Peripheral enhancement

Angiotensin 11 can raise blood pressure in different ways, including (1) vasoconstriction in both the arterial and venous limbs of the circulation (2) stimulation of aldosterone secretion, leading to increased renal reabsorption of NaCl and water, hence an increased blood volume (3) a central increase in sympathotonus and, peripherally, enhancement of the release and effects of norepinephrine. 

Donepezil is primarily a reversible inhibitor of acetylcholinesterase with a long elimination half-life. It lacks the hepatotoxicity of tacrine but frequently causes nausea, vomiting and diarrhoea. These side effects, together with occasional bradycardia, sycope and changes in the sleep architecture, are directly associated with a central and peripheral enhancement of cholinergic function. At the present time, donepezil is the most widely prescribed anticholinesterase in the United States and Europe. 

In most cases of the thoracolumbar infarction, the swollen cord shows peripheral enhancement of the central gray matter. The concomitant enhancement of the cauda equina was reported first by Friedman and Flanders in 1992 (Fig. 17.8). This phenomenon is a characteristic finding in the course of spinal cord ischemia which might involve the cord itself and the ventral cauda equina as well, which is composed of motor fibre bundles (Amano et al. 1998). It indicates disruption of the blood-cord barrier as well as reactive hyperemia (Friedman and Flanders 1992 Amano et al. 1998). The differential diagnosis of contrast enhancement of the cauda equina includes transverse myelitis, bacterial or viral meningitis, and spinal metastasis. 

Buadu, L.D., Murakami, J., Murayama, S., et al. (1997) Patterns of peripheral enhancement in breast masses correlation of findings on contrast mediiun enhanced MRI with histologic features and tumor angiogenesis. Journal of Computer Assisted Tomography, 21, 421 30. 

On CT, a typical hemangioma will be seen as a mass with lower attenuation than the adjacent liver. After contrast injection it will show a peripheral enhancement followed by centripetal filling on late images. Some necrotic areas or calcifications might not enhance. More than 50% of hemangiomas will contain calcifications on CT. 

MRI of abdominal TB lymphadenopathy shows a variety of signal intensities and patterns of contrast enhancement and is described by De Backer et al. (2005). Mostly the signal intensities, in relation to abdominal wall muscle, are hyperintense on T2-WI with, in some cases, a hypointense peripheral rim and internal heterogeneity and hypo-/iso-intensity on Tl-WI, also occasionally with a peripheral rim, but then hyperintense or internal heterogeneity. Contrast-enhanced fat-suppressed Tl-WI demonstrate predominantly peripheral enhancement. 

Spatial Enhancement 72 Unsharp Masking 72 Adaptive Histogram Equalization 73 Multiscale Image Enhancement 74 Peripheral Enhancement 75... 

Fig. S.S. A raw digital mammogram from a Lorad Sele-nia processed using nonspatial processing and peripheral enhancement (a). Figure (b) shows results obtained by ap-...

Fig. 17.5a,b. Peritonitis in tuboovarian abscess. Transaxial CT sans in the mid pelvis (a, b). A left-sided tuboovarian abscess is located adjacent to the pelvic sidewall (arrow) between internal and external iliac vessels (a). It presents as a cystic peripherally enhancing lesion with a fluid-fluid level (arrowhead) presenting debris (a). Associated flndings include ascites, linear peritoneal enhancement (small arrows), and a netlike involvement of the pelvic fat and the omentum (arrow) (b)... 

At CT the penile thrombus presents as a tubular-shaped mass of fluid density with no internal enhancement and mild peripheral enhancement (Burkhalter and Morano 1985 Ptak et al. 1994). 

Contrary to gadolinium-based and to iodinated contrast agents, microbubbles do not diffuse out of the blood circulation. As a consequence, after intravenous microbubble administration fibrotic tissue shows no enhancement in all vascular phases. At contrast-enhanced ultrasonography, localized cavernosal tissue fibrosis presents as a circumscribed perfusion defect. Diffuse fibrotic changes present with inhomogeneous enhancement ofthe corpora cavernosa. Contrary to the normal cavernosal tissue, delayed peripheral enhancement of variable degree is often appreciable, probably by the presence of viable subalbugineal cavernosal tissue fed by peripheral vascular pathways, while poor or no contrast enhancement is appreciable in the central portion of the corpora cavernosa (Fig. 21.10). 

Fig. 21.10a,b. Cavernosal tissue scar andfibrosis. Axial scans obtained after intravenous microbubble injection, a Cavernosal tissue scar within the left corpus cavernosum presenting as a circumscribed area ( ) in which contrast enhancement is lacking, b Diffuse penile fibrosis following ischemic priapism. Peripheral enhancement ofthe corpora cavernosa is appreciable, while the central portion does not enhance... 

Fig. 10.1. Axial, venous phase, gadolinium-enhanced MRI of a patient with unresectable HCC showing a peripherally enhanced lesion (arrows) in the medial segment of the left lobe. Solid, well demarcated lesions such as this one respond better to TACE than do diffuse or multifocal lesions. Additionally, hypervascular tumors appear to respond better to TACE showing a higher degree of necrosis on follow-up MRI...

Fig. 10.7. Axial, gadolinium enhanced MRI of the liver of a patient with HCC shows a large, peripherally enhanced lesion (arrows) replacing the right lobe. The patient was unresectable owing to the size of the tumor. Decision was made to treat the patient with TACE for palliative reasons...

Murai M, Sugimoto M, Akita M (2013) Zinc-porphyrins functionalized with redox-active metal peripherals enhancement of d[small pi]-p[small pi] interaction leading to unique assembly and redox-triggered remote switching of fluorescence. Dalton Trans 42(45) 16108-16120... 

Smriga M, Saito H, Shibata S, Narui T, Okuyama T, Nishiyama N (1996) PC-2, Linear Homoglucan with a-Linkages, Peripherally Enhances the Hippocampal Long-term Potentiation. Pharmaceut Res 13 1322... 

Fig. 2.8a-d. Tjfpical haemangioma, a In the basal scan it appears as slightly hypodense area, b The lesion presents an initial peripheral enhancement during the arterial phase, c In the portal venous phase a globular centripetal enhancement is observed, d In the delayed phase the lesion shows an almost complete filling... 

Fig. 7.12a,b. Cj stic metastases from colon cancer. A 70-year-old man with colon cancer, a Portal venous-phase contrast-enhanced CT scan shows a cyst-like, hypoattenuating lesion, without peripheral enhancement, b The arterial phase CT image alone shows a peripheral rim-enhancement, typical of a metastatic lesion. The rapid growth of these metastases leads to cystic degeneration... 

Peripheral enhancement of the lesion followed by a central enhancement on contrast CT Contrast enhancement of the lesion on delayed scans (Freeny and Marks 1986)... 

On unenhanced CT the tumor appears as a homogeneous hypodense mass with or without calcifications which shows septal and peripheral enhancement. Delayed scanning may show greater enhancement (Dachman et al. 1987). 

Fig. 17.2a-c. Angiosarcoma. CT findings, a Unenhanced CT depicted hypodense lobulated masses white arrows) in the liver, b Arterial phase imaging shows non-enhancing lesions white arrows) with feeding artery (black arrowhead), c Low-density lesions are visualized with moderate peripheral enhancement white arrows) and feeding vessels black arrowhead) in venous phase imaging... 

The signal intensity features of angiosarcoma are similar to those that may be seen in hemangioma. Both tumors contain abundant blood-filled vascular spaces. However, the peripheral enhancement of angiosarcomas is not of the dense, discontinuous, and globular nature that is typically seen in cases of hemangioma (Marti-Bonmati et al. 1993). 

Similarly on CT scan both leiomyosarcomas and malignant fibrous histiocytoma have a similar appearance. A large non-calcified,hypodense,homogeneous mass is depicted, which exhibits heterogeneous peripheral enhancement after contrast medium administration. Non-enhancement corresponds to sites of necrosis with cystic and hemorrhagic spaces. Despite large tumors portal and hepatic veins are not involved in most cases (Pinson et al. 1994). 

Fig. 17.9a,b. Sarcoma. MR findings. Secondary non-calcified infiltration of the liver due to rectal sarcoma reveals hypoin-tense signal using Tl-weighted unenhanced imaging (a) and peripheral enhancement post-gadolinium administration (b). Inhomogeneous inner structure of the lesion is depicted with several hyperintense areas... 

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