Journal of european ceramic society

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Приведенная ссылка Cycles In-vivo animal studies initially demonstrated adequate cell kill in normal tissue employing a single freeze-thaw cycle (Weber et al, 1997).

However, further studies on implanted tumor cells in mice, then in dogs, found детальнее на этой странице multiple freeze-thaw cycles promoted a larger and more adequate area of liquefactive necrosis, improving subsequent cure rates (Neel et al, 1971; Woolley et al, 2002).

Therefore, when treating renal malignancies, the current recommendation is to perform a double freeze-thaw cycle to ensure complete cellular death. The thawing process is also instrumental in cellular death and may be performed in a passive or active manner.

Passive thawing, which relies on the ice ball melting without any intervention after the cessation of argon gas through the cryoprobe, is more time-consuming journal of european ceramic society active thawing, where helium gas (rather than argon) is forced through the cryoprobe creating a warming effect secondary to the Joule-Thomson principle. Although clearly more efficient, there are conflicting data on whether an active thaw is as effective as a passive thaw (Woolley et al, 2002; Klossner et al, 2007).

In addition to decreasing operating room time, an active thaw during at least the second thaw cycle may allow the surgeon to more rapidly address post-treatment bleeding (White and Kaouk, journal of european ceramic society. Duration of Treatment The journal of european ceramic society of treatment to produce complete cellular death in humans is unknown. Auge читать статью colleagues (2006) performed a prospective study in nine female farm pigs with CA performed for 5, 10, or 15 minutes.

Although bumex lesions demonstrated complete cellular necrosis 5 mm from the probe, only animals treated for 10 or 15 minutes had necrosis extending 10 mm or more beyond the probes.

Furthermore, animals treated for only 5 minutes had excessive bleeding, whereas those treated for 15 minutes had an increased risk for tumor fracture and subsequent hemorrhage. Based on these findings, most contemporary series use a freeze cycle of 8 to 10 minutes (Breen et al, 2013; Kim et al, 2013).

RADIOFREQUENCY ABLATION Background and Mode of Action Radiofrequency ablation (RFA) refers to the use of radiofrequency energy to heat tissue to the point of cellular death. RFA uses monopolar alternating electric current that is delivered directly into the 1486 PART X Neoplasms of the Upper Urinary Tract target tissue at a frequency of 450 to 1200 kHz, leading to vibration of ions within tissue and resulting in molecular friction and heat production.

Increasing temperature within the target tissue leads to cellular protein denaturation читать статью cell membrane disintegration (Hsu et al, 2000; Tracy et al, 2010). Importantly, heat is not directly supplied by the probe itself, but rather by the agitation of ions within the tissue (Cosman et al, 1984). Without a clear understanding of the technology and an inability to effectively control the energy, the use of radiofrequency energy in surgery did not become more mainstream until 1928, when Cushing and Bovie developed the electrocautery knife.

These principles led to further development of RFA and opened the door for use in a broader number of surgical journal of european ceramic society (Organ, 1976). In 1990 two individual groups of researchers simultaneously reported the нажмите сюда of probes that could be used for percutaneous читать (McGahan et al, 1990; Rossi et al, 1990).

These probes consisted of a layer of insulation down to journal of european ceramic society exposed metal tip, which allowed for percutaneous passage of the needle to deeper target journal of european ceramic society. Using these needles, the amount of tissue destruction could be controlled along the central axis of the lesion by adjusting the length of the exposed, uninsulated portion of the needle.

Although effective in water is along the long axis of the lesion, these initial probes were limited in their ability to create circumferential tissue damage, preventing their use in lesions greater than 1.

Further refinements using these initial designs led to the development of modern RFA generators and probes, which are capable of treating larger and more complex lesions. Variations in Radiofrequency Ablation Equipment RFA can be performed with either a temperature-based or impedance-based monitoring system.

Journal of european ceramic society systems work by measuring tissue temperatures at the tip of the electrode and are based on achieving a specific temperature for a given period. These systems accurately measure the temperature of the tissue at the electrode tip; however, they do not measure the temperature of the surrounding parenchyma. Alternatively, impedance-based systems measure the tissue impedance (resistance to alternating current) at the electrode tip and are based on achieving a predetermined impedance level that indicates complete tissue journal of european ceramic society. Although these systems are able to measure actual tissue desiccation at the electrode tip, they have been associated with incomplete ablation in animal models (Gettman, 2002a).

There are no explicit clinical data that support the superiority of impedance or temperature-based systems. The original ablation probes, which were designed as single electrode monopolar probes controlled by varying the exposed uninsulated tip, were capable of treating tumors no greater нажмите для деталей 2 cm (McGahan et al, 1993).

Therefore the treatment of larger tumors or the acquisition of an adequate tumor margin often required additional probes or re-treatment of overlapping regions. Multiple systems have been developed in http://longmaojz.top/louisa-johnson/testosterone-250.php attempt to achieve a larger overall treatment volume.

These tines are deployed in an umbrella shape to create a spherical lesion. When high impedance is encountered at one prong, current is redirected to areas of lower impedance. Clinical validation studies have suggested more complete necrosis and superior treatment outcomes with multitine electrodes (Rossi et al, 1998; Curley et al, 2000; Rehman et al, 2004). As tissue desiccation increases in the target lesion, the charring effect (carbonization) on tissue leads to increased impedance and resistance to the alternating current of the electrode, limiting the size of the ablation zone with a single electrode journal of european ceramic society less than 4 cm.

Radiofrequency energy also can be delivered through either bipolar or monopolar electrodes. Compared to traditional monopolar radiofrequency devices, which work based on electrical transmission through the exposed probe tip with dissipation больше на странице a grounding pad on the skin of the patient, bipolar radiofrequency devices journal of european ceramic society current between two separate electrodes (one active and one negative), within the target tissue.

The purported advantage of bipolar energy is that significantly higher temperatures are induced compared with those of monopolar devices (Nakada Diprolene AF (Betamethasone)- FDA al, 2003).

Посетить страницу источник addition, heat is generated not only at the active probe but also adjacent to the ground needle and between the two electrodes (McGahan et al, 1996), resulting in a focus of coagulation necrosis that is larger than with a conventional monopolar electrode.

The use of two separate electrodes, however, produces an elliptical area of coagulation necrosis rather than spherical; journal of european ceramic society most renal tumors are spherical, this technology has not been widely adapted for RFA of renal masses.

Treatment Temperature The ability of RFA to ablate the target tissue relies on power delivered to the probe, the maximum temperature obtained, and the duration of the ablation (McGahan and Dodd, 2001). As stated, alternating radiofrequecy current creates cellular agitation and, as a result of electrical impedance of the tissue, local heating. Provided that electrical impedance remains low, an expanding sphere of tissue damage emanates outward from the journal of european ceramic society probe.

If current is administered too rapidly or the amount of radiofrequency energy applied is too high, charring occurs, which reduces the water content of the tissue. Charring and dehydration then may lead to increased electrical impedance, blocking energy transfer and halting benet plus heating process (Djavan journal of european ceramic society al, 2000; Finelli et al, 2003).

It is also important to reach a minimum target temperature at which cellular death occurs.

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Comments:

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