Activation of mirror-neuron system by erotic video clips predicts degree of induced erection: an fMRI study.

Although visually-induced erection is a common occurrence in human male behaviour, the cerebral underpinnings of this response are not well-known. We hypothesized that the magnitude of induced erection would be linearly correlated with the activation of the mirror-neuron system in response to sexually explicit films. When presented with sexual video clips, eight out of ten healthy subjects had an erectile response demonstrated through volumetric penile plethysmography. The level of activation of the left frontal operculum and of the inferior parietal lobules, areas which contain mirror neurons, predicted the magnitude of the erectile response. These results suggest that the response of the mirror-neuron system may not only code for the motor correlates of observed actions, but also for autonomic correlates of these actions.

Perfusion-weighted MR imaging studies in brain hypervascular diseases: comparison of arterial input function extractions for perfusion measurement.

BACKGROUND AND PURPOSE: Brain hypervascular diseases are complex and induce hemodynamic disturbances on brain parenchyma, which are difficult to accurately evaluate by using perfusion-weighted (PWI) MR imaging. Our purpose was to test and to assess the best AIF estimation method among 4 patients with brain hypervascular disease and healthy volunteers. METHODS: Thirty-three patients and 10 healthy volunteers underwent brain perfusion studies by using a 1.5T MR imaging scanner with gadolinium-chelate bolus injection. PWI was performed with the indicator dilution method. AIF estimation methods were performed with local, regional, regional scaled, and global estimated arterial input function (AIF), and PWI measurements (cerebral blood volume [CBV] and cerebral blood flow [CBF]) were performed with regions of interest drawn on the thalami and centrum semiovale in all subjects, remote from the brain hypervascular disease nidus. Abnormal PWI results were assessed by using Z Score, and evaluation of the best AIF estimation method was performed by using a no gold standard evaluation method. RESULTS: From 88% to 97% of patients had overall abnormal perfusion areas of hypo- (decreased CBV and CBF) and/or hyperperfusion (increased CBV and CBF) and/or venous congestion (increased CBV, normal or decreased CBF), depending on the AIF estimation method used for PWI computations. No gold standard evaluation of the 4 AIF estimates found the regional and the regional scaled methods to be the most accurate. CONCLUSION: Brain hypervascular disease induces remote brain perfusion abnormalities that can be better detected by using PWI with regional or regional scaled AIF estimation methods.

Velocity encoding versus acceleration encoding for pressure gradient estimation in MR haemodynamic studies.

Many methods have been proposed to extract pressure gradient maps from magnetic resonance (MR) images. They were based on the resolution of the haemodynamic model of Navier-Stokes and needed the flow acceleration to be known. Most used velocity data acquisition and computed acceleration from temporal and spatial derivatives of the velocity field. However, MR sequences have been developed in order to acquire the acceleration field directly. Here we compared direct MR measurements of acceleration field components with those calculated from MR velocity acquisitions. Two experimental phantoms were used to separately evaluate the inertial and convective components of the acceleration. Mathematical simulation of the convective phantom further explained the origin of the noise generated by the spatial and temporal derivatives of the velocity data, and the misregistration artefacts due to MR sequences. We found that direct measurement of the acceleration field generates less noise and fewer artefacts than calculation from velocity derivatives.

In vivo proton relaxation times analysis of the skin layers by magnetic resonance imaging.

If in vivo magnetic resonance imaging is nowadays a powerful non-invasive method in medical diagnosis, its application in order to study the skin in vivo is not yet in common use because skin imaging requires a high resolution, at least in the direction perpendicular to the skin surface. We have therefore designed a specific imaging module, which, connected to a standard whole-body imager at 1.5 Tesla, allows us to obtain in vivo magnetic resonance images of skin on most parts of the body. With a depth resolution of about 70 microns, we are able to differentiate the skin layers: epidermis, dermis, subcutaneous fat, and even a thickened stratum corneum on palm as well as on heel. This paper reports the T1 and T2 water proton relaxation times of the different skin layers, in vivo, which are magnetic resonance parameters extracted from the images. Results show that skin layers are characterized by shorter T2 relaxation times than other biologic soft tissues. On the contrary, the measured T1 values are in the same range as in other tissues. These short T2 values may be assigned to the fibrous protein content of the skin and particularly of the dermis. This study on normal skin is the precursor of further works such as the influence of aging. As regards skin pathologies, it will be a powerful tool to follow the evolution of skin diseases under treatment.

Characterization of the skin in vivo by high resolution magnetic resonance imaging: water behavior and age-related effects.

The age-related modifications of magnetic resonance imaging parameters in the skin have been studied in vivo. Modification of these parameters should provide important information about alterations in water structure and content in aged skin. Relaxation times, T1 and T2, and relative proton density, which corresponds to the mobile water proton fraction of tissues, have been measured on people under age 40 and over 70 on a sun-protected area. Results have confirmed in vivo skin layer differentiation through relaxation times performed in a previous study. Moreover, relative proton density quantification has shown that epidermal mobile water is at least twice as abundant as dermal mobile water. No significant age-related T1 and T2 modification could be established, basically because of a large dispersion of values. The main result concerns the upper part of dermis (about 200 microns in thickness) which contains significantly more mobile water protons in chronologic aged skin than in young adult skin. This increase has been related both to an increase of total water content in dermis with age and to an apparent decrease of collagen and proteoglycan content. Associated with alterations of their structure, this decrease reduces macromolecular-water interaction sites. This finding has to be compared with ultrasound evaluation of aged skin, which is characterized by modifications of the echogenicity, related to collagen bundles size and density, in the outer part of dermis, too. Both of the imaging techniques tend to consider the outer part of dermis as one of the privileged sites of skin aging.

The lunula: a magnetic resonance imagining approach to the subnail matrix area.

High-resolution sagittal magnetic resonance images depict an oval area in the dermis beneath the nail matrix that gives a particular signal. This study defines the magnetic resonance imaging characteristics of this area and examines its correlation with the lunula. A high-resolution surface gradient coil specially designed for skin imagining was used on a 1.5 T magnetic resonance unit. The subnail matrix (SNM) areas of 12 subjects had a significantly longer T2 relaxation time and a higher enhancement ratio after injection of gadolinium than did the nail bed dermis. The length of the SNM area distal to the free edge of the proximal nail fold was highly correlated with the length of the lunula (R = 0.98) in 30 fingers and 10 toes. The total length of the SNM area was somewhat correlated with the nail thickness (R = 0.86) in 30 fingers. The histology and microvascularization of the subungual tissue in 21 fingers showed that this SNM area had specific features: The area was composed of loose connective tissue without bundles, and the reticular and subdermal vascular networks had large regular meshes in this oval area. The lunula is shown to be linked to a well-defined area in the underlying dermis with a specific histology and microvascularization.

Lymphedematous skin and subcutis: in vivo high resolution magnetic resonance imaging evaluation.

Physico-chemical and morphologic parameters of skin layers and subcutaneous tissue in lymphedematous limb were studied in vivo using magnetic resonance imaging. High resolution images were obtained with a depth resolution of about 70 microm, using a specific surface gradient coil specially designed for skin imaging and connected to a standard whole-body imager at 1.5 T. Twenty-one patients with unilateral lower extremity lymphedema (11 primary and 10 secondary) were examined. Skin thickness, relaxation times, and relative proton density were calculated in lymphedematous limbs and in contralateral extremities. In diseased limbs, the average skin thickness (2.17 mm) was significantly larger (p = 1.5 x 10(-4)) than that of contralateral limb (1.14 mm). Major cutaneous alterations due to lymphedema took place in dermis. In lymphedematous dermis, the significant increase of relaxation time values could be due to a shift in the equilibrium of water inside this tissue in relation to the interactions between macromolecules and water molecules. In lymphedematous epidermis our results showed an increase in the number of free water protons. Information about water and fat distribution in lymphedema was also obtained using chemical shift weighted images. Our results demonstrated a water retention diffusely spread over the entire dermis, and an important fluid retention located in the interlobular spacing and beside the superficial fascia. Inside the subcutis, the mean thickness of the superficial fat lobules was increased more than that of the deep fat lobules. From all the various measurements we could not distinguish primary from secondary lymphedema.

Radiologic assessment of intranodal vascularity in head and neck squamous cell carcinoma. Correlation with histologic vascular density.

RATIONALE AND OBJECTIVES: Nodal response to chemotherapy in head and neck squamous cell carcinoma depends on the vascularization. The authors assessed different techniques in detecting nodal vascularization. METHODS: Fourteen patients with head and neck tumor were included before surgical treatment. The largest metastatic lymph node (mean axial scanographic diameters 30 x 20 mm) was studied by color and pulsed Doppler, and dynamic magnetic resonance images, processed by factor analysis of medical image sequences (FAMIS), which estimates physiologic contrast enhancement kinetics (factors) and their spatial distributions (factor images). Results were compared with the histologic microvessel density (MVD). Using light microscopy, MVD was estimated by the vascular surface (by staining endothelial cells) to the stroma surface ratio x 100. RESULTS: Three factors were identified by FAMIS: a constant factor in necrosis, an earlier F1 factor and a later F2 factor in normal lymphoid areas and neoplastic stroma. Color flow signal was detected when the MVD was greater than 6.36. CONCLUSIONS: Only one model of vascularization was extracted by FAMIS, with no difference between neoplastic and spared lymphoid areas. The presence of color-flow signals could help predict the response of metastatic lymph nodes to chemotherapy.

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

UNLABELLED: 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 cerebrospinal 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.

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.

CSF flow measurement in syringomyelia.

BACKGROUND AND PURPOSE: CSF circulation has been reported to represent a major factor in the pathophysiology of syringomyelia. Our purpose was to determine the CSF flow patterns in spinal cord cysts and in the subararachnoid space in patients with syringomyelia associated with Chiari I malformation and to evaluate the modifications of the flow resulting from surgery. METHODS: Eighteen patients with syringomyelia were examined with a 3D Fourier encoding velocity imaging technique. A prospectively gated 2D axial sequence with velocity encoding in the craniocaudal direction in the cervical region was set at a velocity of +/- 10 cm/s. Velocity measurements were performed in the larger portion of the cysts and, at the same cervical level, in the pericystic subarachnoid spaces. All patients underwent a surgical procedure involving dural opening followed by duroplasty. Pre- and postoperative velocity measurements of all patients were taken, with a mean follow-up of 10.2 months. We compared the velocity measurements with the morphology of the cysts and with the clinical data. Spinal subarachnoid spaces of 19 healthy subjects were also studied using the same technique. RESULTS: A pulsatile flow was observed in syrinx cavities and in the pericystic subarachnoid spaces (PCSS). Preoperative maximum systolic cyst velocities were higher than were diastolic velocities. A systolic velocity peak was well defined in all cases, first in the cyst and then in the PCSS. Higher systolic and diastolic cyst velocities are observed in large cysts and in patients with a poor clinical status. After surgery, a decrease in cyst volume (evaluated on the basis of the extension of the cyst and the compression of the PCSS) was observed in 13 patients. In the postoperative course, we noticed a decrease of systolic and diastolic cyst velocities and a parallel increase of systolic PCSS velocities. Diastolic cyst velocities correlated with the preoperative clinical status of the patients and, after surgery, in patients with a satisfactory foraminal enlargement evaluated on the basis of the visibility of the cisterna magna. CONCLUSION: CSF flow measurement constitutes a direct evaluation for the follow-up of patients with syringomyelic cysts. Diastolic and systolic cyst velocities can assist in the evaluation of the efficacy of surgery.

A computer algorithm for the simulation of any nuclear magnetic resonance (NMR) imaging method.

More than a dozen Nuclear Magnetic Resonance (NMR) imaging methods have been described using different radio-frequency pulse sequences, magnetic field gradient variations, and data processing. In order to have a theoretical understanding in the most general case, we have conceived a computer program for the simulation of NMR imaging techniques. The algorithm uses the solution of the Bloch equations at each point of a simulated object. The direction of every elementary magnetic moment is computed at each instant, and stored in an array giving the global signal to be processed, whatever the pulse and gradient sequence. To test the validity of this program, we have simulated some well-known experimental results. Some applications are presented which contribute to the understanding of image distortions and to techniques such as selective radio-frequency pulse or oscillating gradients. This program can be used to unravel physical and technological causes of image distortions, to have a "microscopic" look at any parameter of an experiment, and to study the contrast given by various NMR imaging techniques as a function of the three NMR parameters, i.e., the hydrogen nuclei density rho and the relaxation times T1 and T2.

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.

Implementation and optimization by the simplex method of a 3D double echo sequence in steady-state free precession.

Under steady-state conditions, the resulting echoes have very complex T1 and T2 relationships. Many authors exploited these echoes in different sequences to produce either T1- or T2-weighted images. The simultaneous acquisition of two echoes in a single sequence provides two images of clearly different contrasts. We implemented such a sequence, in a 3D-acquisition mode, combining the advantages of thin and contiguous slices with those of a multi-echo sequence. The contrast of the images was correlated with theoretical results, derived from Bloch equations. In order to estimate the acquisition parameters (alpha, TE, TR) to obtain an optimal T1- or T2-contrast between two tissues, a computer simulation of these equations was used in conjunction with the simplex method. The results show that this sequence improves the clinical efficiency of MRI, particularly in neurological and articular disease.

Origin of subarachnoid cerebrospinal fluid pulsations: a phase-contrast MR analysis.

Cerebrospinal fluid (CSF) pulsations result from change of blood volume in the closed craniospinal cavity. We used cine phase contrast MR analysis to determine whether spinal CSF pulsations result from spinal vascular pulsations or intracranial subarachnoid pulsations, whether intracranial CSF pulsations result from intracranial large arteries pulsations or cerebrovascular bed changes. We performed a quantified physiological mapping of CSF velocity waveforms along the craniospinal axis. Thirty-six volunteers participated in the study. MR acquisitions were obtained at the intracranial level, the upper, midcervical, cervicothoracic, mid thoracic, and/or the thoracolumbar levels. The temporal velocity information were plotted as wave form and key temporal parameters were determined and analyzed; intervals from the R wave to the onset of CSF systole, to CSF systolic peak, to the end of systole, as well as duration of systole. Three kinds of dynamic channels could be differentiated along the spinal axis, the lateral, medioventral and mediodorsal channels. Lateral spinal CSF pulse waves show significant craniocaudal propagation. No such significant progression was detected through the medial channels along the spine. Through the medial channels, a cephalic progression was observed from the upper cervical level to the intracranial level. At the craniocervical junction, mediodorsal CSF systole appeared the earliest one whereas in the anterior intracranial basal cistern, CSF systole appeared delayed. In conclusion, spinal CSF pulsations seem to result mainly from intracranial pulsations in the lateral channels, whereas local vascular pulsations could modify CSF pulse wave mainly in the medial channels. At the craniocervical junction, our results suggest that blood volume change in the richly vascularised cerebellar tonsils is the main initiating factor of CSF systole; and that spinal vascular pulsations could be considered as an additional early and variable CSF pump.

Spectroscopic MRI: a tool for the evaluation of systemic lipid storage disease.

Spectroscopic MR imaging allows to measure the lipid content of a region inside the human body. This technique has been applied to the case of a woman with a severe multisystemic triglyceride storage disease. Lipid contents of liver, pancreas, kidneys, left ventricle, skeletal muscles (calves, thighs, arms) were measured by using the Dixon spectroscopic imaging sequence. In some heterogeneous muscles, localized proton spectra were recorded. Results agreed with clinical findings (muscle weakness, normal renal and cardiac function, diabetes). These techniques could help to quantify the severity of the disease and to follow up its evolution under therapy.

High resolution T1 weighted magnetic resonance imaging of the deep brain structures using a reduced bandwidth.

High spatial resolution T1 weighted images of the brain were acquired in 5-13 min on a whole-body magnetic resonance imager operating at 1.5 T. In order to obtain 5-8 cm field of view images, the receiver bandwidth (Bw) was lowered to 2 kHz. The use of a 2 kHz Bw, instead of the standard 16 kHz Bw, partially compensated the signal loss due to the small pixel size by increasing the signal-to-noise ratio, without scan time penalty. The chemical shift artifact associated with reduced Bw was not observed because fat signal is negligible in the brain.

Evaluation of error bounds on calcaneal speed of sound caused by surrounding soft tissue.

For absorptiometry measurements, soft tissue may have an impact on quantitative ultrasound (QUS) measurements. In the present study, we focused primarily on the quantification of measurement error on speed of sound (SOS) caused by surrounding soft tissue. The relevant soft tissue parameters affecting the inherent SOS inaccuracies are thickness and sound velocity. To meet our goal, SOS measurements were taken at the right heel using a QUS imaging device in 21 healthy subjects. Site-matched measurements of soft tissue thickness (STT) and bone width were performed using magnetic resonance imaging of the heel. Several bone velocities were calculated either by accounting for bone width (SOSBW) only or by taking into account the exact path lengths of all major components traversed by ultrasound &lapr;V(b)). Given that soft tissue composition is difficult to determine in vivo, we chose to estimate lower and upper error bounds on bone velocity (V(b lower) and V(b upper)) by spanning the full range of available values in the literature. The mean BW was 30.7 +/- 2.7 mm and the mean medial and external STTs were 8.8 +/- 1.7 and 8.5 +/- 1.5 mm, respectively. Accounting for true BW only resulted in no significant difference between SOS (1533 +/- 37) and SOSBW (1531 +/- 33). By contrast, accounting for both true BW and surrounding soft tissue resulted in an increase in the calculated bone velocity and statistically significant differences between SOS and V(b upper) (1568 +/- 36) and V(b lower) (1542 +/- 34). Root mean square errors between SOS and the calculated velocities were 0.34, 2. 32, and 0.70% for SOSBW, V(b upper), and V(b lower), respectively. We report here measurement errors caused by soft tissue to be 3 to 20 times higher than the SOS short-term precision (SOS coefficient of variation of 0.1%). Our results suggest that inaccuracies in SOS measurement caused by overlying soft tissue cannot be neglected. Overlying soft tissues may influence outcomes of longitudinal studies, especially if variations in tissue thickness and composition occur during the longitudinal follow-up. A practical way of minimizing the measurement error could be to perform an adequate correction for the overlying soft tissue. However, ideally, this should require knowing both the thickness and sound velocity in soft tissue. One might preferably conduct experimental investigations that directly control soft tissue thickness and composition to resolve this problem.

[Mass and geometry of the left ventricle. Contribution of ultrafast computed x-ray tomography and magnetic resonance imaging]. / Masse et géométrie ventriculaire gauche. Apports de la tomodensitométrie ultrarapide et de l'imagerie par résonance magnétique.

Ultrafast computed tomography and magnetic resonance imaging are two new methods of cardiac imaging. Measurements of left ventricular volume (end-diastolic, end-systolic volume, stroke volume) and mass have been validated with both methods. The calculations are independent of the geometric shape of the ventricle. Although regional analysis is difficult because of the complex movement of the left ventricle in the tomographic cuts, these methods present a number of advantages: excellent temporospatial tomographic resolution, approximately the same in all dimensions, appreciation of endocardial movement from an epicardial centre, the potential to record their transform spatial data in 3 dimensions from initial planar acquisition. However, all potential regional measurements are still being validated as they are operator-dependent and require visual identification and manual tracing of the cardiac contours or local infrastructures which affect the results of these techniques which are still relatively little used in cardiac imaging. In the context of clinical evaluation, these relatively non-invasive methods will become extremely accurate in the appreciation of parameters of left ventricular geometry and function. They will become very useful in the determination of the myocardial effects of drugs, surgery or other interventional procedures in different models of cardiac disease.

[Diffusion, perfusion and activation functional MRI studies of brain arteriovenous malformations]. / Explorations des malformations artérioveineuses cérébrales en IRM fonctionnelle de diffusion, de perfusion er d'ativation.

The management of Brain Arteriovenous Malformations continues to be challenged by a lack of understanding and control of pathophysiological processes implied in the clinical symptoms. New data from functional MRI with diffusion-weighted, perfusion-weighted and neuronal activation highlight abnormal brain areas near or remote to the AVM nidus. Moreover, these techniques are able to show hemodynamic and neuronal adaptative phenomena involved in brain plasticity. They reflect the instantaneous hemodynamic brain conditions that may help to correlate the clinical symptoms with the anatomical and functional substratum and to influence any invasive therapy.