Hello, I'm MJ!

Atlanta. Restaurant Eugene

Atlanta Murphy's restaurant

애틀란타 보태니컬 가든 (Atlanta Botanical Garden) 근처에 있는 레스토랑.

1인 셰프가 운영하는 식당이고

집을 구하기 전이던 시절 자주 찾았던 곳이기도 하고

손님이 올 때나 이곳 친구들과 만날 때 애용하는 장소이기도 하다.

와인바도 갖춰져 있는데, 나는 한 번도 이쪽은 와보지 못했다.

전에 두번 정도 서빙해주었던 에밀리란 분이

주일 오전에 본인이 와인바 담당이라고 한 잔 하러 오라고 했었지만

주일이라 실패.

메뉴는 다양하다. 간단한 small plate 부터 샐러드, 메인 디시까지 있고

육류, 어류 다양하게 고를 수 있다.

매번 갈 때마다 메뉴를 열심히 고르지만

정작 먹는 것은 Today's Special.

서빙하는 분이 설명하는 거를 듣고 있다보면 '어머 저건 먹어야해'라는 생각이 들고

실제로 실패해본 적은 없는 것 같다.

내가 시킨 오늘의 메뉴는 Crab cream pasta with mushrooms, tomatoes, and sweet corns.

남편이 시킨 메뉴는 Trout 요리.

이것도 맛있다.

오늘은 기분 좀 내보려고 디저트도 먹고 왔다.

가장 인기가 많다는 Dessert Trio 와 아이스커피.

커피를 얼린 얼음을 넣어주어 마지막까지 연해지지 않고 맛있는 커피를 즐길 수 있었다.

1. Patient Care, Safety, and Communication

* ALARA principle (as low as reasonably achievable) [★]

- time, distance, shielding

- Complete diagnostic scan in a timely fashion at lowest output power that achieves a quality image

- Use the lowest transmit power that allows adequate tissue visualization

* Transmit power [★]

- Affect the exposure of the patient to acoustic power

- ↑ transmit power

: penetration ↑

: Acoustic power ↑, voltage applied to transducer elements ↑

: Image brightness ↑

* Bioeffect through absorption of sound energy by tissue [★★]

- Heating

: Tissue heating occurs when transmit power increases

* Nosocomial infection = hospital-acquired

- To avoid nosocomial & cross infection

: probe cleaning should always precede high-level disinfection

: covering probe with condom alone is insufficient

: disinfection using germicide compatible with the transducer

- When probe is in contact with mucous membranes

- Alcohol wipes are not recommended by manufacturers

: Alcohol degrade the transducer surface over time

* Mechanical index (MI)

- Method to evaluate bioeffect of US beam

 - Associated with onset of cavitation

* Thermal index (TI) [★]

- Power needed to increase tissue temperature by 1⁰C (Estimated temperature increase in tissue)

- TI > 1: Limit exposure time

- TI = 1: temperature could increase 1⁰C if transducer were held stationary

- most likely: bone (absorber)

- To avoid thermally induced biologic effects

: Avoid local tissue temperature increase exceeding 1⁰C

* Advantage of MI, TI

- Information available on screen to help sonographer implement ALARA principle

* Hydrophone

- Small needle with crystal at end

- Measure: amplitude (acoustic pressure), period, pulse duration (PD), PRP, PRF, duty factor (DF)

- Cannot measure: impedance

* String test object

- Evaluate doppler accuracy

* Acoustic streaming

- Acoustically generated transport of fluid within the body of insonated fluid/tissue

- Mechanical interaction of tissue and sound

- Motion of particles in a fluid observed in an intense US beam

2. Physics principles

* Purpose of gel coupling between transducer and skin

- To provide a medium for sound transmission, since US does not propagate through air

* Diffraction [★]

- General term for various phenomena in which waves from different parts of a source add or subtract

- ex) Pattern produced by a sound beam after passing through a small aperture

* When Image does not show adequate penetration, show noise in far field

- Decrease ultrasound transmit frequency [★★]

- Increase acoustic output

- Move focal zone to deeper position

* Doppler pulsed used for diagnostic purposes

- 5-30 cycles long

3. Pulse-Echo Instrumentation

* Tissue harmonics [★★]

1) Harmonic of transmitted frequency is used to create image

2) Harmonic frequency of transmitted pulse is generated within the body

- Selective reception of frequencies that are higher than that of transmitted frequency

generated within the body by nonlinear propagation

- Produces thinner beam

3) Advantage of Tissue harmonic imaging [★★]

- Grating lobe artifacts are reduced

               : improved contrast resolution

                              - contrast resolution is always improved by increasing frequency

                              - harmonics always result in use of higher frequency

                              - harmonics reduce clutter and side lobe artifacts

- lateral resolution is improved

- increase visualization of reflections from blood flow on real-time US image

* Signal-to-noise ratio

= relative amplitude of the signal compared to the amplitude of the noise

* Volume data set

1) Advantage

- Can be manipulated to show an infinite number of imaging planes with many different images

2) May be obtained by

- a freehand sweep of the probe over the anatomy

- an automated sweep of the transducer within the probe

3) Automated 3-D sweeps can be obtained with specially designed mechanical/electric transducers

- Advantage: Measurements can be accurately obtained

               (the distance of sweep is known)

* Cine loop

- Allows user to freeze and then scroll back through the most recently acquired image frames

* 3D imaging

1) Advantage [★★]

- Most helpful to obtain accurate anatomic volume measurements

- Ability to display image planes (coronal plane) impossible to obtain with 2D imaging

- Ability to display orthogonal planes simultaneously

2) volume rate: # of volumes displayed per second

3) Voxel

- smallest element of a 3-dimensional volume (3-dimensional pixel element)

- analogous to pixel in 2D imaging

* 4D imaging

- 3D imaging with addition of time

*

- Isotropic resolution: spatial resolution is equal in all planes

- Anisotropic resolution: unequal resolution between imaging planes

* Magnetic field tracking

1) Successful method of obtaining 3D data set

2) Based on a six degree-of-freedom magnetic field sensor

3) requirements for 3D reconstruction

- electromagnetic interference must be minimized

- transmitter must be in close proximity to receiver

- ferrous metals must not be within electromagnetic field

* DICOM (Digital Imaging and Communications in Medicine) [★]

- Standard for handling and transferring images and medical information

1) Query/Retrieve

- DICOM feature to recall a previous DICOM study onto system for viewing

2) Worklist

- DICOM feature to select patient name and automatically populate patient information on system.

3) Sonographic images are compressed before sending to PACS

- To reduce time to transmit the image

4) PACS (Picture Archive and Communication System)

- System commonly used to handle the archiving and electronic distribution of sonographic images

               (using a DICOM format)

* Advantage of Modality worklist

- Avoiding the need to type patient information

- Reducing patient information error

- Speeding up patient preparation time

- Easily confirming patient information

* Pulse inversion harmonics

1) Effective method to filter out fundamental frequency (transmitted frequency)

- leave only the harmonic frequencies for display

2) Uses two pulses of opposite polarity transmitted into the tissue in rapid succession

- The received echoes from the pulses are added together

- Cancels out the transmitted frequency, leaving the harmonics that were generated within tissue

* Cardiac output

- volume of blood pumped by the heart per minute

* Vessel wall layers

- Intima

: Single layer of cells backed by a thin layer of elastin and collagen fibers

               : atherosclerotic disease begins as a fatty streak within intima

- Media: contains smooth muscle fibers

* Rouleaux formation

- Stacking up of RBCs that occurs at low velocities and low shear rates

- Produces larger echo: blood flow may be visible

- velocity ↑ → rouleaux formation breaks up

4. Quality Assurance/Quality Control of Equipment

* SMPTE (Society of Motion Picture and Television Engineers) test pattern

- Standard pattern for evaluation of monitors and cameras

- Purpose: to aid in the setup and quality assurance of displays and cameras

* Quality control

1) system penetration

2) image uniformity

3) assurance of electric safety

4) distance measurement accuracy

* Dead zone

- distance from the transducer to the first identifiable echo

* sensitivity

- ability of the system to detect weak echoes

* transducers can be cleaned with

- soap and water

- ultraviolet light or radiation

- autoclave

- gas

- not) cidex, acetone, iodine, betadine, bleach

- Glutaraldehyde: commonly recommended ingredient in cleansers for intracavitary probes

Reference

* Davies Ultrasound Physics review

* https://sites.google.com/site/lindadmsportfolio/ultrasound-physics/

* https://sites.google.com/site/nataljasultrasoundphysics/

* https://sites.google.com/site/ektasphysicseportfolio/doppler

1. Artifacts

1) Any unintended information on an image that does not represent the object

2) Artifacts can be a hindrance or in some cases may be diagnostically helpful

3) Basic Assumptions

- There are several assumptions made by an ultrasound machine

- Artifacts occur when these assumptions are violated

1. Sound travels in a straight line

2. Reflections are produced by structures along the beams main axis

3. Sound travels at exactly 1540 m/s

4. Intensity of a reflection directly corresponds to a reflector’s scattering strength

5. The imaging plane is very thin

6. Sound beams travel directly to a reflector and back to source

2. Resolution Artifacts

1) Axial resolution artifact [★]

- Closely spaced targets of varying distances

- Axial Resolution

: Ability to differentiate between two objects along the long axis of the ultrasound beam

= SPL/2

- Axial Resolution Artifacts appear when all 3 conditions occur:

1. Two or more reflectors are closer together than SPL/2

2. Only one reflector will appear on the image

3. Reflectors are parallel to the beam axis

- Hindrance

: Produce fewer reflectors on the image

: Actual anatomic data is missing

- Prevention

: by using higher frequency transducers with short distinct pulses

2) Lateral Resolution Artifact [★★]

- Measuring lateral width of a target on an ultrasound phantom

- Lateral Resolution

: Ability to differentiate between two objects that lie perpendicular to the ultrasound   beam

= beam width

- Lateral Resolution Artifacts appear when all 3 conditions occur:

1. Two or more reflectors are closer together than the width of the beam

2. Only one reflector will appear on the image

3. Reflectors are perpendicular to the beam axis

- Hindrance

: Produce fewer reflectors on the image

: Actual anatomic data is missing

- Prevention

: by using narrower beams

3) Elevational Resolution Artifact (= Slice-Thickness A., partial volume artifact) [★★★★★]

-

- Due to beam width perpendicular to the scan plane.

- Affect imaging quality by displaying anatomic structures (reflectors) in the incorrect imaging plane

- These reflections can cause hollow structures to fill in

- Hindrance

: Causes anechoic structures to have low level echoes or false debris

- Example: false appearance of debris in simple cystic structure

- Prevention

1. Turn on Harmonics

: sound beam in this mode is narrower than in regular gray scale mode

2. Disc Shaped Elements

: Provide the thinnest slices and the best elevational resolution.

3. Newer Transducers

- 1.5-D arrays (multirow array transducer) [★★]

· They create thinnest beams with improved slice-thickness

· Have multiple crystals in an up and down direction

→ focus the beam in the thickness plane

· exhibit least amount of volume averaging

4) Contrast Resolution Artifact

- Inability of a gray-scale display to distinguish between echoes of slightly different intensities

: How many Shades of gray can be displayed

- Factoring Components

: With a decreasing number of bits per pixel, less shades of gray appear

- Less shades of gray = worse contrast resolution

- Cause: Not enough bits per pixel in image memory

- Poor contrast resolution

: Image appears more black-and-white, with few shades of gray in between

: Showing less detail

- Hindrance                                                                                                                              

: Fewer bits per pixel = fewer shades of gray = degraded contrast resolution

- Prevention: Usage of B Color

5) Spatial Resolution Artifacts

- Spatial resolution pertains to the overall detail produced in an image

- Spatial resolution artifacts are created when display monitor fail to produce adequate image detail

- Factoring Components: Spatial resolution artifacts can be created in a number of ways

1. Pixel Density

- Low pixel density (fewer pixels per inch) → larger pixels

: Larger pixels provide blurry and less detailed images

                              - Higher pixel density (more pixels per inch) → smaller pixels

                                             : Smaller pixels provide better detail, better spatial resolution

                              - pixel density cannot be changed

                              - quality may be improved by write magnification (pre-processing technique)

                                             : sonographer chooses a region of interest (ROI) to magnify

                                             : US rescans the image → greater number of pixels, improves SR

2. Line Density

- Low line density creates less detailed images

- controlled by US system, but can be controlled by the operator

- Modern display are equipped with more lines per page providing better SR

3. Number of horizontal lines in a display monitor. 

1. Resolution [★]

1) The ability to separate closely spaced objects

2) Types of Resolution

- Detail resolution: relating to the transducer

: Axial Resolution

: Lateral resolution

: Elevational Resolution

- Contrast Resolution: relating to the instrument

- Spatial Resolution: relates to instrument

- Temporal Resolution: Relating to the instrument

2. Axial Resolution= Longitudinal, Axial, Range/Radial Depth (LARD) [★★]

1) Accuracy in imaging parallel to beams axis. 

- The ability to accurately distinguish two reflectors as two reflectors parallel to the beam

2) Is a Number

- Depicts minimum separation that can be resolved

: Lower number = more accurate image (better axial resolution)

: Space between 2 reflectors less than AR = unresolved

· Structures will not be shown as individual structures 

: Space between two reflectors greater than AR = resolved

· Structures will be shown as individual structures

- AR [mm] = SPL/2 (best axial resolution with given transducer)

: spatial pulse length (SPL, [mm]) = # of cycles in a pulse x wavelength

: λ = c/f (wavelength = Propagating speed / frequency)

- propagating speed: determined by medium

- frequency: determined by source

: f↑- λ↓ - SPL↓ - AR↓(better axial resolution)

: pulse duration ↓ (bandwidth ↑) → SPL ↓ → better axial resolution

3) Superior AR

- AR depends on [★★★★]

: frequency (wavelength) - f↑ → better AR

: pulse duration (bandwidth) – PD ↓ → better AR

: higher bandwidth, increased damping → better AR

: AR is determined chiefly by pulse duration

- Increased focusing → beam width ↓ → better LR but pulse length ↑ (poorer AR)

4) Best measure of resolution for modern-day ultrasound: axial resolution

- cf) worst measure of resolution: elevational resolution

3. Lateral Resolution = Lateral, Angular, Transverse, Azimuthal (LATA) [★★]

-

1) Accuracy in imaging perpendicular to beam axis

- The ability to separate two reflectors as two reflectors perpendicular to the beam axis

- The minimum separation of two structures positioned side by side

2) Is a Number

- Depicts minimum separation that can be resolved

: Lower number = more accurate image (better lateral resolution)

: Space between 2 reflectors less than LR = unresolved

· Structures will not be shown as individual structures

: Space between two reflectors greater than LR = resolved

· Structures will be shown as individual structures

- LR [mm] = Beam diameter (beam width) [mm]

: Narrow Beams = Better LR. 

: Best at beam’s focus (end of near zone) 

3) Superior LR

- 3 things affect LR [★★]

1) Beam Aperture (diameter): Narrow/small is better

2) Distance from the transducer (T): Beam diameter varies with depth

3) Frequency: Higher frequency (narrower beam) is better

- to improve LR in far field: ↑frequency pulses diverge less in far field    

- primary method of improving LR: focusing, dynamic aperture, ↑ line density [★★★★★]

               : increase the number of transmit focal zones and optimize their location

4) Axial resolution is better than Lateral resolution for imaging

- US pulses are shorter than they are wide

- Higher frequency improves both

4. Slice Thickness/Elevational Resolution

1) The third dimension of the imaging plane, section thickness

- It is not thin or uniform

- True reflectors lie above/below assumed imaging plane but displayed on image                                                                                                                                                                           

2) Related to dimension of the beam perpendicular to the imaging plane [★★]

- Elevational resolution is worst with one-dimensional linear array transducer

- Elevational resolution is most affected by mechanical focus on linear array transducer

3) Contributes to image Artifacts

- Thicker portions: worse ER (worse artifact of image)

- Thinner portions: better ER (less artifact of image)

4) If using poor elevational resolution

- inability to clearly demonstrate small cystic structures

5. Contrast Resolution [★★★★]

1) ability of gray scale display to distinguish echoes of slightly different amplitudes and intensities

- ability to differentiate between two regions at different depths having similar echogenicity

- Better Contrast Resolution = Better detail

- improper adjustment → operator will likely over-gain or under-gain the image

2) Digital Displays [shades of gray]

- Pixel = picture element

: Smallest building block of image

- Entire pixel = single shade of gray

: Shade of gray determined by bits

- The more bits per pixel, the more shades of gray = better CR

               : 8 bit system produces a maximum of 2⁸ (256) possible shades of gray

               : n bit system → 2ⁿ shades of gray

- Dynamic Range/Shades of Gray

               : ratio of the largest to the smallest signal that a system can handle

: Determines the extent a signal can vary and maintain accuracy

: Narrow dynamic range = fewer shades of gray (High contrast)

: Wide dynamic range = many shades of gray (Low contrast)

- contrast resolution is improved by changing the gray-scale map

3) to improve contrast resolution: use 2D or matrix array transducer

- 2D (matrix array) transducer

               : have both rows and columns of elements

               → electronic focusing in the out-of-plane dimension possible (slice thickness is thinner)

               : contrast resolution is improved due to decreased volume averaging

6. Spatial Resolution

1) The overall detail of an image

- Greater detail images =↑Spatial Resolution

2) Determining factors [★]

- Line density: More scan lines = Better SR

: High line density (Sound pulses are closely packed) = better SR

: Low line density (Wider gaps between sound pulses) = worse SR

- reduce beam width (better SR) by focusing

- Axial resolution

- Lateral resolution

3) Digital Displays (pixel density)

- Pixel density: #of pixels per inch

: High pixel density = ↑SR (better image detail)

- Smaller pixel size

: Low pixel density = ↓SR (worse image detail)

- Large pixel size

4) higher frequency → better spatial resolution but greater attenuation

- to gain penetration: use lower frequency, sacrifice some spatial resolution

- for improved spatial resolution: use higher frequency, sacrifice penetration

7. Temporal Resolution

1) The ability of the display to distinguish closely spaced events in time

- Accuracy of displaying structures as they pertain to time

- The ability to precisely position moving structures from instant to instant

2) Determined by frame rate

- Frame Rate: # of frames (still images) displayed per second [★]

: Frame Time x Frame Rate = 1

(FR = 1/FT)

- More frames per second (higher frame rates) = Improved TR

3) Determining Factors of frame rate / Temporal resolution [★★★★★]

- Number of Pulses per frame

: Greater Line Density = ↑Frame Time, ↓Frame Rate (Worse TR)

- Multi focus: ↑ pulses per scan line, ↑Frame Time, ↓Frame Rate (Worse TR)

a. ↓pulses ↑ Frame Rate (Improved TR)

b. ↑pulses↓Frame Rate (Worse TR)

: Increase PRF = faster frame rate (improved TR)

: sector width ↑ → ↓Frame Rate (Worse TR)

- Depth of image

: Time of flight/Frame Time is directly related to depth

: Shallower Imaging

- shorter go return time, shorter Frame Time, higher Frame Rate (Superior TR)

: Deeper Imaging

- Longer go return time, longer Frame time, Lower Frame Rate (Inferior TR)

8. Frame Rate

1) Frame rate [★]

- Image formation

: Many single images are displayed in 1 second to produce “motion”

- How many frames pass in front of you per second

- similar to motion picture, multiple still images flashed in a rapid succession

- US examinations requiring highest frame rate: cardiac

- Determined by two factors

: Sound’s speed in the medium

: Depth of the image

- System settings that affect frame rate [★★]

: Image depth

: Number of pulses per frame (proportional)

               - PRF ↑ → frame rate ↑

- if scanning depth ↑, system automatically decreases PRF to avoid range ambiguity

- sector width ↑ → frame rate ↓

               : system fires more scan lines for each imaging frame

               → increase the length of time it takes to create each frame

- Determines Temporal Resolution

: Accuracy of displaying structures as it pertains to time

: Ability to precisely position moving structures from instant to instant

: Excellent when a system produces many frames per second

: Substandard when displays few images per second

2) Relationship between FR and Time

- FR = 1/FT

* Multiple transmit focusing [★]

1) beam must be fired once for each zone on each line of sight → reduce frame rate

- other types of focusing do not affect frame rate

2) Parallel processing (co-processing)

- method for improving frame rates with multizone electronic focusing

               : simultaneously acquiring data for multiple acoustic scan lines

Reference

* Davies Ultrasound Physics review

* https://sites.google.com/site/lindadmsportfolio/ultrasound-physics/

* https://sites.google.com/site/nataljasultrasoundphysics/

* https://sites.google.com/site/ektasphysicseportfolio/doppler