Human health and medicine

Quadrantectomy

Quadrantectomy is a breast-conserving operation for early breast cancer that removes the entire tumor-bearing quadrant with skin and fascia, developed in Milan by Umberto Veronesi and validated against radical mastectomy with equivalent survival.

Quadrants and regions of abdomen

Quadrants and regions of abdomen: two topographic systems dividing the abdominal surface. Four quadrants (RUQ, LUQ, RLQ, LLQ) from planes through the umbilicus at L3-L4; nine regions from midclavicular, subcostal, and transtubercular planes.

Quadratus lumborum block

The quadratus lumborum block is an ultrasound-guided fascial plane block injecting local anesthetic near the quadratus lumborum muscle to relieve pain after abdominal and hip surgery.

Quadratus lumborum muscle

Quadratus lumborum: posterior abdominal wall muscle between the iliac crest, 12th rib, and L1-L4 transverse processes; weak lumbar stabilizer, inspiration accessory, and target of the quadratus lumborum block.

Quadriceps

Quadriceps femoris, the four-headed anterior thigh muscle group (rectus femoris, vastus medialis, lateralis, intermedius), the primary knee extensor innervated by the femoral nerve L2-L4, central to patellofemoral pain rehabilitation.

Quadricuspid aortic valve

Quadricuspid aortic valve (QAV), a rare congenital four-cusp aortic valve (0.013-0.043% prevalence), types A-G, usually causing aortic regurgitation; diagnosed by TEE, surgery in about half of patients.

Quadrivalent influenza subunit vaccine

Quadrivalent influenza subunit vaccine (慧尔康欣, Hui Erkang Xin), China's first quadrivalent subunit flu vaccine by Jiangsu Ab&B Bio-Tech, NMPA-approved May 2023, covering H1N1, H3N2, BV, BY with 15 µg HA per strain.

Quadruplet pregnancy

Quadruplet pregnancy, a higher-order multiple gestation with four fetuses (ICD-11 JA80.2, ICD-10 O30.2), occurs naturally about 1 in 700,000 conceptions and carries high risks of preterm delivery, maternal complications, and neonatal loss.

Qualitative platelet defects

Qualitative platelet defects: inherited or acquired disorders of platelet function with normal counts, causing mucocutaneous bleeding. Includes Glanzmann thrombasthenia (αIIbβ3), Bernard-Soulier syndrome (GPIb-IX-V), P2Y12 and GPVI defects.

Quality Improvement

Quality improvement (QI): systematic, continuous approach to improving healthcare quality and patient outcomes using methods such as PDSA cycles, Lean, and Six Sigma adapted from industry; distinct from but complementary to implementation science.

Quality of Health Care

Quality of health care: the degree to which health services increase desired outcomes consistent with professional knowledge (IOM 1990). Covers Donabedian's structure–process–outcome model, IOM six aims, quality indicators, and OECD/CMS measurement frameworks.

Quantitative computed tomography

Quantitative computed tomography (QCT) is a medical imaging technique that converts CT measurements into calibrated bone density values in mg/cm³, used to diagnose and monitor osteoporosis and enable opportunistic screening.

Quantitative coronary angiography

Quantitative coronary angiography (QCA) is an image-analysis method that measures coronary artery dimensions and stenosis severity from X-ray angiograms, and is the standard objective measure used in core laboratories and for stent sizing.

Quantitative CT

Quantitative CT (QCT) is a set of computational methods that extract numerical measurements, chiefly volumetric bone mineral density, from CT images rather than visual reading.

Quantitative electroencephalography

Quantitative electroencephalography (qEEG) is the mathematical processing of digitally recorded EEG, using spectral analysis and normative comparison to supplement, never replace, visual reading by a trained electroencephalographer.

Quantitative insulin sensitivity check index

The quantitative insulin sensitivity check index (QUICKI) is a fasting index, described in 2000, that estimates insulin sensitivity from fasting insulin and glucose for research use.

Quantitative light-induced fluorescence

Quantitative light-induced fluorescence (QLF) is a non-invasive dental diagnostic method that uses blue light to make tooth tissue fluoresce, quantifying demineralization to detect and monitor early caries lesions.

Quantitative magnetic resonance imaging

Quantitative magnetic resonance imaging (qMRI) is a family of MRI techniques that measure tissue properties such as relaxation times and diffusion as numerical values in physical units.

Quantitative sensory testing

Quantitative sensory testing (QST) is a standardized, non-invasive psychophysical method measuring detection and pain thresholds for thermal, mechanical, and vibratory stimuli to assess sensory nerve function.

Quantitative susceptibility mapping

Quantitative susceptibility mapping (QSM) is an MRI post-processing technique that converts gradient-echo phase images into maps of tissue magnetic susceptibility, quantifying iron, hemorrhage, and calcification.

Quantitative systems pharmacology

Quantitative systems pharmacology (QSP) is a modeling approach coupling mechanistic models of biological systems to pharmacokinetic and pharmacodynamic data to predict drug behavior, optimize dosing, and inform regulatory decisions.

Quantitative ultrasound

Quantitative ultrasound (QUS) analyzes raw ultrasound echo signals to measure attenuation, backscatter, and speed of sound, quantifying tissue properties for bone, liver fat, and breast cancer assessment.

QUANTRANS trial

QUANTRANS (NCT05798286) was a French multicenter randomized trial testing Quantra viscoelastic test-guided transfusion versus standard coagulation tests in double-lung transplantation; 128 patients, no reduction in transfusion (p = 0.923).

Quarantine

Quarantine (quaranta giorni, forty days) separates exposed but not-yet-ill people to prevent disease spread; first formalized in Ragusa 1377 and Venice 1348, with lazarettos from 1423, distinct from isolation of the sick.

Oct 20, 2026

Quavonlimab

Quavonlimab (MK-1308) is Merck's investigational humanized IgG1 anti-CTLA-4 monoclonal antibody, tested with pembrolizumab (coformulation MK-1308A) in lung cancer, melanoma, renal cell and colorectal cancer trials.

Quazepam

Quazepam (Doral) is a long-acting Schedule IV benzodiazepine hypnotic for insomnia, US-approved 1985 and relaunched 2016; half-life 27-41 hours, α1-GABA-A selective, dosed 7.5-15 mg.

Quebec platelet disorder

Quebec platelet disorder (QPD, factor V Quebec) is a rare autosomal dominant bleeding disorder from a 78-kb PLAU duplication causing >100-fold megakaryocyte uPA overexpression, delayed-onset bleeding, and response only to fibrinolytic inhibitors.

Queen Mary Hospital

Queen Mary Hospital (瑪麗醫院), Hong Kong public acute regional hospital at Pok Fu Lam, opened 1937, HKU teaching hospital, designated liver transplant centre since 2003, only multi-organ transplant hospital, undergoing HK$13.5 billion redevelopment.

Queensland Health

Queensland Health is Queensland's public health system: the Department of Health plus 16 Hospital and Health Services under the Hospital and Health Boards Act 2011, with a $33.1 billion 2025-26 budget, 119,438 FTE staff, and the $18.53 billion Hospital Rescue Plan.