Uncertainty contribution at NIS phototherapy irradiance facility

Alaa-Eldin A Abd-Elmageed, Sameh M Reda

(Photometry and Radiometry division, National Institute for Standards (NIS), Giza 12211-136, Egypt)

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Uncertainty contribution at NIS phototherapy irradiance facility

Alaa-Eldin A Abd-Elmageed, Sameh M Reda

(PhotometryandRadiometrydivision,NationalInstituteforStandards(NIS),Giza12211-136,Egypt)

Phototherapy lamps are the most effective and safest in the treatment of several medical treatments such as bilirubin. They transfer radiant energy expressed by irradiance unit in W/m2into the skin specifically to achieve a therapeutic reduction in the bilirubin concentration in the blood. National Institute for Standards (NIS) in Egypt builds up a radiometric method to ensure the competence of phototherapy sources (luminaire) to the standard international and national requirements. Hence, NIS provides traceability to customer through unbroken chain of phototherapy radiometer calibrated as irradiance response in W/m2. Uncertainty model including all parameters accompanied with the measurements is studied.

irradiance; jaundice treatment; phototherapy luminaire; uncertainty

Jaundice occurs in most newborn infants. Most jaundice is benign, but because of the potential toxicity of bilirubin, newborn infants must be monitored to identify those who might develop severe hyperbilirubinemia[1]. The most common therapeutic intervention used for the treatment of hyperbilirubinemia is phototherapy. It has become a mainstay since its introduction in 1958[2]. The effectiveness of neonatal hyperbilirubinaemia treatment depends directly on the amount of energy emitted by light expressed by spectral irradiance in W/m2/nm which defines as the power per unit area per wavelength[3]. The aim of phototherapy is to decrease the level of unconjugated bilirubin in order to prevent acute bilirubin encephalopathy hearing loss and kernicterus[4].

There are several methods of delivering phototherapy, all of which administer different dosages of spectral irradiance to the infant. According to standards requirements, normal phototherapy level is 8-10 μW/cm2/nm and intensive phototherapy level is greater than 30 μW/cm2/nm[1]. Luminaries under test must comply with the previous standard implementation and rationale phototherapy levels. For phototherapy to be effective photons of light from the lamp must be absorbed by the bilirubin molecule. Bilirubin appears yellow because it absorbs strongly blue and green light. Blue light around 450 nm is absorbed most readily if bilirubin is in a test tube. In a baby, other factors, including skin penetration and albumin binding, combine to cause a color shift of the most effective light toward the blue-green region[4-5].

1 Materials and methods

A setup is used to evaluate the irradiance levels produced from a phototherapy luminaire to ensure its competence to fulfill the requirements of the international standards[6]. It is based on measuring the irradiance levels of a luminaire at distance of 50 cm at different irradiated points using a standard calibrated radiometer model 268BLUE from the United Detector Technology (UDT) Inc. According to the requirement of the stranded, the irradiated area is a rectangle sheet, and its dimension is defined as 30 cm×60 cm[7-8].

The irradiance levels are measured at different points spreading over the irradiated area each separated by not more than 10 cm. Therefore, the irradiated area was divided into 3 rows and 5 columns, and there are 15 measured points, as shown in Fig.1. The irradiance levels have been measured for five times at the center of each of the above mentioned area cells, as shown in Fig.2.

Fig.1 Template for irradiance measurement sheet of phototherapy fluorescent luminaire equipment

Fig.2 A setup used for calibrating a phototherapy luminaire

In addition, intermediate checks can know the right time to replace the light sources. Keeping in mind that complete evaluation at each replacement is needed in order to maintain quality of the service and also raise the economic value of the phototherapeutic unit.

2 Results and discussion

Absolute total irradiance for Bilirubin (Ebi) in the range between 400 nm and 550 nm in W/m2is given by

whereE(λ) is the measured irradiance at an individual wavelength,λ, in W/m2/nm.

Evaluation of the uncertainty is done by the guide to the expression of uncertainty in measurement (GUM) method. This method is adopted and described in details by International Organization for Standardization (ISO)[9-10]. The standard uncertaintyu(xi) to be associated with input quantityxiis the estimated standard deviation of the mean[10].

The combined standard uncertaintyuc(y) is obtained by combining the individual standard uncertaintiesui, which can be evaluatede as Type A and Type B, that is,

For the determination of the phototherapy irradiance, the following evaluation model is used at the mean total irradianceEm=657 μW/cm2.

Uncertainty model used is

Em=Es+δEl+δEd+δEr+δEt+δEres.

Thesymbolmeansingsareasfollows:

1)Uncertaintyduetoreferencestandard.

Thecalibrationcertificateforthereferencestandardgivesavalueofirradianceresponsivitythatisequalto4.6×10-2A/W/cm2(at450nm)withanassociatedexpandeduncertaintyof1.68% (k=2).

2) Distance effect on the irradiance measurements between the phototherapy irradiated source and the effective surface area.

It is calculated by using the inverse square law as

3) Drift of the standard.

The drift of irradiance of the reference standard is estimated from annual calibrations to be zero, as it is a new detector, with estimated rectangle distribution of ±1 μW/cm2(k=2) at 657 μW/cm2.

4) Repatibility.

Standard deviation of the mean of repeates 5 times.

5) Temperature correction.

The temperature of the cabinet is monitored with a calibrated thermometer to be 24 ℃. Deviations from this value have been estimated to be within ± 1 ℃, thus the irradiance variation due to a temperature variation is estimated to be within ± 1 μW/cm2(k=2).

6) Resoultion of the reference phototherapy radiometer.

The expanded uncertainty of ± 0.000 1 μW/cm2(k=2) is assigned to the irradiance meter readings at the irradiance level of 657 μW/cm2.

Table 1 shows the uncertainty components accompanied with the phototherapy irradiance measurement. The uncertainty contribution in the irradiance measurement is calculated by the GUM method using the GUM workbench software[11], and equal to 1.7% atk=2, as shown in Fig.3.

Fig.3 Phototherapy irradiance uncertainty calculation using GUM workbench software program

Table 1 Uncertainty accompanied with phototherapy irradiance measurement

The uniformityGof the total irradiance for bilirubin defined as the ratio of the lowest irradiance levelEbi(min)to the highest irradiance levelEbi(max)on the effective surface area is given by

According to the standard requirement[7-8], the ratio ofEbi(min)toEbi(max)shall be greater than 0.4.Gcalculated in this measurement is equal to 0.6.

3 Conclusion

A radiometric method to ensure the competence of phototherapy sources (luminaire) to the standard international and national requirements is built up at NIS. Thus, NIS provides traceability to customer through unbroken chain of phototherapy radiometer calibrated as irradiance response in W/m2.

Uncertainty model including all parameters accompanied with the measurements is studied. Performance evaluation of phototherapy device depends on accurate measurements of the irradiance levels and its distribution over the irradiated surface using calibrated phototherapy radiometer. Selection of the standard device to perform the required medical service basically depends on good evaluation of the available phototherapy devices.

Although performance evaluation leads to improvement of the quality of treatment, it can provide accurate doses. Periodical measurements of the irradiance levels give serious information of the phototherapy performance and its possibility to serve its continuity in the provision of medical service required. The accompanied uncertainty with measurement is equal to 1.7%.

[1] American Academy of Pediatrics. Management of hyperbilirubinemia in the newborn infant 35 or more weeks of gestation. Pediatrics, 2004, 114(1): 297-316.

[2] Facchini F P. Standardizing the calibration of phototherapy devices-a proposal. Jornal de Pediatria, 2001, 77(2): 67-74.

[3] Ferreira A L C, Nascimento R M, Veríssimo R C S S. Irradiance of phototherapy equipment in maternity wards in Maceió. Revista de Latino-Americana de Enfermagem, 2009, 17(5): 695-700.

[4] Van den Belt V W, Van der Heide M, Van Imhoff D E, et al. Irradiance levels of phototherapy in jaundiced preterm infants. Archives of Disease in Childhood, 2008: 93.

[5] Wentworth D P. Neonatal phototherapy-today’s lights, lamps and devices. Infant, 2005, 1(1): 14-19.

[6] Reda S M, Abd Elbaset Y. Performance evaluation for hyperbilirubinemia phototherapy equipment. Australian Journal of Basic and Applied Sciences, 2013, 7(9): 364-366.

[7] International Electrotechnical Commission (IEC). Particular requirements for the safety of infant phototherapy equipment. IEC 60601-2-50, 2000.

[8] Egyptian Organization for Standardization and Quality (EOS). Particular requirements for the safety of the infant Phototherapy equipment. ES 5807. 2007.

[9] ISO. Guide to the expression of uncertainty in measurement (GUM). International Organization for Standardization, 2008: 98-100.

[10] United Kingdom Accreditation Service (UKAS). The expression of uncertainty and confidence in measurement. 3rd edition. 2013.

[11] Metrodata GmbH. GUM Workbench edu software version 2.4.1.384.[2014-05-12]. http:∥www.metrodata.de/.

國家標(biāo)準(zhǔn)研究所光線療法輻照設(shè)備的不確定度分配

Alaa-Eldin A Abd-Elmageed, Sameh M Reda

(Photometry and Radiometry division, National Institute for Standards (NIS), Giza 12211-136, Egypt)

光療燈在治療諸如膽紅素等疾病中是最有效和最安全的。 光療燈能把每瓦特/平方米輻照單位的輻射能轉(zhuǎn)移到皮膚中， 降低血液中的膽紅素濃度。 埃及國家標(biāo)準(zhǔn)研究所(NIS)設(shè)立了輻射度測量標(biāo)準(zhǔn)， 確保光療源(泛光燈)達到國際標(biāo)準(zhǔn)和國家要求。 為此， 通過將一個光療輻射計的完整鏈作為每瓦特/平方米的輻射響應(yīng)， 國家標(biāo)準(zhǔn)研究向顧客提供可追蹤性， 對包含所有測量參數(shù)的不確定模型據(jù)進行了研究。

輻照； 黃疸病治療； 光療法光源； 不確定性

Alaa-Eldin A Abd-Elmageed, Sameh M Reda. Uncertainty contribution at NIS phototherapy irradiance facility. Journal of Measurement Science and Instrumentation, 2015, 6(4)： 332-335.

10.3969/j.issn.1674-8042.2015.04.005

Alaa-Eldin A. Abd-Elmageed (alaa_nis@yahoo.com)

1674-8042(2015)04-0332-04 doi： 10.3969/j.issn.1674-8042.2015.04.005

Received date： 2015-09-02

CLD number： R-33 Document code： A