Dr Gavakshi Gaur, Dr Priya Raj
ABSTRACT
Medical measurements play a crucial role in daily life, serving as key elements in the prevention, diagnosis, and treatment of diseases. As such, there is increasing interest in understanding the importance of metrological decisions and conformity assessments, particularly in contexts where measurements support health. This paper examines the use of medical devices with an emphasis on enhancing their metrological traceability. It highlights the specific role of metrology in healthcare and the impact of legal controls within the framework of medical device regulations involving measurement functions. A new regulatory approach is proposed for medical devices in use, addressing the convergence between European policy enforcement and metrological regulations.
Keywords: Metrology, Measurement, Weight
INTRODUCTION
Metrology, as defined by the International Bureau of Weights and Measures, is the science of measurement, encompassing both experimental and theoretical determinations across all levels of uncertainty in any area of science and technology.
Grasping metrological concepts and acknowledging their limitations and constraints is essential for interpreting clinical study results and evaluating new medical technologies. It is vital for physicians to share a common understanding of objectives, terminology, units, and measurement criteria with other scientists. This is especially important in anaesthesiology and intensive care medicine, where the growing number of medical devices plays a significant role in clinical decision-making.
Concept of Metrology is the science of weights and measures:
It involves the study of different systems of weights and measures, their interconnections, and an understanding of the mathematics that underlies them.
Weights
- Weight is the measurement of the gravitational force exerted on a specific object.
- It is directly related to the object’s mass: Weight = Mass × Gravitational Force.
- Factors like temperature, pressure, altitude, and latitude are usually ignored except when measuring weight with extreme precision. Measures
Measures
- Measures involve determining the volume or space that an object occupies.
- Temperature and pressure significantly influence measurements, especially in the case of gases and liquids.
Different systems: Various systems are utilized globally for measuring the weights and measures of drug substances. Among these, the Metric System stands out as the most widely recognized and accepted internationally.
- Metric system –
(a) It is internationally accepted decimal system of weights and measures—-( In U.K., U.S.A. the FPS System is legal).
(b) It is primarily used in continental Europe.
Advantages of this system include the division of units into tenths, a clear relationship between the units of volume and length, and the comparability of the unit of volume to the unit of weight.
Uses- For measuring solid substances.
- Imperial systems
The Imperial system of weights and measures, commonly referred to as the Avoirdupois system, was officially recognized by the British Pharmacopoeia. The term “Avoirdupois” comes from the French words “avoir” and “pois,” which mean “to have weight.”
- Apothecary’s System
(USA)Applied by the pharmacist before 1979, based on Troy ounce(T. oz.).
Quantities and Units In the field of metrology, understanding the concept of a quantity is fundamental. A quantity is essentially a measurable attribute of a phenomenon, object, or substance that can be expressed numerically along with a reference framework. This reference can include measurement units, procedures, or materials used to define and standardize the magnitude of the quantity.
Measurement
A measurement involves experimentally obtaining one or more values that can be reasonably associated with a specific quantity. The true value of this quantity is unique at any given moment but remains unknowable. As a result, measurement outcomes are typically presented as a single measured value along with an associated measurement uncertainty. The measurand refers to the quantity being measured. Measurement methods rely on principles, which are physical, chemical, or biological phenomena that serve as the foundation for the measurement. For instance, the thermoelectric effect is a method for measuring temperature, while infrared spectroscopy is used for determining HbO2 concentration. A reference measurement procedure is recognized for providing results suitable for their intended purpose. While not officially defined internationally, a “gold standard” is considered the best available reference method. The difference between a measurement and a reference value is distinguished by their different properties.
Measurement precision refers to how closely multiple measurements of the same quantity agree when taken under the same or similar conditions. It is associated with random measurement error and is typically quantified using metrics such as standard deviation (σ), variance (σ²), or coefficient of variation (σ/mean), assuming a mean of zero. The level of precision is often assessed based on confidence intervals (68%, 95%, or 99%) using 1σ, 2σ, or 3σ, respectively. Precision also defines measurement repeatability and reproducibility: repeatability refers to precision under consistent conditions (same procedure, operators, system, and location) over a short period, while reproducibility refers to precision across different conditions (locations, operators, systems) with repeated measurements.
Measurement error is the difference between a specific measured value and a reference value. It can be systematic (bias), affecting trueness, or random, affecting precision. When “measurement error” is mentioned without additional context, it generally refers to a combination of systematic and random errors, impacting overall inaccuracy. Accuracy pertains to a single measurement, while trueness and precision are derived from repeated measurements. Averaging measurement errors can be complex, as it’s important to use absolute values or their square roots to avoid cancelling out positive and negative errors, which could lead to confusion between accuracy and trueness. Understanding these differences is crucial, as they involve different error mechanisms and correction methods. Systematic errors usually point to issues in signal processing that can be addressed through improvements in sensing, amplification, calibration, or correction methods. Measurement uncertainty is a parameter that describes the range of possible values attributed to a measured based on available information. It encompasses more than just precision, including factors such as time drift, definitional uncertainty, and other sources of uncertainty. There are two types of uncertainty evaluation: Type A, which is based on statistical analysis of the measured values, and Type B, which relies on other sources like certified references, authoritative publications, or personal experience.
Devices for measurement Measuring devices are tools used to perform measurements either independently or as part of a system that includes additional devices. Often, a measuring instrument, or gauge, functions as a transducer, converting an input quantity (usually a physiological signal) into an output quantity (commonly an electric current) that has a specific relationship with the input. The physiological signal is captured by a sensor, which is a component of the measuring system directly influenced by the quantity being measured. Alternatively, a detector, which signals the presence of a phenomenon, body, or substance when an associated quantity exceeds a threshold, may also be used. Measurement Standards (Etalons)
Measurement standards (Etalons) are essential for any measurement process. They serve as the reference for defining a quantity, providing a specific value and associated measurement uncertainty. The uncertainty in these standards affects the overall measurement uncertainty because measurements are essentially ratios of the measured values to the standard, both expressed in the same units. For example, a weight of 80 kg means 80 times the value of a 1 kg standard with an uncertainty of ±3 µg. This review does not address the practical aspects of realizing measurement standards. For instance, the international standard for a meter is defined by the distance light travels in a vacuum in 1/299,792,458 of a second, with the second based on 9,192,631,770 periods of radiation from a cesium-133 atom.
CONCLUSIONS
A brief overview on the key role of Metrology and legal control in the filed of medical measurements, and also some suggestions for new approach focusing the present National and European regulatory system. Taking into account the technological innovation, economic significance and technical barrier, it was given an explanation about the legal framework of Member State and the consequent impact in the field of metrologicalregulates. It was also highlighted the actual situation inPortugal, where after placed in the market and put intoService no further regulated metrological control exists for the major of medical devices with measuring functions. Undoubtedly, this issue plays an important role in field ofMedicine measurements.
A basic understanding of metrology is essential for the daily practice of medicine. In intensive care, clinical decision-making is often determined by measurements of physiological and other variables to an extent unrivalled by most other medical specialties. Therapeutic success and ultimately outcomes in the critically ill depend on the correct interpretation of such measurements. Therefore, physicians should be aware of metrological concepts and understand the limitations and constraints. In addition, the interactions between medicine and other scientific disciplines mandate a common language. Since international consensus definitions exist, we must use them and promote them in the medical research and literature.
Acknowledgment
The author wishes to acknowledge Dr. Rajesh K. Meena, Associate Professor and Dr. Astha Mathur, Assistant Professor for their invaluable guidance and support.
BIBLIOGRAPHY
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- Bureau International des poiuds et Mesures; Joint Committee for Guides in Metrology. International Vocabulary of Metrology-Basic and General Concepts and Associated Terms (VIM).Paris: 2012.
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Gavakshi Gaur, Priya Raj
University College of Homoeopathy, Kekri
(Constituent College of Dr Sarvepalli Radhakrishnan Rajasthan Ayurved University, Jodhpur),
Old CHC Building, Ajmeri Gate, Kekri – 305404.
Email: gaurgavakshi@gmail.com, priyaraj02497@gmail.com
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