated boost (CTV-SIB) regression and motion during chemo-radiotherapy (CRT) for cervical cancer, and to monitor treatment progress dosimetrically and volumetrically to ensure treatment goals are met. METHODS AND MATERIALS: Ten patients treated with standard doses of CRT and brachytherapy were retrospectively re-planned using a helical Tomotherapy - SIB technique for the hypothetical scenario of this feasibility study. Target and organs at risk (OAR) were contoured on deformable fused planning-computed tomography and megavoltage computed tomography images. The CTV-SIB volume regression was determined. The center of mass (CM) was used to evaluate the degree of motion. The Dice's similarity coefficient (DSC) was used to assess the spatial overlap of CTV-SIBs between scans. A cumulative dose-volume histogram modeled estimated delivered doses. RESULTS: The CTV-SIB relative reduction was between 31 and 70%. The mean maximum CM change was 12.5, 9, and 3 mm in the superior-inferior, antero-posterior, and right-left dimensions, respectively. The CTV-SIB-DSC approached 1 in the first week of treatment, indicating almost perfect overlap. CTV-SIB-DSC regressed linearly during therapy, and by the end of treatment was 0.5, indicating 50% discordance. Two patients received less than 95% of the prescribed dose. Much higher doses to the OAR were observed. A multiple regression analysis showed a significant interaction between CTV-SIB reduction and OAR dose increase. CONCLUSIONS: The CTV-SIB had important regression and motion during CRT, receiving lower therapeutic doses than expected. The OAR had unpredictable shifts and received higher doses. The use of SIB without frequent adaptation of the treatment plan exposes cervical cancer patients to an unpredictable risk of under-dosing the target and/or overdosing adjacent critical structures. In that scenario, brachytherapy continues to be the gold standard approach.

Atrial arrhythmias in adult patients with right- versus left-sided congenital heart disease anomalies.

Atrial arrhythmias (AAs) are a common complication in adult patients with congenital heart disease. We sought to compare the lifetime prevalence of AAs in patients with right- versus left-sided congenital cardiac lesions and their effect on the prognosis. A congenital heart disease diagnosis was assigned using the International Disease Classification, Ninth Revision, diagnostic codes in the administrative databases of Quebec, from 1983 to 2005. Patients with AAs were those diagnosed with an International Disease Classification, Ninth Revision, code for atrial fibrillation or intra-atrial reentry tachycardia. To ensure that the diagnosis of AA was new, a washout period of 5 years after entry into the database was used, a period during which the patient could not have received an International Disease Classification, Ninth Revision, code for AA. The cumulative lifetime risk of AA was estimated using the Practical Incidence Estimators method. The hazard ratios (HRs) for mortality, morbidity, and cardiac interventions were compared between those with right- and left-sided lesions after adjustment for age, gender, disease severity, and cardiac risk factors. In a population of 71,467 patients, 7,756 adults developed AAs (isolated right-sided, 2,229; isolated left-sided, 1,725). The lifetime risk of developing AAs was significantly greater in patients with right- sided than in patients with left-sided lesions (61.0% vs 55.4%, p <0.001). The HR for mortality and the development of stroke or heart failure was similar in both groups (HR 0.96, 95% confidence interval [CI] 0.86 to 1.09; HR 0.94, 95% CI 0.80 to 1.09; and HR 1.10, 95% CI 0.98 to 1.23, respectively). However, the rates of cardiac catheterization (HR 0.63, 95% CI 0.55 to 0.72), cardiac surgery (HR 0.40, 95% CI 0.36 to 0.45), and arrhythmia surgery (HR 0.77, 95% CI 0.6 to 0.98) were significantly less for patients with right-sided lesions. In conclusion, patients with right-sided lesions had a greater lifetime burden of AAs. However, their morbidity and mortality were no less than those with left-sided lesions, although the rate of intervention was substantially different.

Portal vein embolization before right hepatectomy: prospective clinical trial.

OBJECTIVE: To assess the impact of liver hypertrophy of the future liver remnant volume (FLR) induced by preoperative portal vein embolization (PVE) on the immediate postoperative complications after a standardized major liver resection. SUMMARY BACKGROUND DATA: PVE is usually indicated when FLR is estimated to be too small for major liver resection. However, few data exist regarding the exact quantification of sufficient minimal functional hepatic volume required to avoid postoperative complications in both patients with or without chronic liver disease. METHODS: All consecutive patients in whom an elective right hepatectomy was feasible and who fulfilled the inclusion and exclusion criteria between 1998 and 2000 were assigned to have alternatively either immediate surgery or surgery after PVE. Among 55 patients (25 liver metastases, 2 cholangiocarcinoma, and 28 hepatocellular carcinoma), 28 underwent right hepatectomy after PVE and 27 underwent immediate surgery. Twenty-eight patients had chronic liver disease. FLR and estimated rate of functional future liver remnant (%FFLR) volumes were assessed by computed tomography. RESULTS: The mean increase of FLR and %FFLR 4 to 8 weeks after PVE were respectively 44 +/- 19% and 16 +/- 7% for patients with normal liver and 35 +/- 28% and 9 +/- 3% for those with chronic liver disease. All patients with normal liver and 86% with chronic liver disease experienced hypertrophy after PVE. The postoperative course of patients with normal liver who underwent PVE before right hepatectomy was similar to those with immediate surgery. In contrast, PVE in patients with chronic liver disease significantly decreased the incidence of postoperative complications as well as the intensive care unit stay and total hospital stay after right hepatectomy. CONCLUSIONS: Before elective right hepatectomy, the hypertrophy of FLR induced by PVE had no beneficial effect on the postoperative course in patients with normal liver. In contrast, in patients with chronic liver disease, the hypertrophy of the FLR induced by PVE decreased significantly the rate of postoperative complications.

Octopus Standard Automated Perimetry, Pulsar Perimetry, Moorfields Motion Displacement Test and Heidelberg Retinal Tomography in Glaucoma Detection - A Comparison of Diagnostic Accuracy

Purpose: To investigate the accuracy of 4 clinical instruments in the detection of glaucomatous damage. Methods: 102 eyes of 55 test subjects (Age mean = 66.5yrs, range = [39; 89]) underwent Heidelberg Retinal Tomography (HRTIII), (disc area<2.43); and standard automated perimetry (SAP) using Octopus (Dynamic); Pulsar (TOP); and Moorfields Motion Displacement Test (MDT) (ESTA strategy). Eyes were separated into three groups 1) Healthy (H): IOP<21mmHg and healthy discs (clinical examination), 39 subjects, 78 eyes; 2) Glaucoma suspect (GS): Suspicious discs (clinical examination), 12 subjects, 15 eyes; 3) Glaucoma (G): progressive structural or functional loss, 14 subjects, 20 eyes. Clinical diagnostic precision was examined using the cut-off associated with the p<5% normative limit of MD (Octopus/Pulsar), PTD (MDT) and MRA (HRT) analysis. The sensitivity, specificity and accuracy were calculated for each instrument. Results: See table Conclusions: Despite the advantage of defining glaucoma suspects using clinical optic disc examination, the HRT did not yield significantly higher accuracy than functional measures. HRT, MDT and Octopus SAP yielded higher accuracy than Pulsar perimetry, although results did not reach statistical significance. Further studies are required to investigate the structure-function correlations between these instruments.

The role of the right parietal cortex in sound localization: a chronometric single pulse transcranial magnetic stimulation study.

Auditory spatial functions, including the ability to discriminate between the positions of nearby sound sources, are subserved by a large temporo-parieto-frontal network. With the aim of determining whether and when the parietal contribution is critical for auditory spatial discrimination, we applied single pulse transcranial magnetic stimulation on the right parietal cortex 20, 80, 90 and 150 ms post-stimulus onset while participants completed a two-alternative forced choice auditory spatial discrimination task in the left or right hemispace. Our results reveal that transient TMS disruption of right parietal activity impairs spatial discrimination when applied at 20 ms post-stimulus onset for sounds presented in the left (controlateral) hemispace and at 80 ms for sounds presented in the right hemispace. We interpret our finding in terms of a critical role for controlateral temporo-parietal cortices over initial stages of the building-up of auditory spatial representation and for a right hemispheric specialization in integrating the whole auditory space over subsequent, higher-order processing stages.

Acute aphasia after right hemisphere stroke

Abstract Right hemispheric stroke aphasia (RHSA) rarely occurs in right- or left-handed patients with their language representation in right hemisphere (RH). For right-handers, the term crossed aphasia is used. Single cases, multiple cases reports, and reviews suggest more variable anatomo-clinical correlations. We included retrospectively from our stroke data bank 16 patients (right- and left-handed, and ambidextrous) with aphasia after a single first-ever ischemic RH stroke. A control group was composed of 25 successive patients with left hemispheric stroke and aphasia (LHSA). For each patient, we analyzed four modalities of language (spontaneous fluency, naming, repetition, and comprehension) and recorded eventual impairment: (1) on admission (hyperacute) and (2) between day 3 and 14 (acute). Lesion volume and location as measured on computed tomography (CT) and magnetic resonance imaging (MRI) were transformed into Talairach stereotaxic space. Nonparametric statistics were used to compare impaired/nonimpaired patients. Comprehension and repetition were less frequently impaired after RHSA (respectively, 56% and 50%) than after LHSA (respectively, 84% and 80%, P = 0.05 and 0.04) only at hyperacute phase. Among RHSA, fewer left-handers/ambidextrous than right-handers had comprehension disorders at second evaluation (P = 0.013). Mean infarct size was similar in RHSA and LHSA with less posterior RHSA lesions (caudal to the posterior commissure). Comprehension and repetition impairments were more often associated with anterior lesions in RHSA (Fisher's exact test, P < 0.05). Despite the small size of the cohort, our findings suggest increased atypical anatomo-functional correlations of RH language representation, particularly in non-right-handed patients. Rapport de synthèse : Des aphasies secondaires à un accident vasculaire ischémique cérébral (AVC) hémisphérique droit sont rarement rencontrées chez des patients droitiers ou gauchers avec une représentation du langage dans l'hémisphère droit. Chez les droitiers, on parle d'aphasie croisée. Plusieurs études sur le sujet ont suggéré des corrélations anatomocliniques plus variables. Dans notre étude, nous avons inclus rétrospectivement, à partir d'une base de données de patients avec un AVC, seize patients (droitiers, gauchers et ambidextres) souffrant d'une aphasie suite à un premier et unique AVC ischémique hémisphérique droit. Un groupe contrôle est composé de vingt-cinq patients successifs avec une aphasie suite à un AVC ischémique hémisphérique gauche. Pour chaque patient, nous avons analysé quatre modalités de langage, à savoir la fluence spontanée, la dénomination, la répétition et la compréhension et leur éventuelle atteinte à deux moments distincts : 1) à l'admission (phase hyperaiguë) et 2) entre le 3e et le 14e jour (phase aiguë). Le volume et la localisation de la lésion mesurés, soit sur un CT-scanner soit sur une imagerie par résonance magnétique cérébrale, ont été analysés à l'aide de l'échelle stéréotaxique de Talairach. Des statistiques non paramétriques ont été utilisées pour comparer les patients atteints et non atteints. . La compréhension et la répétition étaient moins souvent atteintes, seulement en phase hyperaiguë, après une aphasie suite à un AVC hémisphérique droit (resp. 56% et 50%) plutôt que gauche (resp. 84 % et 80%, p= 0.05 et 0.04). Parmi les aphasies suite à un AVC ischémique hémisphérique droit, moins de gauchers et d'ambidextres que de droitiers avaient des troubles de la compréhension lors de la seconde évaluation (p=0.013}. La .taille moyenne de la zone infarcie était semblable entre les aphasies droites et gauches, avec moins de lésions postérieures (caudale à la commissure postérieure) lors des aphasies droites. Les troubles de la répétition et de la compréhension étaient plus souvent associés à des lésions antérieures lors d'aphasie droite. (Fischer's exact test, p>0.05). Malgré la petite taille de notre cohorte de patients, ces résultats suggèrent une augmentation des corrélations anatomocliniques atypiques lors d'une représentation du langage dans l'hémisphère droit, surtout chez les patients non droitiers.