Lutetium oxyorthosilicate block detector readout by avalanche photodiode arrays for high resolution animal PET.

Avalanche photodiodes (APDs) have proven to be useful as light detectors for high resolution positron emission tomography (PET). Their compactness makes these devices excellent candidates for replacing bulky photomultiplier tubes (PMTs) in PET systems where space limitations are an issue. The readout of densely packed, 10 x 10 lutetium oxyorthosilicate (LSO) block detectors (crystal size 2.0 x 2.0 x 12 mm3) with custom-built monolithic 3 x 3 APD arrays was investigated. The APDs had a 5 x 5 mm2 active surface and were arranged on a 6.25 mm pitch. The dead space on the edges of the array was 1.25 mm. The APDs were operated at a bias voltage of approximately 380 V for a gain of 100 and a dark current of 10 nA per APD. The standard deviation in gain between the APDs in the array ranged from 1.8 to 6.5% as the gain was varied from 50 to 108. A fast, low-noise, multi-channel charge sensitive preamplifier application-specific integrated circuit (ASIC) was developed for the APD readout. The amplifier had a rise time of 8 ns, a noise floor of 515 e- rms and a 9 e- pF(-1) noise slope. An acquired flood image showed that all 100 crystals from the block detector could be resolved. Timing measurements with single-channel LSO-APD detectors, as well as with the array, against a plastic scintillator and PMT assembly showed a time resolution of 1.2 ns and 2.5 ns, respectively. The energy resolution measured with a single 4.0 x 4.0 x 10 mm3 LSO crystal, wrapped in four-layer polytetrafluoroethylene (PTFE) tape and coupled with optical grease on a single APD of the array, yielded 15% (full width at half maximum, FWHM) at 511 keV. Stability tests over 9 months of operation showed that the APD arrays do not degrade appreciably. These results demonstrate the ability to decode densely packed LSO scintillation blocks with compact APD arrays. The good timing and energy resolution makes these detectors suitable for high resolution PET.

Intraoperative coronary artery dilatation with angioscopic guidance.

The use of intraoperative balloon dilatation during coronary artery bypass surgery has been limited due to relatively unpredictable and potentially damaging results. The development of fiberoptic angioscopy permits safe visualization of the interior of coronary arteries and may be a valuable adjunct to intraoperative balloon dilatation. A 56-year-old male underwent four vessel coronary grafting with progressive intraoperative balloon dilatation of a second more distal stenosis of the left anterior descending coronary artery. Angioscopy was used to determine optimal balloon sizing and allowed visualization of associated intimal changes that occurred during the procedure, resulting in a successful outcome for this patient.

Intraoperative angioscopy for coronary bypass surgery.

Despite advances in coronary artery surgery, technical abnormalities remain a significant cause of early graft closure. The development of small fiberoptic angioscopes now allows direct intravascular magnified examination. Seventy-five distal anastomoses and vein grafts, and five selected coronary arteries were examined with 0.8- to 2.5-mm diameter angioscopes introduced through the proximal vein graft while irrigating with clear cardioplegia. Angioscopic findings were correlated with angiographic data, vessel morphology, graft flow, and postoperative course. Satisfactory images were obtained in 72 of 75 anastomotic inspections. Each examination took less than 2 minutes and required less than 100 cc of flush. Angioscopic abnormalities that did not require revision were noted in 17 of 72 anastomoses; intimal flaps in 9, thrombus on posterior wall plaque in 4, intimal irregularities in 4, bucking of posterior wall in 3, and valve near anastomoses in 1. No outflow obstruction nor misplaced sutures were noted. Average flow rate through the grafts with anastomotic angioscopic abnormalities was 33 cc/min versus 40 cc/min in the remaining grafts. However, regression analysis revealed that low-graft flow was correlated with vessel size and runoff but was not with angioscopic findings. Intracoronary angioscopy revealed discrepancy with angiographic findings in 4 of the 5 examinations. No complications occurred as a result of angioscopy. No graft closure has occurred during early follow-up. Intraoperative angioscopy can be done with minimal alteration of the usual routine. The 24% occurrence of minor angioscopic abnormalities did not appear to compromise graft flow or early patency.

Left main coronary artery reconstruction after radiation therapy.

We report the case of a patient with radiation-induced left main coronary stenosis in whom an internal mammary artery bypass graft failed a 5 years and necessitated direct left main reconstruction.

Telephone follow-up programs as creative nursing interventions.

Perinatal nurses responded to their own concerns and to those expressed by their patients with the development of a follow-up program. This program proposed a way to extend comprehensive care and teaching after hospital discharge. A valuable approach in postpartum, this program also lends itself to areas such as the NICU and PICU.

Intraoperative coronary angioscopy: development of practical techniques.

Techniques and equipment for intraoperative coronary angioscopy were studied in the coronary arteries and cardiac veins of excised and in vivo animal hearts. These studies then allowed development of safe, practical techniques for human clinical use. In coronary artery bypass operations, multichannel angioscopes of 2.3 to 2.8 mm diameter gave the best results for examinations of the bypass vein and anastomosis, whereas smaller optical fibers of 1 mm diameter were required for inspection of the native coronary artery. Abnormalities were detected in 11 of 48 (23%) coronary bypass anastomoses, and significant discrepancy in the degree of coronary artery stenosis as compared with the preoperative angiogram was revealed in 2 patients. The authors concluded that a new design of ultrafine, multichannel angioscope would be more suitable to the different requirements for inspection of both the anastomosis and the recipient artery.