[Imaging of the lower limb veins: when and how?]. / Quand et comment réaliser une imagerie des veines des membres?

Evaluation for possible lower limb deep venous thrombosis (DVT) is a very frequently requested examination. In France, imaging diagnosis is essentially based on complete Doppler sonographic evaluation of both lower limbs. In patients with no co-morbid condition, the D-dimer assay is useful to exclude the possibility of DVT. A positive diagnosis of DVT is based on the lack of venous compressibility and abnormal Doppler signal. The diagnostic accuracy relies on adequate knowledge of vascular anatomy and sufficient training, especially at the calf level. For experienced sonographers, the accuracy is similar at the thigh and calf level. In patients with suspected pulmonary embolus, evaluation of the lower extremity veins is mandatory and frequently performed with CT immediately following CT pulmonary angiography. However, this examination has not been validated yet.

Functional MRI of the kidney.

Functional MR imaging of the kidney has a great potential of development because the functional parameters, which can be approached noninvasively, are multiple: glomerular filtration, tubular concentration and transit, blood volume and perfusion, diffusion, and oxygenation. Until now, its limitations in clinical applications are due to the difficulties in obtaining reproducible and reliable information in this mobile organ and, sometimes, in understanding the physiologic substrate of the signal changes observed. These approaches require either endogeneous contrast agents, such as water protons (for perfusion and diffusion) or deoxyhemogobin (for oxgenation), or exogeneous contrast agents such as gadolinium chelates (for filtration and perfusion) or iron oxide particles (for perfusion). Clinical validation of these methods and evaluation of their clinical impact are now worthwhile before diffusing them in clinical practice.

[Non-penetrating vascular staples prevent myo-intimal hyperplasia and maintain arterial vasomotor reaction]. / Les clips de suture vasculaire non pénétrants limitent l'hyperplasie myo-intimale et maintiennent les réactions artérielles.

OBJECTIVES: Vascular anastomosis is still associated with a significant rate of early or delayed complications, particularly restenosis. We have previously demonstrated that non-penetrating clips can help prevent intimal hyperplasia. The aim of this study was to evaluate how well the use of mechanical clips prevents intimal hyperplasia while maintaining arterial vasomotor function. MATERIAL AND METHODS: An aortic suture was performed in 38 rabbits. A standard closure was used for 15 sutures and a small vascular closure staple (VCS) for 23. Morphological analysis was performed with standard staining, histomorphometry and immunochemical staining for smooth muscle and endothelial cells. Vasomotor response was assessed using IntraVacularUltraSound with baseline luminal area and luminal area after injection of acetylcholine and nitroglycerin. Vasomotor response was assessed before suture and before removing the aorta. RESULTS: There was a significant improvement in operating time for closure with vascular staples (8 +/- 2 minutes versus 13 +/- 3 minutes) without thrombosis. We noted reduced intimal hyperplasia with staple closure (0.156 +/- 0.052 versus 0.087 +/- 0.042 mm, p<0.01). There was no difference for the medial thickness and the intima/media ratio was significantly different. The luminal area after suture was significantly better after vascular staple closure (16.78 +/- 0.639 mm(2) versus 17.24 +/- 0.492 mm(2), p=0.016). Vascular response to acteylcholine and nitroglycerin was equivalent for the two groups. CONCLUSION: Vascular closure staples are efficient for arterial closure. These non-penetrating systems prevent intimal hyperplasia and maintain physiological arterial vasomotor response.

[Imaging of adrenal tumors]. / Imagerie des tumeurs de la surrénale.

Adrenal masses may be discovered incidentally by sonography. Nevertheless, CT is the modality of choice for the detection of adrenal mass when primary or secondary neoplasm is suspected. The distinction between benign and metastatic lesions relies mainly on the relatively high lipid content of most of the adenomas. CT (evaluation of non-enhanced attenuation) and MRI (chemical shift imaging) have comparable performances in the evaluation of lipid content. Lipid-poor adenomas benefit from the evaluation of tumoral wash-out, and, if necessary, CT-guided biopsy. Primary neoplasms are uncommon, reliability of biopsy is poor and surgical resection is generally performed.

Interpretation of Doppler signals.

Combining color and spectral data, Doppler signal provides physiologic information about arterial and venous hemodynamics and anatomic information about vessel walls and diameter. Adequate sampling of Doppler signal is required to avoid pitfalls in interpreting spectral changes or color images. The level of information contained in spectral waveforms is high, compared with color display in terms of velocity profile alterations, as in stenoses, and cyclic changes of systolo-diastolic velocities. Therefore, integration of information from both types of Doppler signal representations is mandatory in clinical practice.

Diffusion tensor MRI of the human kidney.

This study characterizes the diffusion anisotropy of the human kidney using a diffusion-weighted, single-shot echo planar imaging (EPI) sequence in order to access the full apparent diffusion tensor (ADT) within one breathhold. The fractional anisotropy (FA) of the cortex and the medulla were found to be 0.22 +/- 0.12 and 0.39 +/- 0.11, respectively (N = 10), which emphasizes the need for rotationally invariant diffusion measurements for clinical applications. Additional limitations for clinical diffusion imaging on the kidney are the strong susceptibility variations within the abdomen that restrict the use of imaging techniques employing long echo trains, and the severe motion sensitivity that limits the available imaging time to one breath-hold. To overcome these problems an isotropic, diffusion-weighted, segmented EPI protocol that facilitates the acquisition of high-resolution diffusion-weighted images within a single breath-hold was implemented. Using this method, the apparent diffusion coefficient (ADC) of the cortex and medulla were found to be 2.89 +/- 0.28. 10(-9) m2/s and 2.18 +/- 0.36. 10(-9) m2/s (N = 10).

[Can minimal arterial aggressions using non-penetrating mechanical clip suture prevent myo-intimal hyperplasia? Preliminary results]. / L'agression artérielle minimale lors de suture par clips mécaniques non pénétrants prévient-elle l'hyperplasie myo-intimale? Résultats préliminaires.

SUBJECT: Vascular anastomosis is still associated with a significant rate of early (stenosis, thrombosis) and delayed (intimal hyperplasia) complications. Even though suture closure remains the most widespread standard procedure, many mechanical systems have been developed mostly using non penetrating clips, aiming to make the suture easier, to reduce the operating time and to reduce the scarring process of the arterial wall. We investigated the usefulness of non penetrating titanium Vascular Closure Staple (VCS) developed for peripheral blood vessels anastomosis, in a study on 20 rabbits with the small VCS system. MATERIAL AND METHODS: On 20 rabbits, 9 of the aortic sutures were done with VCS clips and 11 were done by standard closure. RESULTS: We found a significant improvement in the operating time of the closure (9 +/- 2 minutes versus 14 +/- 4 minutes), early and delayed (10 weeks) patency and the respect of the aorta diameter (0.248 +/- 0.01 centimetres versus 0.246 +/- 0.039 centimetres) and loss of surface (40.3 +/- 5.59% versus 45.6 +/- 6.34%). The main improvement is the reduced intimal hyperplasia (0.128 +/- 0.05 millimetres versus 0.198 +/- 0.032 millimetres. P=0.012). CONCLUSION: Arterial closure can be performed more rapidly with VCS clips than with suture closure, and with a marked reduced reaction of intimal hyperplasia. With those elements it is necessary to continue the experimental studies and to evaluate the VCS sutures at mean and long term.

Doppler frequency shift and time-domain velocity enhancement induced by an ultrasonographic contrast agent.

The aim of this study was to evaluate in rabbit aorta the effect of three bolus doses of Levovist on velocity values measured with spectral Doppler sonography and with time-domain correlation method (color velocity imaging). At each step, a mean peak systolic velocity was calculated from five measurements. These measurements were taken before injection, at 20 s after, at every 30 s till the third minute, and at every minute until return to peak systolic velocity at baseline value. Total duration of enhancement was noted after each injection. After each injection, once the systolic velocity values return to baseline values, a 3 min delay was observed before the following intravenous contrast agent injection was done. With Doppler spectral analysis, after the first injection, peak systolic velocity enhancement was 15 +/- 8.4% (5 to 28%), with a 6.4 +/- 4.3 min duration. After the second injection, peak systolic velocity enhancement was 15.8 +/- 8.4% (5 to 28%) with an 8.8 +/- 4 min duration. After the third injection, it was 14 +/- 9.8% (5 to 34%) with a 13.6 +/- 7.6 min duration (P = 0.04). Peak systolic velocity measured with color velocity imaging remained unchanged after every injection. Doppler velocities were increased by a bolus injection of a contrast agent. Amplitude was not cumulative with the number of injections but was cumulative on its duration. Velocity measurement with time-domain correlation was not influenced by repeated injections.

Volume flow measurement in hemodialysis shunts using time-domain correlation.

Volume flow was measured in 58 hemodialysis shunts (32 grafts and 26 radial fistulas) using the color velocity imaging-quantification method. This method is based on time-domain correlation for velocity calculation and integration of time-varying velocity profiles generated by M-mode sampling. Measurements were made in the brachial artery to estimate radial fistula flow or directly in the grafts. Intraoperator reproducibility was 14.9% for fistulas and 11.6% for grafts. Flow rate was significantly lower in abnormal shunts associated with a functional disorder or a morphologic complication (808 ml/min +/- 484) than in shunts associated with no abnormalities (1401 ml/min +/- 562). Receiver operating characteristic curves showed that a flow rate of 900 ml/min for fistulas and 1300 ml/min for grafts provided 81% and 79% sensitivity and 79% and 67% specificity, respectively. A functional disorder or a morphologic complication was associated with all fistulas and grafts in which flow rates were lower than 500 ml/min and 800 ml/min, respectively.