Peter Mueller

Multiplexed local charge storage, close to quantum processors at cryogenic temperatures could generate a multitude of control signals, for electronics or qubits, in an efficient manner. Such cryogenic electronics require generating quasi-static control signals with small area footprint, low noise, high stability, low power dissipation and, ideally, in a multiplexed fashion to reduce the number of input/outputs. In this work, we integrate capacitors with cryogenic high-electron mobility transistor (HEMT) arrays and demonstrate quasi-static bias generation using gate pulses controlled in time and frequency domains. Multi-channel bias generation is also demonstrated. Operation at 4 K exhibits improved bias signal variability and greatly reduced subthreshold swing, reaching values of ~6 mV/decade. Due to the very low threshold voltage of 80 mV at 4 K and the steep subthreshold swing, these circuits can provide an advantage over the silicon-based complementary metal-oxide-semiconductor equivalents by allowing operation at significantly reduced drive bias in the low output voltage regime <1 V. Together with their high-speed operation, this makes HEMTs an attractive platform for future cryogenic signal generation electronics in quantum computers.

We report the indications, methods, and complications of percutaneous gastrostomy/gastrojejunostomy (G/GJ) in patients with voluminous ascites. Following institutional review board approval, 69 patients (14 male, 55 female, mean age 58±12 years, range 32-89 years) who underwent percutaneous G/GJ with paracentesis were identified from a prospectively acquired database. Electronic medical record data extracted included diagnosis, method of G/GJ insertion, clinical course, and complications, which were graded by The Society of Interventional Radiology (SIR) criteria. Statistics were performed using Graphpad Instat. Sixty-six G and three GJ catheters were placed in 62 patients with malignant and 7 patients with benign disease; 47 procedures were conducted using fluoroscopy and 22 using computed tomography (CT; 10 patients had failed fluoroscopy). Sixty-six patients had 1980±1371 mL (range, 20-5000 mL) ascites drained (more in males, p=0.01) 0.8±1.6 days (range, 0-5 days) prior to placement. Forty-one patients had significantly less ascites (1895±1426 mL; range, 100-5400 mL) drained after G/GJ (p>0.0.5). Mean survival after insertion was 43±57 days (range, 1-252 days) among 38 patients for whom data were available. Fifty-six patients had a mean postprocedure hospital stay of 8.6±8.4 days (range, 0-45 days); 3 were outpatients and 10 patients died in the hospital. Successful gastropexy was confirmed on subsequent cross-sectional imaging in 22 of 25 patients. There were 25 tube maintenance issues that included catheter displacement and leakage, one patient experienced hemorrhage, and there were two deaths. All except one patient had satisfactory gastrostomy function. Effective G/GJ placement is possible in most patients with voluminous ascites provided ascites is drained and gastrocutaneous fistula formation occurs. Caution is advised; placement is generally for fragile terminal patients, and fluoroscopy or CT guidance is required.

Percutaneous biopsy is an emerging modality in the study of small renal masses. We correlated biopsy pathology results with surgical pathology specimens to investigate the concordance of the pathologic diagnoses.