Cue-invariant activation in object-related areas of the human occipital lobe.

The extent to which primary visual cues such as motion or luminance are segregated in different cortical areas is a subject of controversy. To address this issue, we examined cortical activation in the human occipital lobe using functional magnetic resonance imaging (fMRI) while subjects performed a fixed visual task, object recognition, using three different primary visual cues: motion, texture, or luminance contrast. In the first experiment, a region located on the lateral aspect of the occipital lobe (LO complex) was preferentially activated in all 11 subjects both by luminance and motion-defined object silhouettes compared to full-field moving and stationary noise (ratios, 2.00+/-0.19 and 1.86+/-0.65, respectively). In the second experiment, all subjects showed enhanced activation in the LO complex to objects defined both by luminance and texture contrast compared to full-field texture patterns (ratios, 1.43+/-0.08 and 1.32+/-0.08, respectively). An additional smaller dorsal focus that exhibited convergence of object-related cues appeared to correspond to area V3a or a region slightly anterior to it. These results show convergence of visual cues in LO and provide strong evidence for its role in object processing.

Differential processing of objects under various viewing conditions in the human lateral occipital complex.

The invariant properties of human cortical neurons cannot be studied directly by fMRI due to its limited spatial resolution. Here, we circumvented this limitation by using fMR adaptation, namely, reduction of the fMR signal due to repeated presentation of identical images. Object-selective regions (lateral occipital complex [LOC]) showed a monotonic signal decrease as repetition frequency increased. The invariant properties of fMR adaptation were studied by presenting the same object in different viewing conditions. LOC exhibited stronger fMR adaptation to changes in size and position (more invariance) compared to illumination and viewpoint. The effect revealed two putative subdivisions within LOC: caudal-dorsal (LO), which exhibited substantial recovery from adaptation under all transformations, and posterior fusiform (PF/LOa), which displayed stronger adaptation. This study demonstrates the utility of fMR adaptation for revealing functional characteristics of neurons in fMRI studies.

Internal mechanical conditions in the soft tissues of a residual limb of a trans-tibial amputee.

Most trans-tibial amputation (TTA) patients use a prosthesis to retain upright mobility capabilities. Unfortunately, interaction between the residual limb and the prosthetic socket causes elevated internal strains and stresses in the muscle and fat tissues in the residual limb, which may lead to deep tissue injury (DTI) and other complications. Presently, there is paucity of information on the mechanical conditions in the TTA residual limb during load-bearing. Accordingly, our aim was to characterize the mechanical conditions in the muscle flap of the residual limb of a TTA patient after donning the prosthetic socket and during load-bearing. Knowledge of internal mechanical conditions in the muscle flap can be used to identify the risk for DTI and improve the fitting of the prosthesis. We used a patient-specific modelling approach which involved an MRI scan, interface pressure measurements between the residual limb and the socket of the prosthesis and three-dimensional non-linear large-deformation finite-element (FE) modelling to quantify internal soft tissue strains and stresses in a female TTA patient during static load-bearing. Movement of the truncated tibia and fibula during load-bearing was measured by means of MRI and used as displacement boundary conditions for the FE model. Subsequently, we calculated the internal strains, strain energy density (SED) and stresses in the muscle flap under the truncated bones. Internal strains under the tibia peaked at 85%, 129% and 106% for compression, tension and shear strains, respectively. Internal strains under the fibula peaked at substantially lower values, that is, 19%, 22% and 19% for compression, tension and shear strains, respectively. Strain energy density peaked at the tibial end (104kJ/m(3)). The von Mises stresses peaked at 215kPa around the distal end of the tibia. Stresses under the fibula were at least one order of magnitude lower than the stresses under the tibia. We surmise that our present patient-specific modelling method is an important tool in understanding the etiology of DTI in the residual limbs of TTA patients.

In vivo molecular imaging of met tyrosine kinase growth factor receptor activity in normal organs and breast tumors.

Molecular imaging techniques allow visualization of specific gene products and their physiological processes in living tissues. In this study, we present a new approach for molecular imaging of endogenous tyrosine kinase receptor activity. Met and its ligand hepatocyte growth factor scatter factor (HGF/SF), which mediate mitogenicity, tumorigenicity, and angiogenesis, were used as a model. HGF/SF and Met play a significant role in the pathogenesis and biology of a wide variety of human epithelial cancers and, therefore, may serve as potential targets for cancer prognosis and therapy. We have shown previously that in vitro activation of Met by HGF/SF increases oxygen consumption. In this study, we demonstrate that Met activation in vivo by HGF/SF alters the hemodynamics of normal and malignant Met-expressing tissues. Tumor-bearing BALB/C mice were i.v. injected with HGF/SF and imaged using magnetic resonance imaging (MRI) and Doppler ultrasound. Organs and tumors expressing high levels of Met showed the most substantial alteration in blood oxygenation levels as measured by blood oxygenation level depended (BOLD)-MRI. No significant alteration was observed in tumors or organs that does not express Met. In the liver, which expresses high levels of Met, MRI signal alteration of about 60% was observed. In the kidneys, signal alteration was approximately 30%, and no change was observed in muscles. The extent of MRI signal alteration was also in correlation with HGF/SF doses. Injection of 7 and 170 ng/g body weight resulted in signal alteration of 5% and 30%, respectively, in tumors. Doppler ultrasound measurements demonstrated that these MRI changes are at least partially attributable to altered blood flow. These hemodynamic alterations, measured by MRI and Doppler ultrasound, were used in this study for the molecular imaging of Met activity in vivo. This novel molecular imaging technique may be used for in vivo diagnosis, prognosis, and therapy of Met-expressing tumors.

Risk factors associated with postpartum ovarian vein thrombosis.

Thrombosis of the ovarian vein is a remarkable process occuring within a few days of labor in 1:500-1:2000 women. Its presentation is characterized by fever, abdominal pain and occasionally by a palpable abdominal mass that in earlier years sometimes lead to explorative laparotomy. With the advent of modern imaging techniques the diagnosis can be made relatively easily. The pathogenesis has been attributed to an infectious process expanding from the uterus to the right ovarian vein and stasis. A predisposition towards thrombosis has not been so far explored. In this study we retrospectively analysed the clinical features, diagnosis and treatment of 22 patients with objective documentation of post partum ovarian vein thrombosis (POVT) and assessed potential risk factors. In 11 of the 22 patients (50%) inherited prothrombotic risk factors were detected as follows: 4 were heterozygous for factor V G1691A, 2 had protein S deficiency, one had protein S deficiency and was heterozygous for factor V G1691A, and 4 were homozygous for MTHFR C677T. Eight of the 11 patients who bore a prothrombotic predisposition underwent cesarean section. Taken together, the data suggest that POVT may result from the combined effect of an infection, cesarean section and a prothrombotic tendency.

Coronary calcium as a reliable tool for differentiating ischemic from nonischemic cardiomyopathy.

In conclusion, the presence or absence of coronary calcium as detected by this rapid technique represents a simple and reliable noninvasive sign for the differential diagnosis between ischemic and nonischemic DC.

Usefulness of spiral computed tomography (dual-slice mode) for the detection of coronary artery calcium in patients with chronic atypical chest pain, in typical angina pectoris, and in asymptomatic subjects with prominent atherosclerotic risk factors.

The prevalence and extent of coronary calcium were retrospectively assessed by spiral computed tomography in 541 patients (mean age 62 +/- 9 years), of whom 101 had typical angina pectoris, 307 had atypical chest pain, and 133 were asymptomatic subjects with prominent atherosclerotic risk factors. The highest prevalence of coronary calcium was in men with angina pectoris (89%), whereas it was not detected in 48% of men and 56% of women with atypical chest pain.

Blood flow measurements in the iliac arteries by an improved angiographic cinedensitometric technique.

The blood flow of iliac arteries was measrued by means of an improved angiographic chindensitometric technique. This consists of cineradiographic recording of contrast injection into the iliac arteries, followed by optical analysis of the "washout" phase of the contrast material at selected sites. In 25 pateints without perpheral vascular disease, undergoing abdominal angiography for different reasons, the blood flow measruements in left iliac arteries were within the limits of 371-766 ml

Splenic vein thrombosis in patients with a normal size spleen.

The frequency of splenic vein obstruction secondary to pancreatic or retroperitoneal diseases has been only recently appreciated. The diagnosis is important because it frequently results in development of gastric and duodenal varices. It is often assumed that the diagnosis should only be suspected in patients with splenomegaly. This report describes 19 patients in whom splenic vein thrombosis was diagnosed by angiography although clinically unsuspected. In 11, the spleen was normal in size although extensive gastric varices were present. In 3 patients the presenting problem was massive hematemesis. Review of the upper gastrointestinal examinations in these patients showed thickened gastric or duodenal folds although in the absence of esophageal varices, the diagnosis was not made prior to angiography. More liberal use of angiography in patients with an appropriate clinical background, such as a history of pancreatitis, may lead to earlier and more frequent diagnosis of splenic vein obstruction. Varices that result from splenic vein obstruction can be cured by splenectomy.

Relationship of pressure and flow to arterial diameter.

The effects of manipulations of blood pressure and flow on the diameter of the femoral artery in dogs were studied. Diameter measurements were made utilizing real time ultrasound scanning. Although diameter of a flexible tube in a mechanical system varies with internal pressure, in the intact femoral artery the diameter varied with changes in blood flow rate rather than pressure. Increase in blood flow rate resulted in increase in vessel diameter, whether the pressure changed or remained the same. Decrease in blood flow rate resulted in decrease in diameter, irrespective of the pressure. However, when a segment of the femoral artery was isolated from the femoral artery by interposition between plastic tubes, the diameter of the isolated segment no longer increased when flow increased. These findings suggest that arterial diameter is regulated by a conducting mechanism that depends on vascular continuity.

Ultrasonic attenuation maps of liver based on a conventional B-scan and an amplitude loss technique.

The authors present a novel ultrasonic amplitude loss technique, using image processing techniques and designed for computation of local attenuation estimates. Three different estimation approaches were evaluated: the extended Prony, the maximum likelihood, and the least squares approaches. The latter two approaches were found to result in a much higher estimation error than that observed for the Prony method. The attenuation values in the normal population (49 subjects) were 0.44 +/- 0.03 dB/MHz/cm. Three hundred sixty-seven liver scans from 266 patients were evaluated. Hodgkin's lymphoma patients with liver involvement had attenuation values of 0.22 +/- 0.07 dB/MHz/cm. Low attenuation values also were observed for four patients with viral hepatitis (0.31 +/- 0.08 dB/MHz/cm). The detectability of other disease states was not increased by these global attenuation estimates; however, the results demonstrate possible potential uses for the proposed technique for the diagnosis of diffuse liver disease.

Hemodynamic and morphologic evaluation of the spleen after splenic vein ligation in the dog.

The splenic vein was ligated in ten dogs in order to evaluate the time course of changes in splenic size and to relate them to splenic arterial flow, splenic pressure and development of venous collaterals. Following ligation of the splenic vein, splenic size and venous pressure immediately rose in all dogs. Arterial flow to the spleen simultaneously fell in roughly inverse proportion to the elevation of venous pressure. During the following weeks, the splenic parenchymal pressure decreased to basline levels in all but one dog, as collateral veins developed through the gastric venous network to the portal vein. Splenic size gradually decreased toward normal in eight of the ten dogs. At the time of sacrifice, 8-16 weeks after splenic vein ligation, pathologic examination demonstrated fibrosis from healed infarction. Recent hemorrhage, indicating persistence of the congestive process, we also present, although difficult to explain in view of normal splenic parenchymal pressure.

Coronary calcium measurements by double helical computed tomography. Using the average instead of peak density algorithm improves reproducibility.

RATIONALE AND OBJECTIVES: Coronary calcium (CC) measured by fast computed tomography (CT) was proposed recently as a noninvasive method of monitoring the coronary atherosclerotic process. Assessment of the reproducibility of CC measurements (mainly interstudy variability) is essential for consistent interpretation of serial studies. METHODS: The authors scanned 74 patients (50 men and 24 women) twice on the same day to determine the interstudy variability of a new scoring algorithm, using the average instead of conventional peak CT density values. RESULTS: Nineteen patients had no calcium on either scan. In the remaining 55 patients, interstudy variability was decreased by 31% using the average algorithm (32%-23%; P < 0.001). CONCLUSIONS: Using the average instead of conventional peak density score provides better reproducible measurements of calcium by double helical CT.

Double-helical CT as a new tool for tracking of allograft atherosclerosis in heart transplant recipients.

RATIONALE AND OBJECTIVES: Tracking the progression of allograft atherosclerosis in heart transplant recipients is currently accomplished using invasive techniques. If its monitoring feasibility is demonstrated, spiral CT could be a non-invasive alternative for this objective. METHODS: Twenty-four consecutive heart transplant patients (21 men, 3 women, mean age 55 +/- 11 years) were scanned using double-helical CT. The first scan was performed 1.9 +/- 1.3 years after transplantation. After 2 years of follow-up, 4 patients died and the remaining 20 underwent a second scan. All scans were performed according to a previously reported double-helical CT protocol. RESULTS: The incidence of coronary calcification at the first scan was 4.2% (1/24); it increased to 40% (8/20) at the second scan (P < 0.001). Spiral CT identified new but very mild calcific deposits in seven patients with a mean total calcium score of 6.7 +/- 4.0. CONCLUSIONS: Double-helical CT is a viable tool to diagnose and track newly developed allograft atherosclerosis.

Takayasu arteritis in Israel--update.

Takayasu disease in our Israeli series consists of 56 patients, and has been detected only in Sephardic and oriental Jews as well as in Arabs and Bedouin. Suspicion of Takayasu disease should be raised whenever renal artery stenosis and involvement of the aorta and its branches occur in patients from oriental origin.

In vivo biomechanical behavior of the human heel pad during the stance phase of gait.

A technique is introduced for simultaneous measurements of the heel pad tissue deformation and the heel-ground contact stresses developing during the stance phase of gait. Subjects walked upon a gait platform integrating the contact pressure display optical method for plantar pressure measurements and a digital radiographic fluoroscopy system for skeletal and soft tissue motion recording. Clear images of the posterior-plantar aspect of the calcaneus and enveloping soft tissues were obtained simultaneously with the pressure distribution under the heel region throughout the stance phase of gait. The heel pad was shown to undergo a rapid compression during initial contact and heel strike, reaching a strain of 0.39 +/- 0.05 in about 150 ms. The stress-strain relation of the heel pad was shown to be highly non-linear, with a compression modulus of 105 +/- 11 kPa initially and 306 +/- 16 kPa at 30% strain. The energy dissipation during heel strike was evaluated to be 17.8+/-0.8%. The present technique is useful for biomechanical as well as clinical evaluation of the stress-strain and energy absorption characteristics of the heel pad in vivo, during natural gait.

Local tissue attenuation images based on pulsed-echo ultrasound scans.

This paper presents a novel technique for creating images of local tissue attenuation. The original conventional B scan is traversed, one pixel at a time. In the vicinity of each pixel, a uniform area is determined and average attenuation is computed utilizing an extended modified Prony approach. B scans of tissue mimicking phantoms and in vivo human liver scans are used in order to illustrate the performance of the proposed algorithm. The results show good agreement between estimated and known attenuation values. Clinical studies demonstrate significant potential of the proposed technique, in particular for diagnosis of diffuse liver disease.

Parathyroid sonography: diagnostic accuracy related to shape, location, and texture of the gland.

The sonographic features of 51 pathological parathyroid glands detected pre-operatively were analysed. Atypical texture was found in 23.5% and variation in shape in 15.6% of the cases. Cystic parathyroid glands are difficult to differentiate from thyroid cysts, and may be the cause of false positive diagnosis, as in three cases in this series. Topographic assessment showed a relatively low sensitivity in detecting disease in the right upper gland (50%) and in the upper mediastinum (70%). The decreased accuracy in these regions is probably because of the particular anatomical location of the right upper gland and sonographic limitations in screening the mediastinal region. Awareness by the radiologist and surgeon of the variations in texture and location may influence both diagnosis and intraoperative detection of the abnormal parathyroid gland.

CT findings in congenital anomalies of the spleen.

There is a wide range of congenital anomalies of the spleen. Some are common, such as splenic lobulation and accessory spleen. Other less common conditions, such as wandering spleen and polysplenia, have particular clinical significance. Radiologists need to be aware of the various congenital variants of the spleen in order to recognize clinically important anomalies and to avoid mistaking less significant ones for an abnormality. In this pictorial review, the embryology of congenital anomalies of the spleen as well as their appearance on CT are described, diagnostic pitfalls are identified and complications of the anomalies are discussed.

CT diagnosis of malpositioned chest tubes.

Insertion of a chest tube into the pleural space is standard management for various pleural disorders. Malpositioning of chest tubes in extrathoracic, intraparenchymal and mediastinal locations and in the fissures is common. Malpositioning results not only in inadequate drainage of air and fluid but may also result in increased morbidity and mortality. Diagnosis of a malpositioned tube is sometimes difficult to establish on a chest radiograph. CT, however, has proven to be extremely accurate in evaluating the position of a chest tube and has often provided additional valuable information with significant therapeutic impact.