IEC 62985-2019 pdf download
IEC 62985-2019 pdf download.Methods for calculating size specific dose estimates (SSDE) for computed tomography.
4 Verification of method used to calculate Dw(z)
4.1 General
The purpose of Clause 4 is to provide a method to verify a MANUFACTURER’S IMPLEMENTED WATER EQUIVALENT DIAMETER AT LONGITUDINAL POSITION Z, DW IMp(Z), against the REFERENCE WATER EQUIVALENT DIAMETER AT LONGITUDINAL POSITION Z Dw REF(Z). This verification compares a set of DWIMp(z) values calculated for water PHANTOMS and an anthropomorphic PHANTOM to the corresponding set of DWREF(Z) values calculated for the same PHANTOMS.
4.2 Characteristics of the water PHANTOMS
Each PHANTOM’S structural material thickness shall be the minimum practicable and shall have a length of at least 10 cm:
• Small water PHANTOM
The small water PHANTOM shall be cylindrical and have an inner water diameter (d) of 14 cm < d < 20 cm.
• Large water PHANTOM
The larger water PHANTOM shall be cylindrical and have an inner water diameter (d) of 28 cm d 34 cm.
These PHANTOM specifications shall apply unless otherwise stated in the ACCOMPANYING DOCUMENTS, in order to accommodate minor variations from these specifications.
4.3 Characteristics of the anthropomorphic PHANTOM
The anthropomorphic PHANTOM shall be a representative of an average adult human from the top of the head to the bottom of the pelvis. It shall have a comprehensive set of simulated internal organs and bones designed to yield the CT NUMBERS of their anatomical counterparts. The PHANTOM shall include a minimum of simulated soft tissue, lung, and bone.
More than one anthropomorphic PHANTOM may be utilized if, as a set, they are representative of average adult head, chest, abdomen and pelvis regions. In addition, verification with a paediatric PHANTOM(S) may also be performed.
A description of the anthropomorphic PHANTOMS(S) used shall be provided in the
ACCOMPANYING DOCUMENTS.
NOTE If an end user is evaluating the accuracy of l)WIMp(Z) values, differences between DWIMP(z) and OWREF(z) that are larger than the allowed tolerances (410) can occur if different PHANTOMS are used compared to those used by the MANUFACTURER.
4.4 Generation of DWREF(Z) for the water PHANTOMS
Scans of each water PHANTOM shall be used to obtain the axial images for the calculation of Dw REF(Z), generated using 120 kV (or the closest available kV setting). The PHANTOMS shall be placed on the PATIENT SUPPORT (including pad) and positioned in a clinically relevant- manner without additional material in the scan field.
The CT CONDITIONS OF OPERATION and reconstruction parameters shall be suitable for
— a small water PHANTOM, and
— a large water PHANTOM.
Cardiac acquisitions, acquisitions without table movement, and shuttle mode acquisitions shall not be used. The use of AUTOMATIC EXPOSURE CONTROL shall correspond to its use in the clinical protocol selected. The reconstructed field of view shall be large enough to fully encompass the PHANTOMS.
The scan(s) shall be at least 5 cm in length and centred cross-sectionally and longitudinally on the PHANTOM. Contiguous Images of approximately 5 mm nominal reconstruction thickness shall be reconstructed.
The CT CONDITIONS OF OPERATION, scan positioning, and reconstruction parameters for the scanning of each PHANTOM shall be included in the ACCOMPANYING DOCUMENTS.
NOTE Image reconstruction kernels, such as those for edge enhancement, with a non-linear relationship between the CT NUMBER and the linear ATTENUATION coefficients can adversely affect the determination of
4.5 Verification of DWREF for the water PHANTOMS
DWREF(Z) shall be calculated at each longitudinal position z. The set of DWREF(Z) values shall be compared to the corresponding outer diameter of each water PHANTOM. The two values at each position shall agree to within 7 %, for each PHANTOM size.
4.6 GeneratIon of ‘w,IMp for the water PHANTOMS
DWIMP(z) shall be calculated at each of the z positions where D REF(Z) values were obtained.IEC 62985 pdf download.
