vibration sensitivity of optical microscopes in the h lth ......... in aisc dg 11dg 11 • all other...

Vibration sensitivity of yoptical microscopes in the

h lth ttihealthcare setting

Hal Amick, PhD, PE Michael Gendreau, INCE.Bd.Cert., Member

Colin Gordon & Associates

Paper 4aNS6 21 May 2009

OverviewOverview

• Review of current healthcare facilityReview of current healthcare facility vibration criteria

• Process of selecting criteria• Process of selecting criteria• Process of selecting design parameters• Case Study: Surgical microscope and its

criteria• Summary of criteria we use

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Paper 4aNS6: Amick & Gendreau, “Vibration sensitivity of optical microscopes in the healthcare setting”, 157th Meeting ASA, Portland, 2009

Current Healthcare Vibration CriteriaCurrent Healthcare Vibration Criteria

• Surgical SuitesSurgical Suites– 100 µm/s (4000 µin/s), as defined by ISO and

ANSI (rms one-third octave bands)ANSI (rms one third octave bands) – Misprinted as 200 µm/s (8000 µin/s) in AISC

DG 11DG 11 • All other spaces require engineering

judgment invoking criteria for other typesjudgment invoking criteria for other types of spaces

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Process of Selecting Criteria (1)Process of Selecting Criteria (1)

• How is vibration a problem?How is vibration a problem?– Human perception

• Startle• Distraction• Sleep interference

A• Annoyance– Affects instrument performance

• Degrades instrument performance• Degrades instrument performance• Introduces errors into data• Affects performance of person using instrument

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Process of Selecting Criteria (2)Vib i ff i P lVibrations affecting People

• Startle and distraction are critical conditions to avoid in surgical suites. – ISO and ANSI standards (hence ASHRAE and AISC) use factorISO and ANSI standards (hence ASHRAE and AISC) use factor

of safety (0.5) times human threshold of perception• Sleep interference is an important issue in patient

roomsrooms. – Sleep environment is basis of ISO/ANSI recommendations for

residential-nighttime limit of perception threshold. • Annoyance can be avoided in other areas by use of• Annoyance can be avoided in other areas by use of

“office” criterion from ISO, ANSI, ASHRAE, AISC.– Allows some perceptible vibration but avoids annoyance range.

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Process of Selecting Criteria (3)Vib i ff i IVibrations affecting Instruments

• Degrades instrument performance; may introduce errors g p yinto data. Most likely an issue with imaging (MRI and CT) and lab equipment (commonly microscopes).– Where possible, use instrument manufacturers’ criteria (MRI, CT, etc.)– Criteria for bench microscopes can be based on Amick & Stead,

ASHRAE, AISC

• Affects performance of person using instrument. Can lead to eye fatigue or worse (misreading or miscounting in lab tests; errors, nausea or annoyance with surgical microscopes)– Only criteria for surgical microscopes are from House & Randell,

referenced in AISC; discussed in later slides

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Benchtop Microscope Sensitivity, p p yOmnidirectional (Amick & Stead)

10000

1000 40x

100

Velo

city

, μ

m/s

1000x

400x

100x

10

rms

V

40x100x400x1000

1000x

11 10 100 1000

Frequency, Hz

1000x

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H. Amick and M. Stead, “Vibration Sensitivity of a Laboratory Bench Microscope,” Invited Paper, presented at the First Pan-American/Iberian Meeting on Acoustics; 144th Meeting of the Acoustical Society of America, 2-6 December 2002, Cancun, Mexico

Variation of Vibration Sensitivity i h M ifi i (A i k & S d)with Magnification (Amick & Stead)

y = 1995.1e-0.0027x

R2 = 0.9877

1000

10000

de,

μm/s With Newport Table

On Lab BenchExpon. (With Newport Table)Expon (On Lab Bench)

100

or A

mpl

itud Expon. (On Lab Bench)

AVC

y = 158.61e-0.0024x

R2 = 0.965110

Vert

ical

Flo B

C

10 200 400 600 800 1000 1200

Magnification, times

V

8

H. Amick and M. Stead, “Vibration Sensitivity of a Laboratory Bench Microscope,” Invited Paper, presented at the First Pan-American/Iberian Meeting on Acoustics; 144th Meeting of the Acoustical Society of America, 2-6 December 2002, Cancun, Mexico

Process of Selecting Design PParameters

• Footfall is generally the critical designFootfall is generally the critical design parameter

• Mechanical vibrations generally less thanMechanical vibrations generally less than those due to footfall unless something is defective or unless floor is very stiff (e.g., y ( gImaging and some MRI suites)

• Consider context in selecting footfall parameters

9

pPaper 4aNS6: Amick & Gendreau, “Vibration sensitivity of optical microscopes in the healthcare setting”, 157th Meeting ASA, Portland, 2009

Context-dependent Footfall P (1)Parameters (1)

• Footfall forces are a function of pace ratep• Walker pace rate is a function of path and

activity• Path issues• Path issues

– Closed path or corridor: long path, no obstructions – high walker rate (100 or 120 paces/min, we use 100)100)

– Open path or ghost corridor: long path, some obstructions – medium walker rate (80 to 85 paces/min we use 85)paces/min, we use 85)

– Patient room, lab room, or between lab benches:short path, obstructions – slow walker rate (70 to 80 paces/min we use 75)

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paces/min, we use 75)Paper 4aNS6: Amick & Gendreau, “Vibration sensitivity of optical microscopes in the healthcare setting”, 157th Meeting ASA, Portland, 2009


• Walker pace rate is a function of path and p pactivity

• Activity issues– Critical care: staff often in a hurry in the public

corridors – higher walker rate (consider 120 paces/min)p )

– Non-critical care: staff are less frequently in “hurried” mode in public corridor (consider 100 paces/min)Patient room: short path obstructions hard to– Patient room: short path, obstructions – hard to develop the gait associated with fast walker (70 to 80 paces/min, we use 75)

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• Perform multiple analyses usingPerform multiple analyses using appropriate walker forces applied at “soft” spots along walker path; base design onspots along walker path; base design on the condition creating maximum floor amplitudesamplitudes

• Vibrations due to walker at 75 ppm in room may be more severe than at 100room may be more severe than at 100 ppm in nearby corridor

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Case Study: The “established” criteria may need some rationalcriteria may need some rational

modification


Microscopic SurgeryMicroscopic Surgery• Some types ofSome types of

surgery require microscopy (10x tomicroscopy (10x to 50x)– OphthalmicOphthalmic– Spine

Paper 4aNS6: Amick & Gendreau, “Vibration sensitivity of optical microscopes in the

14

of optical microscopes in the healthcare setting”, 157th

Meeting ASA, Portland, 2009

Criteria?Criteria?• ASHRAE

– “Microsurgery, eye surgery, neurosurgery”, use 25 µm/s (1000 µin/s)

AISC / H & R d ll• AISC / House & Randell– Criterion of 50,000 / M µin/s, where M is

magnification, at frequencies between 3 and 8 Hz, g , q ,relaxed at higher frequencies; use 1250 µin/s (30 um/s) at 40x.

• Amick & Stead• Amick & Stead– Criterion of 100 um/s (4000 µin/s) for benchtop

microscope of 40x to 100x

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Case Study ProblemCase Study Problem

• Our client: A regional medical center withOur client: A regional medical center with four operating rooms, two dedicated to microsurgery using floor-mountedmicrosurgery, using floor mounted microscopes

One Leica one Zeiss– One Leica, one Zeiss• “Occasionally” there are vibrations which

cause the image to jigglecause the image to jiggle

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What we foundWhat we found …• Nice, stiff, concrete structure, ,• The “typical” ambient vibration environment in

these OR’s was below 50 um/s (2000 µin/s) (OR i i i 100 / )criterion is 100 µm/s)

• Footfall below 50 um/s (2000 µin/s)St d t t h t bl ji l• Steady-state has some acceptable jiggle

• “Problem”—high-amplitude jiggle—occurs a few minutes at a time a few times a dayminutes at a time, a few times a day

• One surgeon routinely experiences nausea during the “problem”

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g pPaper 4aNS6: Amick & Gendreau, “Vibration sensitivity of optical microscopes in the healthcare setting”, 157th Meeting ASA, Portland, 2009

Routine Floor Measurements(why such a problem?)

Vertical Floor Vibration - One-Third Octave Band10000

1000

during vibration inducedvisibility interferencewithout vibration inducedvisibility interferencePerception

Problem

100

Velo

city

, µm

/s

VC-A

10

rms

V

11 1.3 1.6 2 2.5 3.2 4 5 6.3 8 10 12.5 16 20 25 31.5 40 50 63 80

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One-Third Octave Band Center Frequency, Hz


Compare Floor and Eyepiece(in Narrowband)

a) Floor b) Eyepiece

Over 100 arc-sec at 50mm (explains nausea)

100

1000

w/ Interference

w/o Interference

100

1000

w/ Interference

w/o Interference

10

100

ocity

, um

/s

10

100

ocity

, um

/s12 Hz

24 Hz

1

rms

Velo

1rm

s Ve

lo

0.10 10 20 30 40 50

0.10 10 20 30 40 50

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Frequency, Hz0 10 20 30 40 50

Frequency, HzPaper 4aNS6: Amick & Gendreau, “Vibration sensitivity of optical microscopes in the healthcare setting”, 157th Meeting ASA, Portland, 2009

Compare Floor and Eyepiece(in Narrowband)

Ambient1000

w/ Visual Interference1000

100

1000

Eyepiece

Floor

100

1000

Eyepiece

Floor

10ocity

, um

/s

10

loci

ty, u

m/s

1

rms

Vel

1

rms

Vel

0.10 10 20 30 40 50

0.10 10 20 30 40 50

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Frequency, Hz Frequency, HzPaper 4aNS6: Amick & Gendreau, “Vibration sensitivity of optical microscopes in the healthcare setting”, 157th Meeting ASA, Portland, 2009

The ProblemThe Problem …

• Resonance amplification is a fact of lifeResonance amplification is a fact of life– 8 to12 Hz and 18 to 21 Hz, in this

configuration• Intermittent vibration from mechanical

equipment (12.0 Hz and harmonics) only slightly exceeded VC-A

• Improve the vibration isolation on the mechanical equipment

• Was VC-A adequate?

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What Criterion is Adequate?10000

Eqpt OnEqpt Off

What Criterion is Adequate?• Surgery

1000

10000

um/s

SurgeryVC-A10x (House & Randell)40x (House & Randell)100x (House & Randell)

g ycriterion notadequate

• VC A and10x

10

100

Velo

city

, u • VC-A and House & Randell 40x are

d t

40x

100x

1rms

V adequate• Consider

extending H&R0.1

1 10 100Frequency, Hz

extending H&R “dip” to the right or removing relaxation

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relaxationPaper 4aNS6: Amick & Gendreau, “Vibration sensitivity of optical microscopes in the healthcare setting”, 157th Meeting ASA, Portland, 2009

Proposed Modification to House & R d llRandell

• “Dip” in H&R 10 (H & R d ll)

pcriterion did not correspond to observed 1000

10000 10x (House & Randell)

40x (House & Randell)

100x (House & Randell)

Resonances

resonances• Solution:

Slide dip to100

Velo

city

, um

/s

3 - 8 Hz

– Slide dip to higher frequency

– Treat as single-velocity criterion

N.T.S.10

rms

V

velocity criterion, V=1250 / M(where M is magnification)

11 10 100

Frequency, Hz

8 - 13 Hz

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magnification)Paper 4aNS6: Amick & Gendreau, “Vibration sensitivity of optical microscopes in the healthcare setting”, 157th Meeting ASA, Portland, 2009

Vibration Criteria for Hospitals (1)Vibration Criteria for Hospitals (1)Type of Space

Primary Factor Criterion Rationale

This is defined by ISO and ANSI The established threshold of

Surgical Suites Human

100 µm/s (4000 µin/s)

This is defined by ISO and ANSI. The established threshold of human perception is 200 µin/s (8000 µin/s). Historically, the argument was that a factor of safety of 2 against perception avoided the risk of startling the surgeon. [Misprinted as 8000 µin/s in AISC DG 11.Correct in ASHRAE]

30 µm/s AISC DG 11 based on research by House and Randell validatedSurgical Suites

40x Surgical Microscope *

30 µm/s (1250 µin/s)

AISC DG 11, based on research by House and Randell, validated by Gendreau

Surgical 100x Surgical 12.5 µm/s (500 i / )

AISC DG 11, based on research by House and Randell Surgical Suites

100x SurgicalMicroscope *

(500 µin/s)(VC-C)

Patient Rooms Human 200 um/s

(8000 µin/s)

This is not specifically defined by international standard (differing from the case for surgical suites), but is based upon the international standard for sleeping areasRooms (8000 µin/s) international standard for sleeping areas.

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Vibration Criteria for Hospitals (2)Vibration Criteria for Hospitals (2)Type of Space

Primary Factor Criterion Rationalep

General Labs Instrument

50 µm/s (2000 µin/s)

(VC-A)

This is a consensus standard from a wide variety of sources, including ASHRAE, AISC, IEST, and NIH for generic laboratory space with microscopes up to 400x.

General Labs Instrument 100 µm/s

(4000 µin/s)

This is a relaxed criterion for “non-critical” laboratories with microscopes of 100x or less. Used by many universities for teaching labs (i.e., labs not used for research)

Imaging12.5 µm/s Imaging systems vary widely in their sensitivity. The 500 µin/s

criterion (approximately) is required to meet the needs of a few ofImaging Labs (MRI) Instrument (500 µin/s)

(VC-C)

criterion (approximately) is required to meet the needs of a few of the available systems. By eliminating those from consideration, the criterion can be relaxed.

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ReferencesReferences• AISC DG 11: Murray, Thomas M., David E. Allen, and Eric E. Ungar (1997), “Floor Vibrations

Due to Human Activity," Steel Design Guide Series 11, American Institute of Steel Construction, y, g , ,69 pp.

• Amick and Stead: H. Amick and M. Stead, “Vibration Sensitivity of a Laboratory Bench Microscope,” Invited Paper, presented at the First Pan-American/Iberian Meeting on Acoustics; 144th Meeting of the Acoustical Society of America, 2-6 December 2002, Cancun, Mexico

• Amick and Stead: H. Amick and M. Stead, “Vibration Sensitivity of a Laboratory Bench Mi ” S d & Vib ti 41 N 2 10 17 (F b 2007)Microscope,” Sound & Vibration, v. 41, No. 2, pp. 10-17 (February 2007).

• ASHRAE: ASHRAE (2003). ASHRAE Handbook: Applications, Chapter 47 (Fig. 39 & Table 40), “Sound and Vibration Control,” 50 pp.

• House and Randell: House, M. H., and Randell, R. (1987). “Some Measurements of Acceptable Levels of Vibration in Scientific, Medical and Ophthalmic Microscopes,” Proc. SPIE Conf. Vib. Con Opt and Metrology 732 pp 74 80 [ V = 1250 / M um/s where M is magnification ]Con. Opt. and Metrology 732, pp. 74-80 [ V = 1250 / M um/s, where M is magnification ]

• IEST: Institute of Environmental Sciences and Technology, “Considerations in Cleanroom Design,” RP-CC012.2, 2005.

• ISO: International Standards Organization, ISO 2631 "Mechanical vibration and shock -Evaluation of human exposure to whole-body vibration, Parts 1 and 2." Part 1 was updated 15 July 1997 and Part 2 was updated 1 April 2003July 1997 and Part 2 was updated 1 April 2003.

• NIH: National Institutes of Health, Office of Research Fachilities (Spring 2003). NIH Design Policy and Guidelines

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Thank youThank you

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