Jacques Bittoun

Brain processing of visual sexual stimuli in healthy men: a functional magnetic resonance imaging study.

The brain plays a central role in sexual motivation. To identify cerebral areas whose activation was correlated with sexual desire, eight healthy male volunteers were studied with functional magnetic resonance imaging (fMRI). Visual stimuli were sexually stimulating photographs (S condition) and emotionally neutral photographs (N condition). Subjective responses pertaining to sexual desire were recorded after each condition. To image the entire brain, separate runs focused on the upper and the lower parts of the brain. Statistical Parametric Mapping was used for data analysis. Subjective ratings confirmed that sexual pictures effectively induced sexual arousal. In the S condition compared to the N condition, a group analysis conducted on the upper part of the brain demonstrated an increased signal in the parietal lobes (superior parietal lobules, left intraparietal sulcus, left inferior parietal lobule, and right postcentral gyrus), the right parietooccipital sulcus, the left superior occipital gyrus, and the precentral gyri. In addition, a decreased signal was recorded in the right posterior cingulate gyrus and the left precuneus. In individual analyses conducted on the lower part of the brain, an increased signal was found in the right and/or left middle occipital gyrus in seven subjects, and in the right and/or left fusiform gyrus in six subjects. In conclusion, fMRI allows to identify brain responses to visual sexual stimuli. Among activated regions in the S condition, parietal areas are known to be involved in attentional processes directed toward motivationally relevant stimuli, while frontal premotor areas have been implicated in motor preparation and motor imagery. Further work is needed to identify those specific features of the neural responses that distinguish sexual desire from other emotional and motivational states.

CPMG measurements and ultrafast imaging in human lungs with hyperpolarized helium-3 at low field (0.1 T)

This work reports the use of single‐shot spin echo sequences to achieve in vivo diffusion gas measurements and ultrafast imaging of human lungs, in vivo, with hyperpolarized 3He at 0.1 T. The observed transverse relaxation time of 3He lasted up to 10 s, which made it possible to use long Carr‐Purcell‐Meiboom‐Gill echo trains. Preliminary NMR studies showed that the resolution of lung images acquired with hyperpolarized 3He and single‐shot sequences is limited to about 6 mm because of the diffusion of the gas in applied field gradients. Ultrafast images of human lungs in normal subjects, achieved in less than 0.4 s with the equivalent of only 130 μmol of fully polarized 3He, are presented. Comparison with other studies shows that there is no SNR penalty by using low fields in the hyperpolarized case. Advantage was taken of the self diffusion‐weighting of the rapid acquisition with relaxation enhancement (RARE) sequence to acquire apparent diffusion coefficient (ADC) images of the lungs. Time scales of seconds could be explored for the first time because there is no hindrance from T  *2 as with the usual approaches. At 0.1 T, 180° RF pulses can be repeated every 10 ms without exceeding specific absorption rate limits, which would not be the case for higher fields. Moreover, at low field, susceptibility‐induced phenomena are expected to be milder. This supports the idea that low‐field imagers can be used for hyperpolarized noble gas MRI of lungs and may be preferred for ADC measurements. Magn Reson Med 47:75–81, 2002.

Standard and high resolution magnetic resonance imaging of glomus tumors of toes and fingertips

BACKGROUND High-resolution magnetic resonance imaging (MRI) of subungual glomus tumors has been recently reported. OBJECTIVE Our purpose was to compare high-resolution MRI and standard MRI for the diagnosis of 44 glomus tumors of the toes and fingertips. METHODS Glomus tumors (11 cases) were first examined by MRI with a commercial surface coil (set 1). Thirty-three other glomus tumors and one tumor from set 1 were then examined with a high-resolution module designed for skin imaging (set 2). RESULTS All 44 glomus tumors were identified with MRI. The limits of the tumors were detected in 54% of set 1 and 100% of set 2. A capsule was present in most cases, but was incomplete or absent in eight cases. Subtypes of glomus tumors were more easily differentiated in set 2. CONCLUSION Standard MRI was adequate to detect glomus tumors, but high-resolution MRI assessed tumor characteristics more accurately.

Relation between Cerebral Blood Flow and Metabolism Explained by a Model of Oxygen Exchange

The cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) are major determinants of the contrast in functional magnetic resonance imaging and optical imaging. However, the coupling between CBF and CMRO2 during cerebral activation remains controversial. Whereas most of the previous models tend to show a nonlinear coupling, experimental studies have led to conflicting conclusions. A physiologic model was developed of oxygen transport through the blood–brain barrier (BBB) for dynamic and stationary states. Common model simplifications are proposed and their implications for the CBF/CMRO2 relation are studied. The tissue oxygen pool, the BBB permeability, and the hemoglobin dissociation curve are physiologic parameters directly involved in the CBF/CMRO2 relation. We have been shown that the hypothesis of a negligible tissue oxygen pool, which was admitted by most of the previous models, implies a tight coupling between CBF and CMRO2. By relaxing this hypothesis, a real uncoupling was allowed that gives a more coherent view of the CBF/CMRO2 relation, in better agreement with the hypercapnia data and with the variability reported in experimental works for the relative changes of those two variables. This also allows a temporal mismatch between CBF and CMRO2, which influences the temporal shape of oxygenation at the capillary end.

Cerebrospinal fluid flow waveforms: MR analysis in chronic adult hydrocephalus.

Henry-Feugeas MC, Idy-Peretti I, Baledent O, et al. Cerebrospinal fluid flow waveforms: MR analysis in chronic adult hydrocephalus. Invest Radiol 2001;36:146–154. rationale and objectives. To analyze changes in cere-brospinal fluid (CSF) hydrodynamics in chronic adult hydrocephalus. methods.Phase-contrast cine-MR acquisitions were used to explore the ventricular system and the upper ventral cervical spaces of 16 patients. The aqueductal jet was explored in 32 control subjects. results.The duration of pulsatile caudal CSF flow (ie, CSF systole) was abnormally short in patients with active idiopathic and obstructive hydrocephalus. The duration of CSF cervical systole was normal in patients with stable hydrocephalus. The aqueductal stroke volume could be increased in stable communicating hydrocephalus. Patients who responded to shunting had shortened CSF systoles and hyperpulsatile ventricular patterns. Successful CSF diversion resulted in longer CSF systoles and CSF ventricular patterns that were no longer hyperpulsatile. conclusions.Magnetic resonance analysis of CSF flow can show craniospinal dissociation and limitation of CSF outflow from the ventricles in both obstructive and communicating hydrocephalus; it should help determine the response to shunting in communicating hydrocephalus.

Phase-contrast velocimetry with hyperpolarized 3He for in vitro and in vivo characterization of airflow

This paper describes a technique that combines radial MRI and phase contrast (PC) to map the velocities of hyperpolarized gases (3He) in respiratory airways. The method was evaluated on well known geometries (straight and U‐shaped pipes) before it was applied in vivo. Dynamic 2D maps of the three velocity components were obtained from a 10‐mm slice with an in‐plane spatial resolution of 1.6 mm within 1 s. Integration of the in vitro through‐plane velocity over the slice matched the input flow within a relative precision of 6.4%. As expected for the given Reynolds number, a parabolic velocity profile was obtained in the straight pipe. In the U‐shaped pipe the three velocity components were measured and compared to a fluid‐dynamics simulation so the precision was evaluated as fine as 0.025 m s−1. The technique also demonstrated its ability to visualize vortices and localize characteristic points, such as the maximum velocity and vortex‐center positions. Finally, in vivo feasibility was demonstrated in the human trachea during inhalation. Magn Reson Med, 2006.

Multidimensional MR mapping of multiple components of velocity and acceleration by fourier phase encoding with a small number of encoding steps

Previous studies have shown that the multi‐step approach of velocity or acceleration encoding is highly efficient in terms of the signal‐to‐noise ratio per unit time. This work describes a multidimensional extension of this method for simultaneously measuring multiple components of velocity and acceleration with a few encoding steps. N flow dimensions were encoded with an ND‐matrix, obtained by combining the various flow‐encoding gradients. The small matrix obtained with as few as two encoding steps can be extended by zero‐filling in all N dimensions and using ND‐Fourier transformation to obtain the maximum of the resulting peak in the ND‐matrix, which gives simultaneously all the components of velocity and/or acceleration. The processing time was shortened by using a method of phase computation that gives the same precision as Fourier transformation, but is much faster. A rotating disk was used to show that the velocity‐to‐noise ratio increases with the number of dimensions acquired, demonstrating the efficiency of multidimensional flow measurements. The feasibility of the method is illustrated by 3D maps of the myocardium velocity, and 2D measurement of velocity and acceleration in the ascending aorta—both obtained by multidimensional phase encoding in volunteers. Magn Reson Med 44:723–730, 2000.

Precision of magnetic resonance velocity and acceleration measurements: Theoretical issues and phantom experiments

Magnetic resonance (MR) sequences have been developed for acquiring multiple components of velocity and/or acceleration in a reasonable time and with a single acquisition. They have many parameters that influence the precision of measurements: NS, the number of flow‐encoding steps; NEX, the number of signal accumulations; and ND, the number of dimensions. Our aims were to establish a general relationship revealing the precision of these measurements as a function of NS, ND, and NEX and to validate it by experiments using phantoms. Previous work on precision has been restricted to two‐step (NS = 2) or 1D (ND = 1) MR velocity measurements. We describe a comprehensive approach that encompasses both multistep and multidimensional strategies. Our theoretical formula gives the precision of velocity and acceleration measurements. It was validated experimentally with measurements on a rotating disk phantom. This phantom was much easier to handle than fluid‐based phantoms. It could be used to assess both velocity and acceleration sequences and provided accurate and precise assessments over a wide, adjustable range of values within a single experiment. Increasing each of the three parameters, NS, ND, and NEX, improves the precision but makes the acquisition time longer. However, if only one parameter is to be assessed, maximizing the number of steps (NS) is the most efficient way of improving the precision of measurements; if several parameters are of interest, they should be measured simultaneously. By contrast, increasing the number of signals accumulated (NEX) is the least efficient strategy. J. Magn. Reson. Imaging 2001;13:445–451.

MR imaging of hemophilic arthropathy of the knee: Classification and evolution of the subchondral cysts

Magnetic resonance imaging was performed to assess the subchondral bone of the knee in 64 patients with severe hemophilia A. Using this method, subchondral cysts could be detected and evaluated. We separated the cysts into four classes (LL, LH, HH, C) depending on their signal intensities on T1- and T2-weighted images. Follow-up studies, performed on 25 patients during a period of 10-30 mo after the initial examination, suggest that these four classes of cysts correspond to four successive stages. Morphological changes within a class of cysts were also observed. Although histological confirmation was not possible, this study demonstrated that magnetic resonance imaging allows a better understanding of the pathophysiology and the natural evolution of the subchondral cysts in hemophilic arthropathy.

Functional MR imaging of the human sensorimotor cortex during haptic discrimination.

THIS study attempted to determine whether haptic discriminations of shape (haptic task) activate the same tissue in the central cortical region of normal human subjects as do finger movements (opposition task). Opposition and haptic tasks both activated the central sulcus, as expected from previous imaging studies. The haptic task activated about 50% of the cortical territory activated by the opposition task. The results suggest that exploratory digital movements performed to collect precise somatosensory information and automatic movements performed during finger positioning activate partially overlapping parts of the sensorimotor cortex.