Measurement of relative lung perfusion with electrical impedance and positron emission tomography: an experimental comparative study in pigs.

BACKGROUND: Electrical impedance tomography (EIT) with indicator dilution may be clinically useful to measure relative lung perfusion, but there is limited information on the performance of this technique. METHODS: Thirteen pigs (50-66 kg) were anaesthetised and mechanically ventilated. Sequential changes in ventilation were made: (i) right-lung ventilation with left-lung collapse, (ii) two-lung ventilation with optimised PEEP, (iii) two-lung ventilation with zero PEEP after saline lung lavage, (iv) two-lung ventilation with maximum PEEP (20/25 cm H2O to achieve peak airway pressure 45 cm H2O), and (v) two-lung ventilation under unilateral pulmonary artery occlusion. Relative lung perfusion was assessed with EIT and central venous injection of saline 3%, 5%, and 10% (10 ml) during breath holds. Relative perfusion was determined by positron emission tomography (PET) using 68Gallium-labelled microspheres. EIT and PET were compared in eight regions of equal ventro-dorsal height (right, left, ventral, mid-ventral, mid-dorsal, and dorsal), and directional changes in regional perfusion were determined. RESULTS: Differences between methods were relatively small (95% of values differed by less than 8.7%, 8.9%, and 9.5% for saline 10%, 5%, and 3%, respectively). Compared with PET, EIT underestimated relative perfusion in dependent, and overestimated it in non-dependent, regions. EIT and PET detected the same direction of change in relative lung perfusion in 68.9-95.9% of measurements. CONCLUSIONS: The agreement between EIT and PET for measuring and tracking changes of relative lung perfusion was satisfactory for clinical purposes. Indicator-based EIT may prove useful for measuring pulmonary perfusion at bedside.

Engineering near-infrared single-photon emitters with optically active spins in ultrapure silicon carbide.

Vacancy-related centres in silicon carbide are attracting growing attention because of their appealing optical and spin properties. These atomic-scale defects can be created using electron or neutron irradiation; however, their precise engineering has not been demonstrated yet. Here, silicon vacancies are generated in a nuclear reactor and their density is controlled over eight orders of magnitude within an accuracy down to a single vacancy level. An isolated silicon vacancy serves as a near-infrared photostable single-photon emitter, operating even at room temperature. The vacancy spins can be manipulated using an optically detected magnetic resonance technique, and we determine the transition rates and absorption cross-section, describing the intensity-dependent photophysics of these emitters. The on-demand engineering of optically active spins in technologically friendly materials is a crucial step toward implementation of both maser amplifiers, requiring high-density spin ensembles, and qubits based on single spins.

[Photodynamic therapy with verteporfin in occult choroidal neovascularization in age-related macular degeneration]. / Photodynamische Therapie mit Verteporfin bei okkulter chorioidaler Neovaskularisation im Rahmen der altersbezogenen Makuladegeneration.

OBJECTIVE: We investigated retrospectively the clinical outcome of photodynamic therapy (PDT) with verteporfin (Visudyne) in patients with exudative age-related macular degeneration (ARMD) and subfoveal occult choroidal neovascularization (OCN). METHODS: 77 consecutive patients (90 eyes) with OCN were retrospectively analysed using a standardised protocol. It included best corrected visual acuity (BCVA) pre- and post-PDT, greatest linear dimension of OCN (GLD), ophthalmoscopic findings, optical coherence tomography (OCT), fundus photography and fluorescein angiography (FAG). The findings were descriptively analysed by Spearman rank correlation and cross-tabulation. RESULTS: Age ranged from 52 to 92 years (median: 79 years). 7 (8 %) of 90 PDT eyes gained > or = 2 lines, 67 (74 %) eyes stabilised with +/- 1 line. 17 eyes (18 %) showed a deterioration with loss of > or = 2 lines. BCVA of all cases was pre-PDT 0.33 (+/- 0.2), post-PDT 0.27 (+/- 0.2, p < 0.05), in the improvement group pre-PDT 0.4, post-PDT 0.7 in the stable cases pre-/post-PDT 0.3 and in the deterioration group pre-PDT 0.4 and post-PDT 0.2. GLD of all cases was pre-PDT 3.91 mm (minimum: 0.76 mm, maximum: 5.43 mm). From 86 eyes with OCT follow-up of at least 3 months 51 (60 %) had dry macula after last PDT and 35 (40 %) persistent macular edema (ME) in OCT. In 21 eyes (23 %) with leakage of fluorescein after last PDT, treatment was terminated. 10 eyes (47 %) had retinal angiomatous proliferation stage III, of these, 6 eyes presented with retinochoroidal anastomoses. 4 eyes (18 %) showed after PDT retinochoroidal anastomoses, 2 (10 %) vitreomacular traction in epiretinal membrane of the macula, 2 (10 %) had a tear of the retinal pigment epithelium, 1 (5 %) eye had a gain of GLD > 7200 microm, in 1 eye (5 %) BCVA was < 0.05 and in 1 eye (5 %) treatment was stopped at request of the patient. CONCLUSIONS: According to our study PDT might be helpful in the treatment of OCN in ARMD patients for stabilisation but not for improvement of BCVA. Results from large multicentre studies show that concerning BCVA ranibizumab (Lucentis) is superior to PDT in OCN. Further studies are required to investigate the outcome of combined therapy with PDT and VEGF inhibitors for reducing the number of treatments or the number of recurrences of choroidal neovascularisation.