Local contrast enhancement with

The local contrast enhancement algorithm (Eqs. 2 and 3) can be implemented with a simple device made from layers of conducting polymers (2). The device consists of an array of polymer grid triodes (3, 4) connected through a common grid which serves as a resistive network. 

An array of PGTs with a common grid (Figure 3) can perform local contrast enhancement like that simulated in Figure 1. Since the thin films which constitute the PGT array can be processed from solution, they can be layered directly on an array of photodetectors. Each node of the PGT array corresponds to one pixel of the image. 

Thus, local contrast enhancement, as described by Eqs. 2 and 3, can be directly implemented with the PGT array shown in Figure 3. The effective computation rates involved are impressive. The equivalent calculation implemented on a serial computer would require about 40 million mulitplications per second (256x256 pixels, 30 frames per second, 13x13 blurring using separable convolution). 

The final step required to demonstrate the validity of the polymer grid triode implementation of local contrast enhancement is to show that it computes the center-surround difference in Eq. 2. The equivalent circuit of the PGT demonstrated previously (3, 4) is that of two coupled diodes connected back-to-back, like that of a bipolar transistor (5). This is achieved by using semiconducting polymer in layers (2), (3 and (4). For the prototype array sketched in Figure 2c, layer (2) was fabricated with a material with sufficient conductivity to make an ohmic contact to the grid so that the equivalent circuit is simplified to a diode in series with a resistor. In the initial experiments, polyvinylcarbazole (PVK) was used for this resistor layer (2). In forward bias,... 

In contrast electromagnetic enhancement [6] relies on the intensification of the local electromagnetic field at the metal surface and the interaction of this localized electromagnetic field with the molecules close to, but not necessarily directly in contact with or chemisorbed at, the metal surface. The electromagnetic enhancement is of longer range than the chemical enhancement decaying over a distance of the order of 50 to 100 nm. 

The combination of contrast-enhanced MRI with photodynamic therapy based on the bifunctional conjugates can effectively localize tumor and estimate pharmacokinetics and tumor accumulation of the conjugate and provide... 

Better delineation ofectopic pancreas maybe seen on CT as a round mass with a variation of borders in the antral wall of the stomach a localization in the fundus is very unusual. After contrast injection the ectopic pancreatic tissue will enhance with a similar pattern to the normal pancreas. Cystic dilation of an ectopic pancreatic duct, ectopic pancreatic tissue in the perigastric fat, or malignant transformation of ectopic pancreas have been described but are rarely seen (Cho et al. 2000). 

In patients with locally advanced or recurrent cervical cancer, it is often necessary to exclude ureteral obstruction, which can be done on transverse T2-weighted images that also serve to assess the paraaortic lymph nodes. In addition, coronal T2-weighted turbo-spin echo (TSE) sequences enable excellent evaluation for possible urinary retention and require little extra time to acquire. In addition, contrast-enhanced MR urography can be performed to exclude tumor-induced hydronephrosis. 

Recurrent cervical cancer is associated with bone metastases (Fig. 7.39) in 15%-29% of patients at autopsy [ too, 103]. Typical locations are the bony pelvis as well as the lumbar and other vertebral bodies. Bone metastases in the ribs and extremities are less common. Skeletal metastases typically have an osteolytic character and originate from locally advanced or recurrent tumor in the pelvic sidewall or arise through retrograde tumor spread in patients with para-aor-tic lymph node metastasis [104]. Hematogenous dissemination to the skeleton occurs late. MRl with unenhanced and contrast-enhanced fat-saturated Tl-weighted sequences depicts bone metastases as hyperintense lesions in the low-intensity bone marrow with a high sensitivity. CT primarily shows the extent of osseous destruction. 

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