Biomedical subjects

N Dogan

Publications and source records attributed to N Dogan.

14 recordsLinked to original sources

PubMed2003

Effectiveness of compensating filters in the presence of tissue inhomogeneities.

CT based 3D treatment planning systems (3DTPS) can be used to design compensating filters that, in addition to missing tissue compensation, can account for tissue inhomogeneities. The use of computer-driven systems provides a practical, convenient, and accurate method of fabricating compensating filters. In this work, we have evaluated a commercially available PAR Scientific DIGIMILL milling machine linked with FOCUS 3DTPS. Compensating filters were fabricated using refined gypsum material with no additives. Thus, filters were of manageable dimensions and were not sensitive to common machining errors. Compensating filters were evaluated using a homogeneous step phantom and step phantoms containing various internal inhomogeneities (air, cork, and bone). The accuracy of two planning algorithms used to design filters was experimentally evaluated. The superposition algorithm was found to produce better agreement with measurements than the Clarkson algorithm. Phantom measurements have demonstrated that compensating filters were able to produce a uniform dose distribution along the compensation plane in the presence of tissue inhomogeneity. However, the dose variation was greatly amplified in planes located beyond the inhomogeneity when a single compensated beam was used. The use of parallel-opposed compensated beams eliminated this problem. Both lateral and depth-dose uniformity was achieved throughout the target volume.

Biophysics↗

PubMed2003

Effects of deferoxamine on tissue lactate and malondialdehyde levels in cerebral ischemia.

In the present study, the effects of deferoxamine on tissue lactate and malondialdehyde (MDA) levels after cerebral ischemia in rabbits was studied. Rabbits were divided equally into three groups: group 1: sham-operated group; group 2: cerebral ischemia produced by clamping bilateral common carotid arteries for 60 min; and group 3: deferoxamine 100 mg/kg i.v. administered within 5 min after opening the clamps. EEG recordings were obtained in all groups before clamping and in group 2 and 3 60 min after clamping and 60 min after opening the clamps. One hour after opening the clamps and taking EEG recordings, brain cortices were resected and the concentrations of lactate and MDA were determined using the spectrophotometric enzymatic and thiobarbituric acid methods, respectively. There were significant differences between group 1 and the other groups in MDA and lactate levels (p < 0.05). There were no significant differences in lactate levels between groups 2 and 3. Preischemic EEG grades were the same in all groups. Preischemic and postischemic EEG values were significantly different (p < 0.05), but there were no significant differences between postischemic EEG grades in groups 2 and 3. There was also a correlation between postischemic EEG grades and lactate levels, but no correlation between postischemic EEG grades and MDA levels. These results demonstrate that cerebral ischemia leads to an increase in brain tissue lactate and MDA levels and deferoxamine suppresses the increase of MDA, but not lactate. Deferoxamine treatment caused no significant EEG changes. EEG grades correlated well with lactate levels.

Acute Disease↗

PubMed2001

Spinal toxoplasmic arachnoiditis associated with osteoid formation: a rare presentation of toxoplasmosis.

STUDY DESIGN: An extremely rare presentation of an isolated spinal toxoplasmic arachnoiditis is described. OBJECTIVE: To draw attention to the fact that spinal arachnoid membranes may be a potential reservoir for Toxoplasma gondii. SUMMARY OF BACKGROUND DATA: Central nervous system toxoplasmosis is a common manifestation in patients who are immunodeficient. Reports on the spinal toxoplasmosis are rare and focused on spinal cord involvement. METHODS: An adult patient presented with symptoms of spastic paraparesis that had begun 13 years before admission. Thoracic spinal magnetic resonance imaging showed small lesions in posterior subarachnoid space at Th7-Th8. A Th7-Th8 laminectomy was performed. Intradural-extramedullary lesions were excised. RESULTS: Clinical, immunologic, and pathologic examinations showed adhesive spinal arachnoiditis associated with osteoid formation caused by past toxoplasmic infection. There was no impairment of the immunologic defense system. CONCLUSION: Where no causative factor is found in serious spinal adhesive arachnoiditis, the possibility of spinal toxoplasmosis should also be investigated.

Adult↗

PubMed2001

Matching tomographic IMRT fields with static photon fields.

The matching of abutting radiation fields presents a challenging problem in radiation therapy. Due to sharp penumbra of linear accelerator beams, small (1-2 mm) errors in field positioning can lead to large (>30%) hot or cold spots in the abutment region. With head and neck immobilization devices (thermoplastic mask/aquaplast) an average setup error of 3 mm has been reported. Therefore hot or cold spots approaching 50% of the prescription dose may occur along the matchline. Although abutting radiation fields have been investigated for static fields, there is no reported study regarding matching of tomographic IMRT and static fields. Compared to static fields, the matching of tomographic IMRT fields with static fields is more complicated. Since IMRT and static fields are planned on separate treatment planning computers, the dose in the abutment region is not specified. In addition, commonly used techniques for matching fields, such as feathering of junctions, are not practical. We have developed a method that substantially reduces dose inhomogeneity in the abutment region. In this method, a "buffer zone" around the matchline was created and was included as part of the target for both IMRT and static field plans. In both fields, a small dose gradient (< or =3%/mm) in the buffer zone was created. In the IMRT plan, the buffer zone was divided into three sections with dose varying from 83% to 25% of prescription dose. The static field dose profile was modified using either a specially designed physical (hard) or a dynamic (soft) wedge. When these modified fields were matched, the combined dose in the abutment region varied by < or =10% in the presence of setup errors spanning 4 mm (+/-2 mm) when the hard wedge was used and 10 mm (+/-5 mm) with the soft wedge.

Biophysical Phenomena↗

PubMed2001

Effects of bupivacaine and ropivacaine on hemodynamic parameters in rabbits.

In the present study the toxic effects of ropivacaine and bupivacaine on the cardiovascular and respiratory systems of rabbits were studied. Both drugs were administered intravenously at doses of 0.5, 1, 2.5, 5 and 10 mumol/kg. The effects of the two drugs on blood pressure, ECG and respiration rate were evaluated by considering the changes occurring 30 sec after intravenous bolus injection. High doses (5 and 10 mumol/kg) of bupivacaine and ropivacaine significantly reduced the heart rate and systolic pressure (p < 0.05). Five and 10 mumol/kg of bupivacaine significantly reduced diastolic pressure (p < 0.05), but only the 10 mumol/kg dose of ropivacaine had the same effect. Low doses of bupivacaine and high doses of ropivacaine significantly increased the PR interval, QRS duration and QT interval (p < 0.05). The 5 mumol/kg dose of bupivacaine caused ventricular tachycardia in 3 of 6 rabbits, whereas ropivacaine caused tachycardia in 1 of 5 rabbits. Neither drug had a significant effect on respiration rate or blood gas values (p > 0.05). The results indicate that ropivacaine is less cardiodepressive and arrhythmogenic than bupivacaine.

Amides↗

PubMed2001

The role of K+ ions on the response to carbachol of calf coronary artery and cardiac vein during cooling.

The role of K+ ions on the vasoconstrictions induced by carbachol during cooling (28 degrees C) in the endothelium of a denuded calf coronary artery and cardiac vein (noncutaneous vessel) was studied. Carbachol (10(-9) - 3 x 10(-4) M) induced concentration-dependent contractions at both 37 degrees C and 28 degrees C. The sensitivity, but not the maximal response, of carbachol (10(-9) -3 x 10(-4) M) was significantly lower at 28 degrees C than at 37 degrees C. Cooling to 28 degrees C after treatment with tetraethylammonium (TEA, 10(-3) M) or ouabain (10(-5) M), after incubation in K+-free medium increased the sensitivity to carbachol in both preparations. The results suggest a role for K+ ions in the cooling-induced changes of noncutaneous vessels.

Animals↗

PubMed2000

A modified method of planning and delivery for dynamic multileaf collimator intensity-modulated radiation therapy.

PURPOSE: To develop a modified planning and delivery technique that reduces dose nonuniformity for tomographic delivery of intensity-modulated radiation therapy (IMRT). METHODS AND MATERIALS: The NOMOS-CORVUS system delivers IMRT in a tomographic paradigm. This type of delivery is prone to create multiple dose nonuniformity regions at the arc abutment regions. The modified technique was based on the cyclical behavior of arc positions as a function of a target length. With the modified technique, two plans are developed for the same patient, one with the original target and the second with a slightly increased target length and the abutment regions shifted by approximately 5 mm compared to the first plan. Each plan is designed to deliver half of the target prescription dose delivered on alternate days, resulting in periodic shifts of abutment regions. This method was experimentally tested in phantoms with and without intentionally introduced errors in couch indexing. RESULTS: With the modified technique, the degree of dose nonuniformity was reduced. For example, with 1 mm error in couch indexing, the degree of dose nonuniformity changed from approximately 25% to approximately 12%. CONCLUSION: Use of the modified technique reduces dose nonuniformity due to periodic shifts of abutment regions during treatment delivery.

Particle Accelerators↗

PubMed2000

Elimination of field size dependence of enhanced dynamic wedge factors.

Enhanced dynamic wedge factors (EDWF) are characterized by a strong field size dependence. In contrast to physical wedge factors, the EDWF decrease as the field size is increased: for 6 MV 60 degrees wedge, the EDWF decreases by 50% when the field size is increased from 4 x 4 cm2 to 20 x 20 cm2. A method that eliminates the field size dependence of EDWF was developed and investigated in this work. In this method, the wedged field shape is determined by a multileaf collimator. The initial position of the moving Y jaw is determined by the field size and the stationary Y jaw is kept fixed at 10 cm for field sizes < or = 20 cm in the wedged direction. For all other fields, the stationary Y jaw setting is determined by the field size. The modified method results in EDWF that are independent of field size, with no change in the wedge dose distribution when compared with the conventional use of EDW.

Models, Statistical↗

PubMed2000

Improvement of tomographic intensity modulated radiotherapy dose distributions using periodic shifting of arc abutment regions.

Based on the study of treatment arc positioning versus target length, a method that allowed periodic shift of arc abutment regions through the course of intensity modulated radiotherapy (IMRT) was developed. In this method, two treatment plans were developed for the same tumor. The first plan contained the original target (Planning Target Volume as defined by radiation oncologist) and the second one contained a modified target. The modification of the original target consisted of simply increasing its length, adding a small extension to it, or creating a distant pseudo target. These modifications cause arc abutment regions in the second plan to be shifted relative to their positions in the first plan. Different methods of target modification were investigated because in some cases (for instance, when a critical structure might overlap with the target extension) a simple extension of the target would cause an unacceptable irradiation of the sensitive structures. The dose prescribed to the modified portion of the target varied from 10% to 100% of the original target dose. It was found that a clinically significant shift (> or =5 mm) in abutment region locations occurred when the dose prescribed to the extended portion of the target was > or =95% of the original target dose. On the other hand, the pseudo target required only approximately 10% to 20% of the original target dose to produce the same shift in arc positions. Results of the film dosimetry showed that when a single plan was used for the treatment delivery, the dose nonuniformity was 17% and 25% of the prescribed dose with 0.5 and 1 mm errors in couch indexing, respectively. The dose nonuniformity was reduced by at least half when two plans were used for IMRT delivery.

Dose-Response Relationship, Radiation↗

PubMed1996

[Optimizing a conventional documentation system on the surgical intensive care unit--a contribution to cost reduction and preventive quality management?].

In Intensive Care Units (I.C.U.), the lack of staff and funds require the mobilisation of organisational reserves in order to ensure high-quality patient care. Traditional occupational-group organised documentation systems are burdened with lack of clarity, limited utilisation by the staff, insufficient information content and difficulties in synoptic patient monitoring. They cannot meet the demands of modern intensive-care medicine. At the inauguration of our Surgical I.C.U. in June 1992, an occupational-group oriented documentation system was introduced and put into operation. Because of negative repercussions on patient care, it was replaced by a patient-centered, conventional prescription and documentation system in April 1993. In April 1994, an evaluation of the patient-centered system was carried out. We report on our initial problem analysis, the subsequent developmental and introductory phases, and the results after having used the system in our I.C.U. for one year. Data condensation, standardised data recording, as well as structured prescription, examination, assessment and decision processes, saved 730 working hours for medical and nursing staff per year, reduced the cost for documentation materials by 58% and improved the extent of data recording. In our experience, improving a conventional documentation system is a suitable instrument to support cost reduction and preventive internal quality management in the I.C.U.

Cost Savings↗

PubMed1995

Protective effects of cilazapril against free radical injury in myocardial ischaemia-reperfusion.

Cilazapril is a prodrug which is rapidly hydrolysed to the pharmacologically active cilazaprilat following absorption to the bloodstream. In clinical pharmacological studies, administration of cilazapril resulted in potent, reversible, selective and competitive angiotensin converting enzyme inhibition. In this study, we have examined the protective effect of cilazapril on a myocardial ischaemia-reperfusion model by using different parameters of lipid peroxidation and protein oxidation. We have observed increased levels of diene conjugates, carbonyls and malondialdehyde as well as protein carbonyls after ischaemia-reperfusion, whereas protein sulphydryl groups were decreased. Our results clearly demonstrate that cilazapril, a non-sulphydryl, long-acting angiotensin converting enzyme inhibitor, has free-radical-scavenging potential in a model comparable to the clinical situation observed in humans.

Animals↗

PubMedDate not supplied

A modified technique for RF-LCF interstitial hyperthermia.

To provide uniform heating of a tumour, it is necessary to establish sufficient volumetric control of power deposition. The interstitial Radio-Frequency Localized Current Field (RF-LCF) technique may provide such control when segmented electrodes are used. The length of segments is equal to 1-1.5 cm. Each segment is connected to a separate power source. However, this technique requires an additional implant for interstitial radiotherapy, because the lumen of segmented electrodes is filled with wires necessary to connect each segment to a separate power source. In this work, a modified method of implant that allows delivery of sequential and concomitant controlled thermoradiotherapy was investigated. In this method, each segmented electrode is surrounded by four continuous electrodes. Continuous electrodes pass through vertices of 1.5 x 1.5 cm square and a segmented electrode passes through the centre of the square. The distance between segmented and continuous electrodes is 1.06 cm. The electric field induced between an electrically interacting segment and continuous electrodes is concentrated primarily between this segment and its projection on continuous electrodes. Therefore, control of temperature distribution achieved with a modified implant is similar to that achieved with an implant containing only segmented electrodes. For temperature control during treatment, plastic catheters are inserted at a 0.5 cm distance from each segmented electrode. Temperature is monitored using multisensor temperature probes. The continuous electrodes are also used for placement of radioactive sources. The lateral distance between radioactive sources is equal to 1.5 cm. Besides allowing a sequential and concomitant thermoradiotherapy, the modified method is simpler to implement because it uses several fold less amount of segmented electrodes and power sources.

Biosensing Techniques↗

PubMedDate not supplied

Nonadrenergic, noncholinergic responses of the rabbit detrusor smooth muscle and the role of L-arginine/nitric oxide pathway in these responses.

In the present study, nonadrenergic, noncholinergic (NANC) responses of rabbit detrusor smooth muscle and the possible involvement of the L-arginine/nitric oxide (L-ARG/NO) pathway was investigated. In the presence of atropine (10(-6) M) and guanethidine (10(-5) M), frequency-response curves were obtained by stimulating tissue with 10-sec trains at increasing frequencies (1-10 Hz) with 3-min intervals between stimulations. Electrical field stimulation (EFS) evoked a biphasic response in rabbit detrusor smooth muscle, consisting of an initial contraction followed by relaxation. ATP desensitization significantly inhibited contractions. L-NAME (10(-5) M) increased the contractions by a maximum of 33 +/- 5% at 1 Hz, 37 +/- 5% at 2 Hz, 18 +/- 4% at 4 Hz, 20 +/- 3% at 8 Hz and 15 +/- 4% at 10 Hz. In detrusor preparations, exposure to L-NAME (NG-nitro-L-arginine methyl ester, 10(-5) M) significantly reduced the maximal relaxation to electrical stimulation to 7 +/- 3% of the control. In the presence of L-ARG (10(-4) M), contractions induced by electrical field stimulation (EFS) at 1, 2, 4, 8 and 10 Hz were reduced by 20 +/- 4, 24 +/- 3, 25 +/- 3, 20 +/- 3 and 30 +/- 5%, respectively. Exposure to L-ARG (10(-4) M) significantly increased the maximal relaxation to electrical stimulation to 52 +/- 5% of the control. Exogenously applied ATP (10(-5)-10(-2) M) to rabbit detrusor muscle resulted in contractions while sodium nitroprusside (10(-7)-10(-3) M) caused concentration-dependent relaxation. These results suggest that nitric oxide (NO) acts as an inhibitory NANC neurotransmitter in the rabbit detrusor smooth muscle. Additionally, NANC contractions mediated by ATP released from NANC nerves, may be masked by the L-ARG/NO pathway in this tissue.

Adenosine Triphosphate↗

PubMedDate not supplied

Nonadrenergic, noncholinergic responses of the human colon smooth muscle and the role of K+ channels in these responses.

The aim of the present study was to investigate the possible role of nitric oxide (NO) as a nonadrenergic, noncholinergic (NANC) mediator in human colon smooth muscle in vitro and to examine its possible interactions with K+ channels. In the presence of atropine (10(-6) M) and guanethidine (10(-5) M), electrical field stimulation (EFS, 1-10 Hz, 0.3 msec, 50 V) for 10 sec induced relaxations which were inhibited by tetrodotoxin (10(-6) M). In the presence of NG-nitro-L-arginine methyl ester (L-NAME, 10(-4) M), relaxations induced by EFS at 1, 2, 4, 8 and 10 Hz were reduced by 38.7 +/- 4.3, 31.5 +/- 3.8, 54.3 +/- 5.4, 59.8 +/- 4.5 and 68.6 +/- 5.3%, respectively. The relaxations inhibited by L-NAME were restored by the preincubation of L-arginine (L-ARG, 10(-3) M) at all frequencies tested. D-Arginine (D-ARG, 10(-3) M) had no effect. Tetraethylammonium (TEA, 10(-4) M) or glibenclamide (10(-6) M) significantly decreased the relaxations induced by EFS. Exogenously applied sodium nitroprusside caused concentration-dependent relaxation with maximum relaxation observed with 10(-3) M. TEA (10(-4) M) and glibenclamide (10(-6) M) significantly depressed the maximum response to sodium nitroprusside. In conclusion, our data indicate that NO is involved in NANC nerve-mediated relaxation in the human colon smooth muscle and the relaxant responses to endogenously released or exogenously applied NO are mediated, in part, by activation of calcium-dependent and ATP-sensitive K+ channels.

Colon↗