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Patient Dose Management
Patient Dose Management
Factors that influence Patient Absorbed Dose
Factors that influence Patient Absorbed Dose
Positioning of image receptor and X ray source relative to the patient
Positioning of image receptor and X ray source relative to the patient
Only a small percentage (typically ~1%) penetrate through to create
Only a small percentage (typically ~1%) penetrate through to create
Inverse Square Law
Inverse Square Law
Lecture 5: Patient Dose Management
Lecture 5: Patient Dose Management
Inverse Square Law (1)
Inverse Square Law (1)
Inverse Square Law (1)
Inverse Square Law (1)
Distance between patient and detector
Distance between patient and detector
Inverse Square Law (2)
Inverse Square Law (2)
Distance between patient and X ray source
Distance between patient and X ray source
Tall vs
Tall vs
Beam Orientation
Beam Orientation
ISOCENTER
ISOCENTER
ISOCENTER
ISOCENTER
Beam Orientation
Beam Orientation
Overlap Areas in Beam Re-orientation
Overlap Areas in Beam Re-orientation
Beam Orientation
Beam Orientation
Imaging modes  Fluoroscopy, (Cine) Acquisition, Digital Subtraction
Imaging modes Fluoroscopy, (Cine) Acquisition, Digital Subtraction
Fluoroscopy vs Cine Acquisition
Fluoroscopy vs Cine Acquisition
Patient Dose Management
Patient Dose Management
Can you tell
Can you tell
Image Quality
Image Quality
ALARA
ALARA
Siemens Axiom Artis, Fluoro low dose 20 cm PMMA 13
Siemens Axiom Artis, Fluoro low dose 20 cm PMMA 13
Lowest input dose needed to generate a USABLE image
Lowest input dose needed to generate a USABLE image
Duration of Fluoroscopy/Cine Acquisition
Duration of Fluoroscopy/Cine Acquisition
Digital Image Subtraction (DSA)
Digital Image Subtraction (DSA)
Pulsed Fluoroscopy
Pulsed Fluoroscopy
Pulsed Fluoroscopy
Pulsed Fluoroscopy
Each angiographic run consists of multiple still images taken in
Each angiographic run consists of multiple still images taken in
Continuous fluoroscopy
Continuous fluoroscopy
Lecture 5: Patient Dose Management
Lecture 5: Patient Dose Management
Pulsed Fluoroscopy
Pulsed Fluoroscopy
Pulsed Fluoroscopy
Pulsed Fluoroscopy
Lecture 5: Patient Dose Management
Lecture 5: Patient Dose Management
Lecture 5: Patient Dose Management
Lecture 5: Patient Dose Management
Lecture 5: Patient Dose Management
Lecture 5: Patient Dose Management
Variable Pulsed Fluoroscopy
Variable Pulsed Fluoroscopy
Collimation
Collimation
Collimation
Collimation
A word about collimation
A word about collimation
Collimation
Collimation
Scattered Radiation
Scattered Radiation
Scattered Radiation
Scattered Radiation
Collimation: Contrast Improvement by Reducing X ray Beam Size
Collimation: Contrast Improvement by Reducing X ray Beam Size
Beam Orientation, Overlap and Collimation
Beam Orientation, Overlap and Collimation
Collimation
Collimation
Factors that influence Patient Absorbed Dose
Factors that influence Patient Absorbed Dose
Lecture 5: Patient Dose Management
Lecture 5: Patient Dose Management
Lecture 5: Patient Dose Management
Lecture 5: Patient Dose Management
Field of View of Image Receptors
Field of View of Image Receptors
Equipment Selection
Equipment Selection
Dose rate dependence on image receptor active field-of-view or
Dose rate dependence on image receptor active field-of-view or
IMAGE INTENSIFIER
IMAGE INTENSIFIER
How input dose rate changes with different FOVs depends on machine
How input dose rate changes with different FOVs depends on machine
Beam Energy, Filter & kVp
Beam Energy, Filter & kVp
Image Contrast
Image Contrast
Effect of X ray Beam Penetration on Contrast, Body Penetration, and
Effect of X ray Beam Penetration on Contrast, Body Penetration, and
In general, every X ray system produces a range of energies
In general, every X ray system produces a range of energies
The goal is to shape the beam energy spectrum for the best contrast at
The goal is to shape the beam energy spectrum for the best contrast at
kVp (kiloVolt-peak)
kVp (kiloVolt-peak)
Comparison of Photon Energy Spectra Produced at Different kVp Values
Comparison of Photon Energy Spectra Produced at Different kVp Values
Filtration
Filtration
Filter
Filter
Filtration  possible disadvantage
Filtration possible disadvantage
Filtration potential disadvantage
Filtration potential disadvantage
Dose vs
Dose vs
Efficient Dose and Image Quality Management
Efficient Dose and Image Quality Management
Multiple Procedures
Multiple Procedures
Procedure Planning
Procedure Planning
Dose Fractionation in Interventional Cardiology
Dose Fractionation in Interventional Cardiology
Effect
Effect
Lab Personnel
Lab Personnel
Revision Qs: True or False
Revision Qs: True or False
Revision Qs: True or False
Revision Qs: True or False
Revision Qs: True or False
Revision Qs: True or False

: Patient Dose Management. : IAEA. : Patient Dose Management.ppt. zip-: 3563 .

Patient Dose Management

Patient Dose Management.ppt
1 Patient Dose Management

Patient Dose Management

L 5b

2 Factors that influence Patient Absorbed Dose

Factors that influence Patient Absorbed Dose

Procedural-related factors Positioning of image receptor and X ray source relative to the patient Beam orientation and movement Collimation Acquisition and fluoroscopic technique factors on some units Fluoroscopy pulse rate Acquisition frame rate Total fluoroscopy/acquisition time

Lecture 5: Patient Dose Management

2

3 Positioning of image receptor and X ray source relative to the patient

Positioning of image receptor and X ray source relative to the patient

4 Only a small percentage (typically ~1%) penetrate through to create

Only a small percentage (typically ~1%) penetrate through to create

the image.

Beam entering patient typically ~100x more intense than exit beam in average size patient

Lecture 5: Patient Dose Management

4

5 Inverse Square Law

Inverse Square Law

X ray intensity decreases rapidly with distance from source; conversely, intensity increases rapidly with closer distances to source.

8.8 cm

17.5 cm

35 cm

70 cm

1 unit of intensity

4 units of intensity

16 units of intensity

64 units of intensity

Lecture 5: Patient Dose Management

5

6 Lecture 5: Patient Dose Management

Lecture 5: Patient Dose Management

6

7 Inverse Square Law (1)

Inverse Square Law (1)

All other conditions unchanged, moving image receptor toward patient lowers radiation output rate and lowers skin dose rate.

Image Receptor

Image Receptor

4 units of intensity

Lecture 5: Patient Dose Management

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8 Inverse Square Law (1)

Inverse Square Law (1)

Lesson: Keep the image intensifier as close to the patient as is practicable for the procedure.

Image Receptor

Image Receptor

4 units of intensity

Lecture 5: Patient Dose Management

8

9 Distance between patient and detector

Distance between patient and detector

Lecture 5: Patient Dose Management

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10 Inverse Square Law (2)

Inverse Square Law (2)

All other conditions unchanged, moving patient toward or away from the X ray tube can significantly affect dose rate to the skin

Lesson: Keep the X ray tube at the practicable maximum distance from the patient.

Lecture 5: Patient Dose Management

10

11 Distance between patient and X ray source

Distance between patient and X ray source

Lecture 5: Patient Dose Management

11

12 Tall vs

Tall vs

Short Operators - Impact on Patient Dose?

Lecture 5: Patient Dose Management

12

13 Beam Orientation

Beam Orientation

14 ISOCENTER

ISOCENTER

Positioning anatomy of interest at the isocenter permits easy reorientation of the C-arm. This usually shortens the distance between the X ray tube and the patient, increasing the patients entrance port skin dose.

Lecture 5: Patient Dose Management

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15 ISOCENTER

ISOCENTER

When isocenter technique is employed, move the image intensifier as close to the patient as practicable to limit dose rate to the entrance skin surface.

Lecture 5: Patient Dose Management

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16 Beam Orientation

Beam Orientation

Physical factors and challenges to radiation management

Lesson: Reorienting the beam distributes dose to other skin sites and reduces risk to single skin site.

This is especially important in coronary angioplasty for chronic total occlusion.

Lecture 5: Patient Dose Management

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17 Overlap Areas in Beam Re-orientation

Overlap Areas in Beam Re-orientation

Lesson: Reorienting the beam in small increments may leave area of overlap in beam projections, resulting in large accumulations for overlap area (red area). Good collimation can reduce this effect.

Reproduced with permission from Wagner LK, Houston, TX 2004.

Lecture 5: Patient Dose Management

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18 Beam Orientation

Beam Orientation

Conclusion: Orientation of beam is usually determined and fixed by clinical need. When practical, reorientation of the beam to a new skin site can lessen risk to skin. Overlapping areas remaining after reorientation are still at high risk. Good collimation reduces the overlap area.

Physical factors and challenges to radiation management

Lecture 5: Patient Dose Management

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19 Imaging modes  Fluoroscopy, (Cine) Acquisition, Digital Subtraction

Imaging modes Fluoroscopy, (Cine) Acquisition, Digital Subtraction

Angiography

20 Fluoroscopy vs Cine Acquisition

Fluoroscopy vs Cine Acquisition

Influence of operation modes: from low fluoroscopy to cine, radiation / scatter dose rate could increase in a factor of 10-15

Lecture 5: Patient Dose Management

20

21 Patient Dose Management
22 Can you tell

Can you tell

Which image is FLUOROSCOPY ? Which one is ACQUISITION?

23 Image Quality

Image Quality

Radiation Dose

Better image quality with higher radiation dose reaching the image receptor. Tradeoff: higher patient dose!!

Lecture 5: Patient Dose Management

23

24 ALARA

ALARA

Physicians

Patients

Professional staff

As Low As Reasonably Achievable

No known safe limit of magnitude of radiation exposure.

Lecture 5: Patient Dose Management

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25 Siemens Axiom Artis, Fluoro low dose 20 cm PMMA 13

Siemens Axiom Artis, Fluoro low dose 20 cm PMMA 13

Gy/fr (entrance PMMA)

Siemens Axiom Artis Cine normal mode 20 cm PMMA 177 ?Gy/fr (entrance PMMA)

Lecture 5: Patient Dose Management

25

26 Lowest input dose needed to generate a USABLE image

Lowest input dose needed to generate a USABLE image

Set the default fluoroscopy mode to LOW

Lecture 5: Patient Dose Management

26

27 Duration of Fluoroscopy/Cine Acquisition

Duration of Fluoroscopy/Cine Acquisition

Important to keep in mind DURATION of fluoroscopy ? fluoroscopy x 10-15 sec ~ cine x 1 sec

Influence of operation modes: from low fluoroscopy to cine, radiation / scatter dose rate could increase in a factor of 10-15

Lecture 5: Patient Dose Management

27

28 Digital Image Subtraction (DSA)

Digital Image Subtraction (DSA)

Obtained by subtracting one image from another ? electronically removes information that is identical in 2 images Subtraction process accentuates image noise ? counter this effect by acquiring each of the original images at a substantially (up to 20x) higher dose per frame. Generally, studies that use DSA employ larger aggregate doses than do studies that employ unsubtracted cinefluorography.

Lecture 5: Patient Dose Management

28

29 Pulsed Fluoroscopy

Pulsed Fluoroscopy

30 Pulsed Fluoroscopy

Pulsed Fluoroscopy

Design of fluoroscopic equipment for proper radiation control

Understanding Variable Pulsed Fluoroscopy

Background: dynamic imaging captures many still images every second and displays these still-frame images in real-time succession to produce the perception of motion. How these images are captured and displayed can be manipulated to manage both dose rate to the patient and dynamic image quality. Standard imaging captures and displays 25 - 30 images per second.

Lecture 5: Patient Dose Management

30

31 Each angiographic run consists of multiple still images taken in

Each angiographic run consists of multiple still images taken in

quick succession.

[ video clip]

Lecture 5: Patient Dose Management

31

32 Continuous fluoroscopy

Continuous fluoroscopy

In conventional continuous-beam fluoroscopy there is an inherent blurred appearance of motion because the exposure time of each image lasts the full 1/30th of a second at 30 frames per second.

Continuous stream of X rays produces blurred images in each frame

Images

30 images in 1 second

X rays

Lecture 5: Patient Dose Management

32

33 Lecture 5: Patient Dose Management

Lecture 5: Patient Dose Management

33

34 Pulsed Fluoroscopy

Pulsed Fluoroscopy

Fluoroscopic pulsing X rays are produced during a small portion of the video frame time. The narrower the pulse width, the sharper the image. (? Faster shutter speed in camera )

Lecture 5: Patient Dose Management

34

35 Pulsed Fluoroscopy

Pulsed Fluoroscopy

Physical factors and challenges to radiation management

Pulsed imaging controls: Displaying 2530 picture frames per second is usually adequate for the transition from frame to frame to appear smooth. This is important for entertainment purposes, but not necessarily required for medical procedures. Manipulation of frame rate can be used to produce enormous savings in dose accumulation.

Lecture 5: Patient Dose Management

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36 Lecture 5: Patient Dose Management

Lecture 5: Patient Dose Management

36

37 Lecture 5: Patient Dose Management

Lecture 5: Patient Dose Management

37

38 Lecture 5: Patient Dose Management

Lecture 5: Patient Dose Management

38

39 Variable Pulsed Fluoroscopy

Variable Pulsed Fluoroscopy

Lesson: Variable pulsed fluoroscopy is an important tool to manage radiation dose to patients but the actual effect on dose can be to enhance, decrease or maintain dose levels. The actual effect must be estimated by a qualified physicist so that variable pulsed fluoroscopy can be properly employed.

Design of fluoroscopic equipment for proper radiation control

Lecture 5: Patient Dose Management

39

40 Collimation

Collimation

41 Collimation

Collimation

Lecture 5: Patient Dose Management

41

42 A word about collimation

A word about collimation

What does collimation do? Collimation confines the X ray beam to an area of the users choice.

Lecture 5: Patient Dose Management

42

43 Collimation

Collimation

Why is narrowing the field-of-view beneficial? Reduces stochastic risk to patient by reducing volume of tissue at risk Reduces scatter radiation at image receptor to improve image contrast Reduces scatter radiation to in-room personnel Reduces potential overlap of fields when beam is reoriented

Lecture 5: Patient Dose Management

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44 Scattered Radiation

Scattered Radiation

Lab Personnel

Patient

Operator

Two undesirable effects: (1) predominant source of radiation exposure to the laboratory personnel;

Lecture 5: Patient Dose Management

44

45 Scattered Radiation

Scattered Radiation

Two undesirable effects: (2) scattered radiation that continues in the forward direction and reaches the image receptor decreases the quality (contrast) of the image

Reduction of Image Contrast by Scattered Radiation

Lecture 5: Patient Dose Management

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46 Collimation: Contrast Improvement by Reducing X ray Beam Size

Collimation: Contrast Improvement by Reducing X ray Beam Size

Lecture 5: Patient Dose Management

46

47 Beam Orientation, Overlap and Collimation

Beam Orientation, Overlap and Collimation

Lesson: Reorienting the beam in small increments may leave area of overlap in beam projections, resulting in large accumulations for overlap area (red area). Good collimation can reduce this effect.

Lecture 5: Patient Dose Management

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48 Collimation

Collimation

In fact, dose at the skin entrance site increases, sometimes by a factor of 50% or so, depending on conditions.

What collimation does NOT do It does NOT reduce dose to the exposed portion of patients skin

Lecture 5: Patient Dose Management

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49 Factors that influence Patient Absorbed Dose

Factors that influence Patient Absorbed Dose

Equipment-related factors Movement capabilities of C-arm, X ray source, image receptor Field-of-view size Collimator position Beam filtration Fluoroscopy pulse rate and acquisition frame rate Fluoroscopy and acquisition input dose rates Automatic dose-rate control including beam energy management options X ray photon energy spectra Software image filters Preventive maintenance and calibration Quality control

Lecture 5: Patient Dose Management

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50 Lecture 5: Patient Dose Management

Lecture 5: Patient Dose Management

50

51 Lecture 5: Patient Dose Management

Lecture 5: Patient Dose Management

51

52 Field of View of Image Receptors

Field of View of Image Receptors

53 Equipment Selection

Equipment Selection

Angiography equipment of different FOV (Field of View)

9-inch (23 cm)

12-inch

dedicated cardiac image intensifier (smaller FOV, 23-25cm) is more dose efficient than a combined cardiac / peripheral (larger FOV) image intensifier larger image intensifier also limits beam angulation (difficult to obtain deep sagittal angulation )

Lecture 5: Patient Dose Management

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54 Dose rate dependence on image receptor active field-of-view or

Dose rate dependence on image receptor active field-of-view or

magnification mode.

In general, for image intensifier, the dose rate often INCREASES as the degree of electronic magnification of the image increases.

Lecture 5: Patient Dose Management

54

55 IMAGE INTENSIFIER

IMAGE INTENSIFIER

RELATIVE PATIENT ENTRANCE DOSE RATE FOR SOME UNITS

Active Field-of-View (FOV)

Lecture 5: Patient Dose Management

55

56 How input dose rate changes with different FOVs depends on machine

How input dose rate changes with different FOVs depends on machine

design and must be verified by a medical physicist to properly incorporate use into procedures. A typical rule is to use the least magnification necessary for the procedure, but this does not apply to all machines.

Lecture 5: Patient Dose Management

56

57 Beam Energy, Filter & kVp

Beam Energy, Filter & kVp

58 Image Contrast

Image Contrast

Object silhouette with no internal details

No object image is generated

Object image is generated

Lecture 5: Patient Dose Management

58

59 Effect of X ray Beam Penetration on Contrast, Body Penetration, and

Effect of X ray Beam Penetration on Contrast, Body Penetration, and

Dose

Lecture 5: Patient Dose Management

59

60 In general, every X ray system produces a range of energies

In general, every X ray system produces a range of energies

Higher energy X ray photons ? higher tissue penetration.

Beam energy:

High energy X rays: poor contrast and low skin dose

Low energy X rays: high image contrast but high skin dose

Middle energy X rays: high contrast for iodine and moderate skin dose

Lecture 5: Patient Dose Management

60

61 The goal is to shape the beam energy spectrum for the best contrast at

The goal is to shape the beam energy spectrum for the best contrast at

the lowest dose. An improved spectrum with 0.2 mm copper filtration is depicted by the dashes:

Beam energy:

Low-contrast high energy X rays are reduced by lower kVp

Filtration reduces poorly penetrating low energy X rays

Middle energy X rays are retained for best compromise on image quality and dose

Lecture 5: Patient Dose Management

61

62 kVp (kiloVolt-peak)

kVp (kiloVolt-peak)

kVp controls the high-energy end of the spectrum and is usually adjusted by the system according to patient size and imaging needs:

Beam energy:

Reproduced with permission from Wagner LK, Houston, TX 2004.

Lecture 5: Patient Dose Management

62

63 Comparison of Photon Energy Spectra Produced at Different kVp Values

Comparison of Photon Energy Spectra Produced at Different kVp Values

(from The Physical Principles of Medical Imagings, 2Ed, Perry Sprawls)

Lecture 5: Patient Dose Management

63

64 Filtration

Filtration

Filtration controls the low-energy end of the spectrum. Some systems have a fixed filter that is not adjustable; others have a set of filters that are used under differing imaging schemes.

Beam energy:

Reproduced with permission from Wagner LK, Houston, TX 2004.

Lecture 5: Patient Dose Management

64

65 Filter

Filter

Lecture 5: Patient Dose Management

65

66 Filtration  possible disadvantage

Filtration possible disadvantage

(1) Advantages -- they can reduce skin dose by a factor of > 2. (2) Disadvantages -- they reduce overall beam intensity and require heavy-duty X ray tubes to produce sufficient radiation outputs that can adequately penetrate the filters.

Filters:

Beam energy spectrum before and after adding 0.2 mm of Cu filtration. Note the reduced intensity and change in energies. To regain intensity tube current must increase, requiring special X ray tube.

Lecture 5: Patient Dose Management

66

67 Filtration potential disadvantage

Filtration potential disadvantage

If filters reduce intensity excessively, image quality is compromised, usually in the form of increased motion blurring or excessive quantum mottle (image noise). Lesson: To use filters optimally, systems must be designed to produce appropriate beam intensities with variable filter options that depend on patient size and the imaging task.

Lecture 5: Patient Dose Management

67

68 Dose vs

Dose vs

Noise

Lecture 5: Patient Dose Management

68

69 Efficient Dose and Image Quality Management

Efficient Dose and Image Quality Management

Achieving significant patient pose savings and yet keeping image quality at the same level

Detector Dose [?GY/s]

Patient Dose [cGY/min]

14

10

6

2

0.25

0.5

0.75

1

30cm water

Lecture 5: Patient Dose Management

69

70 Multiple Procedures

Multiple Procedures

71 Procedure Planning

Procedure Planning

Diagnostic coronary angiography ? PTCA Same day? Different day? Multivessel PTCA Treat all lesions during same procedure? Staged PTCA? Restenosis, Repeat Procedures

Lecture 5: Patient Dose Management

71

72 Dose Fractionation in Interventional Cardiology

Dose Fractionation in Interventional Cardiology

Reduce deterministic risk think of it as similar to risk of contrast-related nephropathy No significant impact on stochastic risk (? cumulative effective dose)

Lecture 5: Patient Dose Management

72

73 Effect

Effect

Dose

Deterministic effects

Stochastic

Cataract Infertility Erythema Epilation

Cancer Genetic Prob ? dose

Lecture 5: Patient Dose Management

73

74 Lab Personnel

Lab Personnel

Patient

Operator

Measures taken to reduce radiation exposure to patient will also benefit the operator/cath lab staff

Lecture 5: Patient Dose Management

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75 Revision Qs: True or False

Revision Qs: True or False

The higher the kVp, the higher the energy of the X ray photons, and the more contrast is the X ray image. When acquiring angiography with image intensifier, it is always better to use as magnified a field-of-view (FOV) as possible, because more details can be visualized.

Lecture 5: Patient Dose Management

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76 Revision Qs: True or False

Revision Qs: True or False

To avoid physical injury to patient, and to facilitate C-arm movement, it is advisable to keep the image receptor as far away from patient as possible. Patient has complex triple-vessel disease for angioplasty/stenting. Doing the angioplasty for all narrowings in one procedure will increase the risk of deterministic radiation injuries.

Lecture 5: Patient Dose Management

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77 Revision Qs: True or False

Revision Qs: True or False

Scattered radiation has no impact on the X ray image quality. Angiography table should be kept as near to the X ray source as possible. Keeping the same pulse intensity, reducing fluoroscopy pulse rate from 30 to 15 pulses/sec will reduce radiation dose to patient by 50%.

Lecture 5: Patient Dose Management

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Patient Dose Management
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