New Hampshire Code of Administrative Rules
He - Department of Health and Human Services
Subtitle He-P - Former Division of Public Health Services
Chapter He-P 4000 - NEW HAMPSHIRE RULES FOR THE CONTROL OF RADIATION
Part He-P 4041 - USE OF RADIATION MACHINES: DEFINITIONS
Section He-P 4041.02 - Definitions

(a) "Accessible surface" means the external surface of the enclosure or housing of the radiation-producing machine as provided by the manufacturer.

(b) "Accessory component" means a component which is:

(c) "Added filtration" means any filtration which is in addition to the inherent filtration.

(d) "Air kerma (K) " means the kinetic energy released in air by ionizing radiation, and is determined as the quotient of dE by dM, where dE is the sum of the initial kinetic energies of all the charged ionizing particles liberated by uncharged ionizing particles in air of mass dM, and is expressed in the SI unit of joule per kilogram, and the special name the "gray" (Gy) .

(e) "Air kerma rate (AKR) " means the air kerma per unit time.

(f) "Aluminum equivalent" means the thickness of type 1100 aluminum alloy for which the nominal chemical composition is 99.00 percent minimum aluminum, 0.12 percent copper which affords the same attenuation, under specified conditions, as the material in question.

(g) "Annual" means a period of time or an event happening once a year.

(h) "Articulated joint" means a joint between 2 separate sections of a tabletop which provides the capacity of one of the sections to pivot on the line segment along which the sections join.

(i) "Assembler" means any person engaged in the business of assembling, replacing, or installing one or more components into an x-ray system or subsystem and includes the owner of an x-ray system or his or her employee or agent who assembles components into an x-ray system that is subsequently used to provide professional or commercial services.

(j) "Attenuation" means the reduction of exposure rate upon passage of radiation through matter.

(k) "Attenuation block" means a block or stack, having dimensions 20 centimeters by 20 centimeters by 3.8 centimeters, of type 1100 aluminum alloy or other materials having equivalent attenuation.

(l) "Automatic exposure control (AEC) " means a device which automatically controls one or more technique factors in order to obtain at a pre-selected location(s) a required quantity of radiation. The term includes devices such as phototimers and ion chambers.

(m) "Automatic exposure rate control (AERC) " means a device which automatically controls one or more technique factors in order to obtain at a pre-selected location(s) a required quantity of radiation.

(n) "Backscatter" means the scattering of radiation or particles in a direction opposite to that of the incident radiation due to reflection from particles of the medium traversed.

(o) "Backscatter system" means a security screening system that makes use of radiation scattered or deflected from an object or person to form an image of the scattering object or person.

(p) "Beam axis" means a line from the source through the center of the x-ray field.

(q) "Beam-limiting device" means a device which provides a means to restrict the dimensions of the x-ray field.

(r) "Beam monitoring system" means a system designed to detect and measure the radiation present in the useful beam.

(s) "Bone densitometry system" means a medical device which uses electronically-produced ionizing radiation to determine the density of bone structures of human patients.

(t) "Calibration" means:

(u) "C-arm Fluoroscope" means a fluoroscopic x-ray system in which the image receptor and x-ray tube housing assembly are connected or coordinated to maintain a spatial relationship. A C-arm fluoroscope system allows a change in the direction of the beam axis with respect to the patient without moving the patient.

(v) "Cantilevered tabletop" means a tabletop designed such that the unsupported portion can be extended at least 100 centimeters (cm) beyond the support.

(w) "Cassette holder" means a device, other than a spot film device, that supports and/or fixes the position of an image receptor during a radiographic exposure.

(x) "Cephalometric device" means a device intended for the radiographic visualization and measurement of the dimensions of the human head.

(y) "Certified components" mean components of x-ray systems which are subject to regulations promulgated under Public Law 90-602, the Radiation Control for Health and Safety Act of 1968.

(z) "Certified system" means any x-ray system which has one or more certified component(s) .

(aa) "Changeable filters" mean any filter, exclusive of inherent filtration, which can be removed from the useful beam through any electronic, mechanical, or physical process.

(ab) "Coefficient of variation" or "C" means the ratio of the standard deviation to the mean value of a population of observations. It is estimated using the following equation:

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where:

s = Standard deviation of the population;

x-bar = Mean value of observations in sample;

xi= The ith observation in sample; and

n = Number of observations in sample.

(ac) "Computed radiography (CR) " means a projection x-ray imaging method in which a cassette houses a phosphor plate rather than photographic film. This photostimulable phosphor-coated plate captures a latent image when exposed to x-rays and, when processed, releases light that is converted to a digital image.

(ad) "Computed tomography (CT) " means the production of a tomogram by the acquisition and computer processing of x-ray transmission data.

(ae) "Computed tomography dose index (CTDI) " means the integral from -7T to +7T of the dose profile along a line perpendicular to the tomographic plane divided by the product of the nominal tomographic section thickness and the number of tomograms produced in a single scan, that is:

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where:

z = Position along a line perpendicular to the tomographic plane;

D(z) = Dose at position z;

T = Nominal tomographic section thickness; and

n = Number of tomograms produced in a single scan.

This definition assumes that the dose profile is centered around z = 0 and that, for a multiple tomogram system, the scan increment between adjacent scans is nT.

(af) "Cone beam computed tomography (CBCT) " means a digital volume tomography method used in some imaging applications using two dimensional digital detector arrays, and a cone-shaped x-ray beam, instead of a fan-shaped beam, that rotates around the patient to generate a high resolution, 3D image, with high geometric accuracy. Reconstruction algorithms can be used to generate images of any desired plane.

(ag) "Contact therapy system" means an x-ray system used for therapy with the x-ray tube port placed in contact with or within 5 centimeters of the surface being treated.

(ah) "Contrast resolution" means the ability to detect, image and display similar tissues or materials such as gray-white matter and liver-spleen.

(ai) "Contrast scale (CS) " means the change in the linear attenuation coefficient per CTN relative to water, that is:

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where:

µx = Linear attenuation coefficient of the material of interest;

µ w = Linear attenuation coefficient of water;

CTNx= CTN of the material of interest; and

CTNw= CTN of water.

(aj) "Control panel" means that part of the x-ray control upon which are mounted the switches, knobs, pushbuttons, and other hardware necessary for manually setting the technique factors.

(ak) "Cooling curve" means the graphical relationship between heat units stored and cooling time.

(al) "CT conditions of operation" means all selectable parameters governing the operation of a CT x-ray system including, but not limited to, nominal tomographic section thickness, filtration, and the technique factors as defined in He-P 4041.02(cy) .

(am) "CT dosimetry phantom" means the phantom used for determination of the dose delivered by a CT x-ray system.

(an) "CT gantry" means the tube housing assemblies, beam-limiting devices, detectors, and the supporting structures and frames which hold these components.

(ao) "CT number (CTN) " means the number used to represent the x-ray attenuation associated with each elemental area of the CT image.

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CTN

where:

k = A constant, a normal value of 1,000 when the Hounsfield scale of CTN is used;

µ x = Linear attenuation coefficient of the material of interest; and

µ w = Linear attenuation coefficient of water.

(ap) "CT scan" means the complete process of collecting x-ray transmission data for the production of a tomogram. This includes data collected simultaneously during a single scan for the production of one or more tomograms.

(aq) "CT scan increment" means the amount of relative displacement of the patient with respect to the CT system between successive scans measured along the direction of the displacement.

(ar) "CT scan time" means the time between the beginning and end of the x-ray transmission data accumulation for a CT scan.

(as) "Cumulative air kerma" means the total air kerma accrued from the beginning of an examination or procedure and includes all contributions from fluoroscopic and radiographic irradiation.

(at) "Dead-man switch" means a switch so constructed that a circuit closing contact can be maintained only by continuous pressure on the switch by the operator.

(au) "Demonstration" means a showing of the merits of a machine to a prospective customer.

(av) "Diagnostic imaging system" means an assemblage of components for the generation, emission, reception, transformation, storage and visual display of the resultant image.

(aw) "Diagnostic source assembly" means the tube housing assembly with a beam-limiting device attached.

(ax) "Diagnostic x-ray system" means an x-ray system designed for irradiation of any part of the human or animal body for the purpose of diagnosis or visualization.

(ay) "Diagnostic x-ray imaging system" means an assemblage of components for the generation, emission and reception of x-rays and the transformation, storage and visual display of the resultant x-ray image.

(az) "Digital radiography (DR) " means an x-ray imaging method or radiography which produces a digital rather than film projection image. The term includes both CR and DDR.

(ba) "Direct Digital Radiography (DDR") means an x-ray imaging method in which a digital sensor, rather than photographic film or phosphor plate, is used to capture an x-ray image. DDR is a cassette-less imaging method providing faster acquisition time than cassette-based CR, using an electronic sensor that converts x-rays to electronic signals, current or charge, when exposed to x-rays.

(bb) "Direct scattered radiation" means that scattered radiation which has been deviated in direction only by materials irradiated by the useful beam.

(bc) "Dose area product (DAP) " means the product of the air kerma and the area of the irradiated field and is measured in Gy-cm2, so it does not change with the distance from the x-ray tube. The term includes the term kerma-area product (KAP) .

(bd) "Dose profile" means the dose as a function of position along a line.

(be) "Elemental area" means the smallest area within a tomogram for which the x-ray attenuation properties of a body are depicted.

(bf) "Entrance exposure rate" means the exposure in air per unit time at the point where the center of the useful beam enters the patient.

(bg) "Entrance skin exposure (ESE) " means x-ray exposure of the skin, expressed in mR or air kerma (Gy) .

(bh) "Equipment" means "x-ray equipment" as defined in He-P 4041.02(fo) .

(bi) "Exposure rate" means the amount of ionization produced or incident per unit of time.

(bj) "Field emission equipment" means equipment which uses an x-ray tube in which electron emission from the cathode is due solely to the action of an electric field.

(bk) "Filter" means material placed in the useful beam to absorb preferentially selected radiations.

(bl) "Fluoroscopic air kerma display devices" means separate devices, subsystems or components that provide the display of AKR and cumulative air kerma. They include radiation detectors, if any, electronic and computer components, associated software and data displays.

(bm) "Fluoroscopic imaging assembly" means the image receptor(s), the image intensifier, the spot-film device, electrical interlocks, and structural material providing linkage between the image receptor and diagnostic source assembly as a subsystem in which x-ray photons produce a fluoroscopic image.

(bn) "Fluoroscopic irradiation time" means the cumulative duration during an examination or procedure of operator-applied continuous pressure to the device, enabling x-ray tube activation in any fluoroscopic mode of operation.

(bo) "Fluoroscopic procedure" means the production and display of serial x-ray images for the purpose of observing real-time motion of anatomical structures.

(bp) "Fluoroscopy" means a technique for generating x-ray images and presenting them simultaneously and continuously as visible images.

(bq) "Focal spot" means the actual focal spot area projected on the anode of the x-ray tube bombarded by the electrons accelerated from the cathode and from which the useful beam originates.

(br) "General purpose radiographic x-ray system" means any radiographic x-ray system which, by design, is not limited to radiographic examination of specific anatomical regions.

(bs) "Gonad shield" means a protective barrier for the testes or ovaries.

(bt) "Half-value layer (HVL) " means the thickness of specified material which attenuates the beam of radiation to an extent such that the exposure rate is reduced to one-half of its original value and for which the contribution of all scattered radiation, other than any which might be present initially in the beam concerned, is deemed to be excluded.

(bu) "Hand-held x-ray equipment" means x-ray equipment that is designed to be hand-held during operation.

(bv) "Healing arts screening" means the testing of human beings using x-ray machines for the detection or evaluation of health indications when such tests are not specifically and individually ordered by a licensed practitioner of the healing arts legally authorized to prescribe such x-ray tests for the purpose of diagnosis or treatment.

(bw) "Heat unit" means a unit of energy equal to the product of the peak kilovoltage, milliamperes, and seconds.

(bx) "Image intensifier" means a device, installed in its housing, which instantaneously converts an x-ray pattern into a corresponding light image of higher intensity.

(by) "Image quality" means the exactness of a 2-dimensional representation of the patient's anatomy on the radiographic image.

(bz) "Image receptor" means any device, such as a fluorescent screen or radiographic film, which transforms incident x-ray photons either into a visible image or into another form which can be made into a visible image by further transformations.

(ca) "Image receptor support" means, for mammographic systems, that part of the system designed to support the image receptor in a horizontal plane during mammography.

(cb) "Inherent filtration" means the filtration of the useful beam provided by the permanently installed components of the tube housing assembly.

(cc) "Interventional procedures" means procedures that utilize imaging for guidance. Imaging includes, but is not limited to, fluoroscopy and CT scan.

(cd) "Irradiation" means the exposure of matter to ionizing radiation.

(ce) "Isocenter" means the center of the smallest sphere through which the beam axis passes when the equipment moves through a full range of rotations about a common center.

(cf) "Kerma" means the quantity as defined by the International Commission on Radiation Units and Measurements. The kerma, K, is the quotient of dEtr by dm, where dEtr is the sum of the initial kinetic energies of the all charged particles liberated by the uncharged particles in mass dm of material; thus K=dEtr/dm in units of J/kg, where the special name for the unit of kerma is gray (Gy) . When the material is air, the quantity is referred to as "air kerma."

(cg) "Kilovolts peak (kVp) " means "peak tube potential" as defined in He-P 4041.02(de) .

(ch) "kV" means kilovolts, which is 1,000 volts.

(ci) "kWs" means kilowatt-second which is equivalent to 103 watt-second where 1 watt-second = kV x mA x second.

(cj) "Last image hold (LIH) radiograph" means an image obtained either by retaining one or more fluoroscopic images, which can be temporarily integrated, at the end of a fluoroscopic exposure or by initiating a separate and distinct radiographic exposure automatically and immediately in conjunction with termination of the fluoroscopic exposure.

(ck) "Lateral fluoroscope" means the x-ray tube and image receptor combination in a biplane system dedicated to the lateral projection. It consists of the lateral x-ray tube housing assembly and the lateral image receptor that are fixed in position relative to the table with the x-ray beam axis parallel to the plane of the table.

(cl) "Lead equivalent" means the thickness of lead affording the same attenuation, under specified conditions, as the material in question.

(cm) "Leakage radiation" means radiation emanating from the diagnostic or therapeutic source assembly other than the useful beam and radiation produced when the exposure switch or timer is not activated.

(cn) "Leakage technique factors" means the technique factors associated with the diagnostic or therapeutic x-ray source assembly which are used in measuring leakage and are defined as follows:

(co) "Lease" means a machine that is possessed and used for a specified term in exchange for consideration. The term includes "rental."

(cp) "Light field" means that area of the intersection of the light beam from the beam-limiting device and one of the set of planes parallel to and including the plane of the image receptor, whose perimeter is the locus of points at which the illumination is one-fourth of the maximum in the intersection.

(cq) "Line-voltage regulation" means the difference between the no-load and the load line potentials expressed as a percent of the load line potential calculated using the following equation:

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Percent line-voltage regulation =

where:

VN = No-load line potential; and

VL= Load line potential.

(cr) "Loaner" means a machine that is a replacement for a registered machine that is being repaired, calibrated or both. A loaner shall not include a machine that is purchased as a replacement for a registered machine.

(cs) "mA" means milliampere, which is 1/1,000 of an ampere.

(ct) "Magnetic resonance imaging scanner" means a diagnostic tool using a combination of magnetic fields and radio frequency waves to create cross-sectional images of the body.

(cu) "Magnetic resonance imaging (MRI) " means a non-invasive diagnostic procedure used to create cross-sectional images of the body by use of magnetic fields and radio frequency fields.

(cv) "Mammo-tomo" means breast tomosynthesis in which the x-ray tube moves in an arch during the exposure. The term includes "three dimensional breast imaging."

(cw) "mAs" means milliampere second, which is 1/1,000 of an ampere second.

(cx) "Maximum line current" means the root-mean-square current in the supply line of an x-ray machine operating at its maximum rating.

(cy) "Micro computed tomography" (Micro CT) means a scanning method that uses x-rays to create cross-sections of a physical object that can be used to recreate a virtual, 3-dimensional model. The pixel sizes of the cross-sections generated with this method are in the micrometer range. The term includes "high-resolution x-ray tomography."

(cz) "Mobile MRI unit" means a magnetic resonance imaging scanner that is approved by the federal Food and Drug Administration for the provision of diagnostic MRI services and which is physically located in a vehicle such as a self-contained van or tractor trailer for the purpose of transporting the magnetic resonance imaging scanner from one site to another.

(da) "Mobile x-ray equipment" means x-ray equipment mounted on a permanent base with wheels and/or casters for moving while completely assembled.

(db) "Multiple tomogram system" means a computed tomography x-ray system which obtains x-ray transmission data simultaneously during a single scan to produce more than one tomogram.

(dc) "Noise" means the standard deviation of the fluctuations in CTN expressed as a percentage of the attenuation coefficient of water and is calculated using the following equation:

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where:

CS= Contrast scale as defined in He-P 4041.02(t) ;

µw = Linear attenuation coefficient of water; and

s = Standard deviation of the CTN of picture elements in a specified area of the CT image.

(dd) "Nominal tomographic section thickness" means the full width at half-maximum of the sensitivity profile taken at the center of the cross-sectional volume over which x-ray transmission data are collected.

(de) "O-Arm" means a mobile fluoroscope, operated as a C-arm fluoroscope, which is opened and positioned over the area of interest on the patient being examined then closed around the patient to facilitate 360-degree x-ray imaging.

(df) "Patient" means an individual or animal subjected to healing arts examination, diagnosis, or treatment.

(dg) "Peak tube potential" means the maximum value of the potential difference across the x-ray tube during an exposure.

(dh) "Phantom" means a volume of material with an atomic number (Z) and density similar to biological tissue, which behaves in a manner similar to tissue with respect to the attenuation and scattering of radiation.

(di) "Physician assistant" means a person licensed as a physician assistant by the New Hampshire board of medicine.

(dj) "Phototimer" means a method for controlling radiation exposure to image receptors by the amount of radiation which reaches a radiation monitoring device(s) that is part of an electronic circuit which controls the duration of time the tube is activated.

(dk) "Picture element" means an elemental area of a tomogram.

(dl) "Portable x-ray equipment" means x-ray equipment designed to be hand carried.

(dm) "Position indicating device (PID) " means a device on dental x-ray equipment used to indicate the beam position and to establish a definite source-surface (skin) distance. It may or may not incorporate or serve as a beam-limiting device.

(dn) "Positive beam limitation (PBL) " means the automatic or semi-automatic adjustment of an x-ray beam to the size of the selected image receptor, whereby exposures cannot be made without such adjustment.

(do) "Primary protective barrier" means the material, excluding filters, placed in the useful beam, for protection purposes, to reduce the radiation exposure.

(dp) "Protective apron" means an apron made of radiation absorbing materials used to reduce radiation exposure.

(dq) "Protective barrier" means a barrier of radiation absorbing material(s) used to reduce radiation exposure.

(dr) "Protective glove" means a glove of radiation absorbing materials used to reduce radiation exposure.

(ds) "Pulsed mode" means operation of the x-ray system such that the x-ray tube current is pulsed by the x-ray control to produce one or more exposure intervals of duration less than one-half second.

(dt) "Quality assurance" means a program providing for verification by written procedures such as testing, auditing, and inspection to ensure that deficiencies, deviations, defective equipment, or unsafe practices, or a combination thereof, relating to the use, disposal, management or manufacture of radiation devices are identified, promptly corrected and reported to the appropriate regulatory authorities.

(du) "Qualified expert" means an individual who has demonstrated to the satisfaction of DHHS/RHS that such individual possesses the knowledge, skills and training to measure ionizing radiation to evaluate radiation parameters, to evaluate safety techniques and to advise regarding radiation protection needs as described in He-P 4040.

(dv) "Radiation detector" means a device which in the presence of radiation provides a signal or other indication suitable for use in measuring one or more quantities of incident radiation.

(dw) "Radiation therapy simulation system" means a radiographic or fluoroscopic x-ray system intended for localizing the volume to be exposed during radiation therapy and confirming the position and size of the therapeutic irradiation field.

(dx) "Radiograph" means an image receptor on which the image is created directly or indirectly by an x-ray pattern and results in a permanent record.

(dy) "Radiographic imaging system" means any system whereby a permanent or semi-permanent image is recorded on an image receptor by the action of ionizing radiation.

(dz) "Rated line voltage" means the range of potentials, in volts, of the supply line specified by the manufacturer at which the x-ray machine is designed to operate.

(ea) "Rated output current" means the maximum allowable load current of the x-ray high-voltage generator.

(eb) "Rating" means the operating limits as specified by the component manufacturer.

(ec) "Recording" means producing a permanent form of an image resulting from x-ray photons.

(ef) "Reference plane" means a plane which is displaced from and parallel to the tomographic plane.

(eg) "Resolution" means the ability to image two separate objects and visually distinguish one from the other.

(eh) "Response time" means the time required for an instrument system to reach 90 percent of its final reading when the radiation-sensitive volume of the instrument system is exposed to a step change in radiation flux from zero sufficient to provide a steady state mid-scale reading.

(ei) "Scan" means the complete process of collecting x-ray transmission data for the production of a tomogram which may be collected simultaneously during a single scan for the production of one or more tomograms.

(ej) "Scan increment" means the amount of relative displacement of the patient with respect to the CT x-ray system between successive scans measured along the direction of such displacement.

(ek) "Scan sequence" means a pre-selected set of two or more scans performed consecutively under pre-selected CT conditions of operation.

(el) "Scan time" means the period of time between the beginning and end of x-ray transmission data accumulation for a single scan.

(em) "Scattered radiation" means radiation that, during passage through matter, has been deviated in direction.

(en) "Secondary dose monitoring system" means a system that will terminate irradiation in the event of a failure of the primary system.

(eo) "Secondary protective barrier" means a barrier sufficient to attenuate the stray radiation to the required degree.

(ep) "Security screening system" means a non-medical use screening system designed for the detection of contraband and weapons concealed on a person or in a vehicle while being occupied by one or more people.

(eq) "Security screening system" means a non-medical use screening system designed for the detection of contraband and weapons concealed on a person or in a vehicle while being occupied by one or more people.

(er) "Shutter" means a device attached to the tube housing assembly which can intercept the entire cross-sectional area of the useful beam and which has a lead equivalency not less than that of the tube housing assembly.

(es) "Single tomogram system" means a CT x-ray system which obtains x-ray transmission data during a scan to produce a single tomogram.

(et) "Spatial frequency" means a measure of the changes in tissue attenuation characteristics. Abrupt changes have high spatial frequency (e.g., bone-lung interface), and gradual changes (e.g., liver-spleen interface) have low spatial frequency. Spatial frequency is expressed as line pair per millimeter (lp/mm) .

(eu) "Spatial resolution" means the ability to image anatomical structures or small objects that have high subject contrast, such as bone versus soft tissue.

(ev) "Solid state x-ray imaging device" means an assembly, typically in a rectangular panel configuration, that intercepts x-ray photons and converts the photon energy into a modulated electronic signature representative of the x-ray intensity over the area of the imaging device. The electronic signal is then used to create an image for display, storage or both.

(ew) "Source" means the focal spot of the x-ray tube.

(ex) "Source-image receptor distance (SID) " means the distance from the source to the center of the input surface of the image receptor.

(ey) "Source-skin distance (SSD) " means the distance from the source to the center of the entrant x-ray field in the plane tangent to the patient skin surface.

(ez) "Spot check" means an abbreviated calibration procedure which is performed to assure that a previous calibration continues to be valid.

(fa) "Spot film" means a radiograph which is made during a fluoroscopic examination to permanently record conditions which exist during that fluoroscopic procedure.

(fb) "Spot-film device" means a device intended to transport and/or position a radiographic image receptor between the x-ray source and fluoroscopic image receptor and includes a device intended to hold a cassette over the input end of an image intensifier for the purpose of making a radiograph.

(fc) "Stationary x-ray equipment" means x-ray equipment which is installed in a fixed location.

(fd) "Stray radiation" means the sum of leakage and scattered radiation.

(fe) "Supervising physician" means a physician who holds a current license issued by the New Hampshire board of medicine and who supervises all professional activities of a physician assistant.

(ff) "Technique factors" means the following conditions of operation:

(fg) "Tenth-value layer (TVL) " means the thickness of a specified material which attenuates x-radiation or gamma radiation to an extent such that the air kerma rate, exposure rate, or absorbed dose rate is reduced to one-tenth of the value measured without the material at the same point.

(fh) "Termination of irradiation" means the stopping of irradiation in a fashion which will not permit continuance of irradiation without the resetting of operating conditions at the control panel.

(fi) "Transmission system" means a security screening system using the conventional means of radiographic imaging in which x-rays pass through a target, such as a person or object and create shadow-grams of enclosed objects, such as contraband, based on their radiation attenuating properties.

(fj) "Tomogram" means the depiction of the x-ray attenuation properties of a section through the body.

(fk) "Tomographic plane" means that geometric plane which is identified as corresponding to the output tomogram.

(fl) "Tomographic section" means the volume of an object whose x-ray attenuation properties are imaged.

(fm) "Tube" means an x-ray tube, unless otherwise specified.

(fn) "Tube housing assembly" means the tube housing with tube installed to include the high-voltage and/or filament transformers and other appropriate elements when such are contained within the tube housing.

(fo) "Tube rating chart" means the set of curves which specify the rated limits of operation of the tube in terms of the technique factors.

(fp) "Useful beam" means the radiation emanating from the tube housing port or the radiation head and passing through the aperture of the beam limiting device when the exposure controls are in a mode to cause the system to produce radiation.

(fq) "Variable-aperture beam-limiting device" means a beam-limiting device which has capacity for stepless adjustment of the x-ray field size at a given SID.

(fr) "Visible area" means that portion of the input surface of the image receptor over which incident x-ray photons are producing a visible image.

(fs) "Wedge filter" means an added filter effecting continuous progressive attenuation on all or part of the useful beam.

(ft) "X-ray diffraction (XRD) " means the analysis of the characteristic atomic pattern of x-rays scattered when the primary beam from the machine strikes the sample.

(fu) "X-ray exposure control" means a device, switch, button or other similar means by which an operator initiates and/or terminates the radiation exposure and may include such associated equipment as timers and back-up timers.

(fv) "X-ray equipment" means an x-ray system, subsystem, or component thereof.

(fw) "X-ray field" means that area of the intersection of the useful beam and any one of the set of planes parallel to and including the plane of the image receptor, whose perimeter is the locus of points at which the exposure rate is one-fourth of the maximum in the intersection.

(fx) "X-ray fluorescence (XRF) " means the analysis of the characteristic x-rays created when the primary beam from the machine strikes the sample.

(fy) "X-ray high-voltage generator" means a device which transforms electrical energy from the potential supplied by the x-ray control to the tube operating potential and may include a means for transforming alternating current to direct current, filament transformers for the x-ray tube(s), high-voltage switches, electrical protective devices, and other appropriate elements.

(fz) "X-ray reciprocity" means any business entity proposing to bring a radiation machine into this state from another state for operation only by the business entity, except in areas of exclusive federal jurisdiction, for a period not in excess of 180 days in any calendar year.

(ga) "X-ray subsystem" means any combination of two or more components of an x-ray system for which there are requirements specified in this section.

(gb) "X-ray system" means an assemblage of components for the controlled production of x-rays and includes as a minimum an x-ray high-voltage generator, an x-ray control, a tube housing assembly, a beam-limiting device, and the necessary supporting structures and may include additional components which function with the system which are considered integral parts of the system.

(gc) "X-ray table" means a patient support device with its patient support structure or tabletop interposed between the patient and the image receptor during radiography or fluoroscopy and may include any stretcher equipped with a radiolucent panel or any table equipped with a cassette tray (bucky), cassette tunnel, image intensifier, or spot-film device beneath the tabletop.

(gd) "X-ray tube" means any electron tube which is designed to be used primarily for the production of x-rays.