Материал: part17

T.4.2 Interpolated Reference​

The interpolated reference obstruction analysis calculates a reconstruction diameter for each position in the analyzed artery. This​ reconstructed diameter represents the diameters of the artery when no disease would be present. The reconstruction diameter is a​ line fitted through at least two user-defined reference markers by linear interpolation.​

By default two references are used at the positions of the reference markers are automatically positioned at 5% and 95% of the artery​ length.​

To calculate a percentage diameter stenosis the reference diameter for the obstruction is defined as the reconstructed diameter at​ the position of the MLD.​

In cases where the proximal and distal part of the analyzed artery have a stable diameter during the treatment and long-term follow-​ up, this method will produce a stable reference diameter for all positions in the artery.​

T.4.3 Mean Local Reference​

In case of mean local reference obstruction the reference diameter will be an average of the diameters at the position of one or more​ the reference markers.​

This method is particularly appropriate for the analysis of bifurcated arteries.​

T.5 Positions in Diameter Graphic​

A vessel segment length as seen in the image is not always indicated as the same X-axis difference in the graph.​

The X-axis of the graph is based on pixel positions on the midline and these points are not necessarily equidistant. This is caused by​ the fact that vessels do not only run perfectly horizontally or vertically, but also at angles.​

When a vessel midline is covering a number of pixel positions perfectly horizontal or vertical, it will cover less space in mm compared​ to a vessel that covers the same number of pixel positions under an angle. When a segment runs perfectly horizontal or vertical, the​ segment length is equal to the amount of midline pixel points times the pixel separation (each point of the midline is separated exactly​ the pixel spacing in mm) and the points on the X-axis also represent exactly one pixel space. This is not the case when the vessel​ runs under an angle. For example an artery that is positioned at a 45 angle, the distance between two points on the midline is 0.7​ times the pixel spacing.​

As example, the artery consists of 10 elements (n =10); each has a length of 1mm (pixel size). If the MLD was exactly in the center​ of the artery you would expect the length from 0 to the MLD would be 5 sub segments long, thus 5 mm. This is true if the artery runs​ horizontal or vertically (assumed aspect ratio is 1).​

pixel elements

MLD

Figure T.5-1. Artery Horizontal​

If the artery is positioned in a 45º angle then the length of each element is √2 times the pixel size compared to the previous example.​ Thus the length depends on the angle of the artery.​

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pixel elements

artery

Figure T.5-2. Artery 45º Angle​

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U Ophthalmology Use Cases (Informative)​

U.1 Ophthalmic Photography Use Cases​

The following use cases are examples of how the DICOM Ophthalmology Photography objects may be used. These use cases utilize​ the term "picture" or "pictures" to avoid using the DICOM terminology of frame, instance or image. In the use cases, the series means​ DICOM Series.​

U.1.1 Routine N-spot Exam​

An N-spot retinal photography exam means that "N" predefined locations on the retina are examined.​

AroutineN-spotretinalphotographyexamisorderedforbotheyes.Thereisnothingunusualobservedduringtheexam,soNpictures​ are taken of each retina. This healthcare facility also specifies that in an N-spot exam a routine external picture is captured of both​ eyes, that the current intraocular pressure (IOP) is measured, and that the current refractive state is measured.​

The resulting study contains:​

a.​2N pictures of the retina and one external picture. Each retinal picture is labeled in the acquisition information to indicate its pos-​ ition in the local N-spot definition. The series is not labeled, each picture is labeled OS or OD as appropriate.​

Note​

DICOMusesL,R,andBintheImageLateralityAttribute(0020,0062).TheactualencodingswillbeL,R,orB.Ophthalmic​ equipment can convert this to OS, OD, and OU before display.​

b.​In the acquisition information of every picture, the IOP and refractive state information is replicated.​

c.​Since there are no stereo pictures taken, there is no Stereometric Relationship IOD instance created.​

The pictures may or may not be in the same Series.​

U.1.2 Routine N-spot Exam With Exceptions​

A routine N-spot retinal photography exam is ordered for both eyes. During the exam a lesion is observed in the right eye. The lesion​ spans several spots, so an additional wide angle view is taken that captures the complete lesion. Additional narrow angle views of​ the lesion are captured in stereo. After completing the N-spot exam, several slit lamp pictures are taken to further detail the lesion​ outline.​

The resulting study contains:​

a.​2N pictures of the retina and one external picture, one additional wide angle picture of the abnormal retina, 2M additional pictures​ for the stereo detail of the abnormal retina, and several slit lamp pictures of the abnormal eye. The different lenses and lighting​ parameters are documented in the acquisition information for each picture.​

b.​One instance of a Stereometric Relationship IOD, indicating which of the stereo detail pictures above should be used as stereo​ pairs.​

The pictures may or may not be in the same Series.​

U.1.3 Routine Flourescein Exam​

A routine fluorescein exam is ordered for one eye. The procedure includes:​

a.​Routine stereo N-spot pictures of both eyes, routine external picture, and current IOP.​

b.​Reference stereo picture of each eye using filtered lighting​

c.​Fluorescein injection​

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d.​Capture of 20 stereo pairs with about 0.7 seconds between pictures in a pair and 3-5 seconds between pairs.​

e.​Stereo pair capture of each eye at increasing intervals for the next 10 minutes, taking a total of 8 pairs for each eye.​

The result is a study with:​

a.​The usual 2N+1 pictures from the N-spot exam​

b.​Four pictures taken with filtered lighting (documented in acquisition information) that constitute a stereo pair for each eye.​

c.​40 pictures (20 pairs) for one eye of near term fluorescein. These include the acquisition information, lighting context, and time​ stamp.​

d.​32pictures(8pairsforeacheye)oflongtermfluorescein.Theseincludeacquisitioninformation,lightingcontext,andtimestamp.​

e.​One Stereometric Relationship IOD, indicating which of the above OP instances should be used as stereo pairs.​

The pictures of a) through d) may or may not be in the same series.​

U.1.4 External Examination​

The patient presents with a generic eye complaint. Visual examination reveals a possible abrasion. The general appearance of the​ eyes is documented with a wide angle shot, followed by several detailed pictures of the ocular surface. A topical stain is applied to​ reveal details of the surface lesion, followed by several additional pictures. Due to the nature of the examination, no basic ophthalmic​ measurements were taken.​

The result is a study with one or more series that contains:​

a.​One overall external picture of both eyes​

b.​Several close-up pictures of the injured eye​

c.​Several close-up pictures of the injured eye after topical stain. These pictures have the additional stain information conveyed in​ the acquisition information for these pictures.​

U.1.5 External Examination With Intention​

The patient is suspected of a nervous system injury. A series of external pictures are taken with the patient given instructions to follow​ a light with his eyes. For each picture the location of the light is indicated by the patient intent information, (e.g., above, below, patient​ left, patient right).​

The result is a study with one or more series that contains:​

a.​Individual pictures with each picture using the patient intent field to indicate the intended direction.​

U.1.6 External Examination With Drug Application​

Patient is suspected of myaesthenia gravis. Both eyes are imaged in normal situation. Then after Tensilon® (edrophonium chloride)​ injection a series of pictures is taken. The time, amount, and method of Tensilon® (edrophonium chloride) administration is captured​ in the acquisition information. The time stamps of the pictures are used in conjunction with the behavior of the eyelids to assess the​ state of the disease.​

Note​

Tensilon® is a registered trademark of Roche Laboratories.​

The result is a study with one or more series that contains:​

a.​Multiple reference pictures prior to test​

b.​Pictures with acquisition information to document drug administration time.​

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