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Practical Guide for Three-Dimensional Transthoracic Echocardiography Using a Fully Sampled Matrix Array Transducer Hyun Suk Yang, MD, PhD, Ramesh C. Bansal, MD, FASE, Farouk Mookadam, MBBCh, Bijoy K. Khandheria, MD, FASE, A. Jamil Tajik, MD, FASE, and Krishnaswamy Chandrasekaran, MD, FASE, Scottsdale, Arizona; and Loma Linda, California Continuing Medical Education Activity for “Practical Guide for Three-Dimensional Transthoracic Echocardiography Using a Fully-Sampled Matrix Array Transducer” Accreditation and Disclosure: The American Society of Echocardiography is accredited by the Accreditation Council for continuing Medical Education to provide continuing medical education for physicians. The American Society of Echocardiography designates this activity for a maximum of 1.0 AMA PRA Category 1 Credits™. Physicians should only claim credit commensurate with the extent of their participation in the activity. ARDMS and CCI recognize ASE’s certificates and have agreed to honor the credit hours towards their registry requirements for sonographers. The American Society of Echocardiography is committed to resolving all conflict of interest issues, and its mandate is to retain only those authors with financial interests that can be reconciled with the goals and educational integrity of the educational activity. Disclosure of faculty and commercial support sponsor relationships, if any, will be made known before the activity. Target Audience: Participation should include clinicians and sonographers involved in echocardiography. Objectives: Upon completing the reading of this article the participant should be able to (1) recognize the basic terminology and technology of 3D echo using a fully-sampled matrix array transducer, (2) assess the practical steps of 3D data acquisition and analysis, and (3) understand clinical applications to effectively use the 3D TTE technology. Estimated time to complete this activity: 1 hour Real-time three-dimensional (3D) echocardiography is a major innovation in the history of cardiovascular ultrasound. Advances in computer and transducer technologies, especially the fully-sampled matrix array transducer, have permitted real-time 3D image acquisition and display. Several vendors provide 3D imaging but use different terminology for similar functions, creating confusion for consumers. This article provides a practical guide on how to acquire and analyze 3D images on-cart using currently available ultrasound systems (iE33, Philips Medical System, Andover, MA; Vivid7, GE Healthcare, Wauwatosa, WI) in daily clinical practice. (J Am Soc Echocardiogr 2008;21;979-989.)

Keywords: 3D echocardiography

Three-dimensional (3D) ultrasound systems for the human heart appeared in 1974. This early ultrasound technique produced a sequential stack of 2-dimensional (2D) images without gating.1 The clinical use of 3D echocardiography has been limited because of time-consuming and complicated image acquisition and postprocessing, until more recently as advances in ultrasound and computer technology have mitigated these problems. In the 1990s, the firstgeneration volumetric real-time 3D transthoracic echocardiography (RT3D TTE) systems were introduced2,3 using sparse-array matrix transducers (2.5-3.5 MHz, 256 elements) that significantly reduced acquisition times. However, the 3D data sets were sliced to view only 2D-like images with relatively low spatial resolution. 3D echocardiography reached a major milestone shortly after 2000 with the advent of second-generation RT3D TTE, having fully sampled matrix array transthoracic transducers (⫻4 probe, 2.0-4.0 MHz, 2880 elements; ⫻3-1 probe, 1.0-3.0 MHz, 2400 elements; ⫻7-2 probe,

From the Division of Cardiovascular Diseases, Mayo Clinic, Scottsdale, Arizona (H.S.Y., F.M., B.K.K., A.J.T., K.C.); and Loma Linda University Medical Center, Loma Linda, California (R.C.B.). Reprint requests: Krishnaswamy Chandrasekaran, MD, FASE, Mayo College of Medicine, Division of Cardiovascular Disease, Mayo Clinic, 13400 East Shea Boulevard, Scottsdale AZ 85259 (E-mail: [email protected]) 0894-7317/$34.00 Copyright 2008 by the American Society of Echocardiography. doi:10.1016/j.echo.2008.06.011

2.0-7.0 MHz, 2500 elements [all from Philips Medical Systems, Andover, MA]; 3V probe with 1.5 to 3.6 MHz, “thousands” of elements [GE Healthcare, Wauwatosa, WI]) offering on-cart 3D rendered images with good image quality and shorter acquisition times using a standard ultrasound machine.4 By 2007, real-time 3D transesophageal echocardiography using a fully sampled matrix array transducer (X7-2t probe with 2.0-7.0 MHz, 2500 elements) offered 2D, Doppler, and 3D imaging in a single probe with excellent spatial resolution, ease of use, and time efficiency. The clinical applications of a fully sampled matrix array transducer’s RT3D TTE and its strengths have been described in 2 comprehensively referenced recent review articles.5,6 In brief, one of the most important current clinical applications is to provide optimal left ventricular (LV) volume measurements.7 Geographically more challenging anatomic chambers, such as the right ventricle (RV) or left atrium (LA), are also attractive targets for 3D TTE volume measurement.8-10 In addition, 3D TTE has improved the assessment of valvular heart disease,11-18 congenital heart disease,19-21 and cardiac dyssynchrony,22 and has demonstrable time-efficiency in stress echocardiography23-26 (Table 1 and Supplementary document). The advantages of RT3D TTE have been clearly demonstrated. In an effort to advance this technology from the research arena to general clinical practice, it is useful to have a practical guide on how to acquire and analyze 3D images on-cart with standard echocardiography systems in daily clinical practice. The purpose of this article is to present basic 3D knowledge and methodology to sonographers wanting to adopt 3D ultrasound technology. To understand the 979

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Table 1 List of clinical applications using a fully sampled matrix-array 3-dimensional transthoracic echocardiography probe (PubMed February 2008) (references are online in Supplementary document) Quantity of articles*

Cardiac chambers LV volume LV mass LV intraventricular asynchrony RV volume LA volume Valvular heart disease Mitral valve evaluation Mitral valve prolapse: localization Mitral regurgitation: geometry, quantification Mitral stenosis: valve area Aortic valve stenosis: valve area or geometry Tricuspid valve: rheumatic, pacing leads, and so forth Pulmonic valve: vegetation, fibroelastoma, and so forth Cardiac mass Endocarditis Other intracardiac mass: tumors, thrombi, and so forth Congenital heart disease Atrial septal defect†: area or geometry Ventricular septal defect: area or geometry Outflow obstruction: HCM, subaortic membrane Noncompaction Stress echocardiography (with or without contrast) Myocardial perfusion Intraoperative epicardial echocardiography Procedural guidance

30 17 12 9 9

(30) (17) (12) (9) (9)

26 7 10 9 5 19 3

(25) (6) (10) (9) (4) (14) (1)

7 (0) 13 (2) 18 8 9 8 8 2 4 7

(11) (6) (4) (1) (8) (2) (3) (3)

LV, Left ventricular; RV, right ventricular; LA, left atrium; HCM, hypertrophic cardiomyopathy. *Quantity indicates total quantity of English language, human subject original research articles, and case reports; parenthetical quantity is original research articles only. †Includes atrioventricular septal defect.

historical background of 3D image reconstruction and display27,28 and its current clinical applications, we recommend these previous outstanding articles as references.5,6 IMAGE ACQUISITION AND ON-CART ANALYSIS Ultrasound Equipment and System The transducer characteristics and image processing algorithms of currently available real-time 3D TTE ultrasound systems are shown in Figure 1 and Table 2. The information in the table outlines operating features and terminology with no implication that one or the other system is superior. A fully sampled matrix array transducer technology allows the ultrasound beam to be steered along the familiar 2D X- (lateral: left and right) and Y-axes (vertical: up and down), but adds the Z-axis (front and back) (Figure 1). Image Acquisition Modes RT3D TTE generally has 4 acquisition modes: 1) live 3D, 2) 3D zoom, 3) full-volume, and 4) 3D color Doppler. 1) “Live 3D” is a button or mode used to switch the system from 2D mode into true RT3D to watch and acquire real-time 3D volumetric motion without electrocardiography (ECG)-gated reconstruction. 2) “3D Zoom” mode displays a focused volume of interest (VOI), defined by a

Figure 1 3D TTE ultrasound orientation (left) and the transducers (right) for the iE33 (Philips Medical Systems, Andover, MA) (A: 2D vs. B: 3D), and Vivid7 (GE Healthcare, Wauwatosa, WI) (D: 2D vs. C: 3D) ultrasound system. The size and area of the footprints are: S5-1 probe (2.4 ⫻ 1.5 cm, 3.5 cm2), ⫻3-1 (2.6 ⫻ 1.6 cm, 4.2 cm2), 3V (2.5 ⫻ 2.1 cm, 5.0 cm2), M3S (2.3 ⫻ 1.6 cm, 3.7 cm2). Color figure online. truncated slice of an arbitrary sector angle, in greater detail with or without ECG gated reconstruction. iE33 3D zoom allows various ranges of real-time volumetric images up to 90 ⫻ 90 degrees, although the frame rate is substantially reduced to compensate. 3) “Full-volume” 3D combines a series of subvolumes acquired with ECG gating to create a final, larger, reconstructed full volume image. 4) “3D color Doppler” mode combines gray-scale volumetric data with color Doppler. These modes are illustrated in Figure 2. Live 3D (ECG Recording) Versus Full-Volume 3D (ECG gating): Advantages and Disadvantages The broad term “real-time” is typically applied to all current 3D echocardiography images to distinguish them from earlier generations of complicated, reconstructed 3D images. However, the above 4 modes fit into 2 basic types: some of these (eg, live 3D) are true real-time, using simultaneous ECG recording, whereas others (eg, full-volume) use ECG gating to synchronize image portions accumulated over sequential cardiac cycles and are near-real-time, the full image being unavailable until the final recorded cycle is complete. In this article, to avoid some confusion, we use “real-time” to mean true real-time and “ECG gated” or “reconstructed full-volume” as its complementary, near-real-time type. There are advantages and limitations for each type, as exemplified by “live 3D” and “full-volume” modes. Live 3D offers artifact-free instantaneous feedback but is limited to a narrow angle with a partial volume and may not provide much information. In real-time (live) 3D zoom acquisition, if the angle sector is too small, it may loose its spatial orientation to other structures, for example, a ventricular septal defect in relation to an outflow tract; full-volume 3D gathers data over multiple cardiac cycles using ECG gating, yielding superior sector angles, frame rates, or line density (because the full power of the echo system is being incrementally applied to a smaller volume per cycle), but opens the door to potential intercycle/subvolume image stitching artifacts, rendering these images unsuitable for patients with arrhythmia or respiratory instability. Furthermore, image availability is delayed until after the last cycle is recorded. Thus, live 3D is generally recommended for interventional guidance, rhythm disturbances, and any situation in which the VOI is within live 3D’s limited angle. Real-time (live) 3D zoom acquisition for valvular and smaller structures such as a thrombus is preferable to avoid stitch artifacts; a wide-angle, full-volume mode is recommended in LV or RV volumetric measurement or cardiac dyssynchrony studies.

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Table 2 Currently available real-time 3-dimensional transthoracic echocardiography systems iE33 Philips Medical Systems, Andover, MA

A fully sampled matrix array transthoracic transducer Name Frequency, MHz Footprint, cm2 Doppler in 2D Biplane Triplane Vender-specific terminology 3D (with time) Bi- or triplane 2D orthogonal slices Sector size, resolution Live 3D Type Sector angle Position options Gain Thick slice 3D zoom Types Sector angle Full-volume Type Sector angle Maximum FPS in 10-cm depth Biplane preview screen Live reference screen 3D color Types Sector angle Image rendering Simple 1-touch crop Box crop Arbitrary plane crop Pair (box, plane crop; plane, box crop) Flip Options Stereoscopic vision 9-slices 3D color 6-slices 3D Grid Data storage and software Create subpage DICOM to media One full-volume, MB On-cart software Off-line software

X3-1

Vivid7 GE Healthcare, Wauwatosa, WI

3V 1.0-3.0 4.2

1.5-3.6 5.0

No Lateral or elevation tilting No

Yes Lateral tilting Yes

3D ⫻Plane MPR mode Density (low, medium, high)

4D Multiplane Slice mode Volume size (3 grades)

Real-time Fixed (2 selections) Lateral or elevation (back, center, front) TGC, LGC Yes

Real-time Variable Elevation (tilt: 3 selections) LGC No

Real-time Up to 90 ⫻ 90 degrees

Real-time or ECG gated full-volume (2, 3, 4, or 6 cycles) Up to 90 ⫻ 20 degrees

ECG-gated full-volume (4, 5, or 7 cycles) Up to 101 ⫻ 104 degrees 42 (92 ⫻ 83 degrees) Full range of elevation No

ECG-gated full-volume (2, 3, 4, or 6 cycles) Up to 82 ⫻ 80 degrees 39 (82 ⫻ 80 degrees) One segment of elevation Yes

ECG-gated full-volume (7, 10, or 14 cycles) Up to 60 ⫻ 60 degrees

Real-time or ECG-gated full-volume (4 or 7 cycles) Up to 25 ⫻ 25 degrees

Auto-crop (1 direction) Yes Via moving plane or object First crop kept

Angle (3 directions) Yes Via moving plane First crop lost

No Overall 3D gain Compress Bright Smoothing

Yes Overall 2D and 4D gain Volume optimize (Gamma, Shading, Smoothness) UD clarity Yes (glasses) Any orientation and span, uniformly spaced planes Yes No

No Horizontal, uniformly spaced planes No Yes Yes Full study or selected clips 15-50 QLAB QLAB 6.0 Xcelera

No Full study 50-80 EchoPAC, TomTec LV EchoPAC 2008 workstation

MPR, Multiplanar reconstruction; TGC, time gain compensation; LGC, longitudinal gain compensation; 2D, two-dimensional; 3D, three-dimensional; ECG, electrocardiography; FPS, frames per second; DICOM, digital imaging and communication in medicine; UD, ultra definition.

Examination Protocol: Complete or Focused At present there is no well-recognized, universally accepted protocol available. Live or full-volume 3D images are expected to provide the entire relevant volume of morphologic and functional details, but in most patients, the decrement in spatiotemporal resolution and penetration that results from increasing the sector angle does not permit a comprehensive examination from a single transducer location. To overcome the current technologic limitations of spatiotemporal res-

olution, penetration, and sector angles, 3D images should be acquired from multiple transducer positions. A complete 3D TTE examination would require 4 transducer positions: 1. parasternal, 2. apical, 3. subcostal, and 4. suprasternal (Table 3). In clinical practice, many 3D echocardiography examinations are focused rather than complete. An anatomically oriented focused 3D echocardiography examination is shown in Figure 3. The indications for performing 3D TTE imaging are variable; a modification of the acquisition protocol addressing the

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Figure 2 Four acquisition modes of the iE33 (Philips, upper) and Vivid7 (GE, lower): Live 3D, 3D zoom, Full-volume, and 3D Color mode. Color figure online.

Table 3 Example of a complete 3-dimensional transthoracic echocardiography protocol 1. At the parasternal position Wide-angle (full-volume) of the long-axis view Narrow angle (live 3D) 3D color of AV, MV, TV*, and IVS Zoom of the parasternal short axis of AV, MV, and TV* 3D color of the modified parasternal short axis of PV Zoom of the modified parasternal short axis of PV 2. At the apical position Wide-angle (full-volume) of apical 4-chamber view If needed, focus LV and LA, RV and RA, sequentially Narrow angle (live 3D) 3D color of MV, AV, and TV Zoom of MV, TV, IAS, and IVS 3. At the subcostal position Wide-angle (full-volume) 3D color of IAS 4. At the suprasternal notch position Wide-angle (full-volume) 3D color of arch and descending aorta AV, Aortic valve; MV, mitral valve; TV, tricuspid valve; PV, pulmonic valve; LV, left ventricle; RV, right ventricle; LA, left atrium; RA, right atrium; IAS, interatrial septum; IVS, interventricular septum. *TV image at low parasternal position.

specific indication should be undertaken as a focused examination. For instance, in a patient with congestive heart failure in whom LV volume, ejection fraction, and the dyssynchrony index are needed, one can use the apical window and acquire a 3D full volume data set; if the valves are of concern, the appropriate window for that particular valve with optimal visualization should be chosen. For mitral valve assessment, a full-volume or wide sector real-time 3D zoom mode from either parasternal or apical windows is recommended. One study16 suggested that the posterior leaflet was best seen from a parasternal view; the anterior leaflet was best visualized from an apical window, particularly as seen from a ventricular perspective. For the aortic valve, a live 3D or narrow sector real-time 3D zoom mode from the parasternal window with as high a density as possible is recommended. (Higher spatiotemporal resolutions produce nar-


Figure 3 Focused 3D TTE examinations according to cardiac anatomy. Color figure online. rower sectors, and vice versa.) A few general guidelines for the focused examination: First, start with live 3D and switch to fullvolume only if the focused VOI is larger than the live 3D or zoom sector size; second, in cases with rhythm or respiratory disturbances, try to stick to a real-time mode; third, choose the highest resolution option possible that accommodates the VOI (the density options in iE33, volume size options in Vivid7). Step-by-Step Image Acquisition Firstly, choose a fully sampled matrix array transducer (X3-1 for iE33, 3V for Vivid7) and its application, and optimize the ECG tracing to ensure a distinct R-R voltage via the “Physio” setting (choose ECG leads, optimize gain, and position). On the iE33, confirm the current 3D live capture type (Setup\Print Network\Prospective or Retrospective capture) and set the number of beats for live 3D capture via “loop”—the number of cycles for full-volume is a dependent variable derived from the 2 independent factors (density and optimize knob options; Tables 4 and 5). “Density” has 3 options (low, medium, and high), which reflect the line density in a single pyramidal data set; a higher density effects a narrower angle sector. The “Optimize” knob has 3 options: optimize volume size (allows the widest, largest volume— eg, dilated LV), optimize acquisition beats (the smallest number— eg, respiration control is weak), and optimize frame rate (more frames per second— eg, dyssynchrony). For the Vivid7, set the number of beats for live 3D capture (Config\Imaging\Application\Number)—the number of cycles for the full-volume image will be set independently before acquiring any individual images (Default 4; 2, 3, 4 and 6 in gray-scale full-volume; 4 or 7 in color full-volume), affecting final volume size (Tables 6 and 7). Vivid7’s “Volume Size” option is inversely comparable to iE33’s “Density”— increasing the volume size decreases the image line density (ie, decreases the spatial resolution). For the widest final volume, choose 6 cycles and the largest volume size; for higher resolution, choose the smallest volume size. The image acquisitions steps for each system and image acquisition optimizing tips are summarized in Table 8. In principle, 2D imaging needs to be optimized first—suboptimal 2D images produce suboptimal 3D images, and any ECG-gated, full-volume acquisition requires skill to avoid reconstruction (stitching) artifacts: The patients must hold very still, suspending breathing, and the operators must stabilize the probe. Postprocessing: Image Rendering The real advantages of 3D echocardiography come after acquisition of the entire VOI. By using the image-rendering process on the

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Table 4 Full-volume mode “density” and “optimize knob” options in iE33 ultrasound (Philips), 10-cm depth Density

Low FPS, Hz L⫻E No. of cycle, n Medium FPS, Hz L⫻E No. of cycle, n High FPS, Hz L⫻E No. of cycle, n

Optimize volume size

Optimize acquired beats

Optimize frame rate

22 101 ⫻ 104 degrees 5

24 92 ⫻ 83 degrees 4

42 92 ⫻ 83 degrees 7

27 94 ⫻ 86 degrees 7

24 76 ⫻ 69 degrees 4

42 76 ⫻ 69 degrees 7

27 75 ⫻ 69 degrees 7

24 61 ⫻ 55 degrees 4

42 61 ⫻ 55 degrees 7

FPS, Frames per second; L, lateral plane sector angle; E, elevation plane sector angle.

Table 5 Three-dimensional color mode “density” and “optimize knob” options in iE33 ultrasound (Philips), 10-cm depth Density

Low FPS, Hz L⫻E No. of cycle, n Medium FPS, Hz L⫻E No. of cycle, n High FPS, Hz L⫻E No. of cycle, n

Optimize volume size

Optimize acquired beats

Optimize frame rate

8 60 ⫻ 60 degrees 10

12 41 ⫻ 41 degrees 7

24 41 ⫻ 41 degrees 14

8 50 ⫻ 50 degrees 10

12 35 ⫻ 35 degrees 7

24 35 ⫻ 35 degrees 14

8 40 ⫻ 40 degrees 10

12 28 ⫻ 28 degrees 7

24 28 ⫻ 28 degrees 14


Table 6 Full-volume mode “volume size” and “number of cycle” options in Vivid7 ultrasound (GE), 10-cm depth, 1.7/3.5 MHz No. of cycles, n Volume size

1 (small) FPS, Hz L⫻E 2 (medium) FPS, Hz L⫻E 3 (large) FPS, Hz L⫻E

2

3

4

6

30.4 35 ⫻ 35 degrees

30.4 45 ⫻ 45 degrees

29.9 52 ⫻ 52 degrees

39.1 55 ⫻ 55 degrees

29.0 45 ⫻ 45 degrees

30.4 52 ⫻ 53 degrees

29.0 64 ⫻ 64 degrees

37.9 68 ⫻ 68 degrees

29.0 53 ⫻ 53 degrees

30.4 64 ⫻ 64 degrees

29.9 77 ⫻ 76 degrees

39.1 82 ⫻ 80 degrees


machine, we can see the complex spatial relationships with an en face view or surgeon’s view, which sometimes cannot be produced by 2D echocardiography. The purpose of image rendering is to both perspicaciously and perspicuously display a VOI with a desired orientation. To do this, we go through 3 steps: cropping, thresholding, and displaying. In 3D echo, the volumetric data permits sectioning the 3D image and allows looking inside of the volume image. For a quick inspection on the iE33, use “Auto-crop,” which removes the front half (fullvolume) or a quarter (live 3D) of the image from the display; on the Vivid7, the “Angle” button offers 3 standard-direction cropped views.

Cropping or segmentation of a volume removes volume information that is unwanted and allows us to demonstrate the pathology involved. For instance, in mitral valve prolapse a cropping tool can be used to cut away the top or lateral wall of the LA to view the mitral valve from an LA orientation. There are 2 common cropping modules: X-Y-Z box (Figure 4A) and single arbitrary plane (Figure 4B). Thresholding allows us to determine how much of the volume data information is seen as an anatomic structure or deemed part of the cavity. This is mainly determined by gain settings (overall gain, time gain compensation, and longitudinal gain compensation with the iE33; 2D gain, 4D gain, and longitudinal gain compensation with

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Table 7 Four-dimensional color mode of real-time and reconstructed full-volume “volume size” and “number of cycle” options for Vivid7 ultrasound (GE), 10-cm depth, 1.7/3.5 MHz, Scale 3.5 kHz Full-volume No. of cycles, n Volume size

1 (small) FPS, Hz L⫻E 2 (medium) FPS, Hz L⫻E 3 (large) FPS, Hz L⫻E

Real-time

4

7

16.7 14 ⫻ 14 degrees

32.5 9 ⫻ 13 degrees

35.0 19 ⫻ 14 degrees

8.6 13 ⫻ 13 degrees

18.0 11 ⫻ 15 degrees

16.0 17 ⫻ 20 degrees

8.6 20 ⫻ 20 degrees

15.7 18 ⫻ 21 degrees

15.7 25 ⫻ 25 degrees


Table 8 Image acquisition steps in each 3-dimensional mode

Live 3D Start 3D setting

Size

Position

Reference Save 3D Zoom Start Size Position Save Full-volume Start Size Position Acquire Check

Reject Save 3D Color Start Size Position

iE33 Philips Medical Systems

Vivid7 GE Healthcare

Press Live 3D Gain: 50% (0-100) TGC, LGC Compress: 50 dB (0-100) Choose Density: Med (55 ⫻ 29 degrees) or High (44 ⫻ 23 degrees) (Cannot change width/thickness) Adjust Depth knob Thick Slice (90 ⫻ 4 degrees) 59 Hz at 10 cm Lateral: Lateral Steer knob Elevation: Back, Center, or Front Rotation: trackball; to reset, 3D Home Optional: press Image, choose reference icons Press Acquire

Press 4D 2D gain: to see valves 4D gain: to see back of chamber LGC: Top zero, automatic Adjust Volume Size (3 grades) Default: 50 ⫻ 15 degrees, 50 ⫻ 22 degrees, 50 ⫻ 31 degrees Adjust Width knob; thickness varies implicitly to conserve total volume Adjust Depth knob Lateral: fixed Elevation: Adjust Tilt or Press Front/Back key (direction) Rotation: trackball; to reset, Clear Automatic reference screen Press Img Store

Press 3D Zoom ¡ biplane preview screen Left box: X-,Y-axis by trackball Right box: Z-axis, Elevation Width knob Left box: X-, Y-axis by trackball Right box: Back, Center, or Front Press 3D Zoom, choose Density, then Acquire

Press HR Zoom, adjust ROI in 2D plane, size/position by trackball, then press 4D If real-time: adjust Width & Volume Size knob, press Img Store If full-volume: adjust Volume Size, Num. Cycles, press Full Volume then Img Store, adjust Cycle Select Press Img Store

Press Full Volume ¡ biplane preview screen Density: Low, Med, or High Optimize knob: Volume Size, Acq Beats, or Frame Rate Fixed Press Acquire During patient’s breath-hold Full-volume is displayed as an auto-crop; Press Reset Cropping and roll the trackball down to examine stitch artifacts Press Reject Full Volume Press Accept Full Volume Press Color, then Full Volume ¡ biplane preview screen Density: Low, Med, or High Optimize knob: Volume Size, Acq Beats, or Frame Rate Depth by trackball X-, Y-axis by trackball Z-axis: fixed

Press 4D ¡ live reference screen Volume Size (1-3) No. cycles: 2, 3, 4, or 6 (default 4)

Press Full Volume, then Img Store In preview loop, turn Cycle Select knob to select one optimal cycle to avoid stitch artifacts

Press Freeze Press Img Store Press Color: adjust ROI in 2D by trackball, then press 4D If real-time: adjust Volume Size, then press Img Store If full-volume: adjust Volume Size, Num. Cycles, press 4D CF Prepare X-,Y-axis: in 2D, before pressing 4D Z-axis: fixed

Acquire/Reject/Save: the same as full-volume mode TGC, Time gain compensation; LGC, longitudinal gain compensation; 2D, 2-dimensional; 3D, 3-dimensional; 4D, 4-dimensional.


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Figure 4 Cropping methods: An X-Y-Z box crop (A) from the 6-rectangular planes, the active moving plane highlighted (arrow), and an arbitrary plane crop (B) from a single arbitrary plane (purple, arrow). The 9 parallel slices are displayed in horizontal (C) or vertical planes (D, Vivid7 only). Color figure online.

Figure 6 3D image rendering options in the Vivid7 (GE): Low “4D gain” looks 2D-like; turning it up can give the sense of distance, but too much “4D gain” causes dropout. The volume optimization key controls the image processing of brightness (or shading), temporal filtering (smoothness), and grayscale correction (gamma) with 5 preset values. “UD Clarity” controls spatial filtering and edge enhancement, as well as crispness. Color figure online.

Figure 5 3D image rendering options for the iE33 (Philips): High gain makes the image 2D-like, and lower gain reveals deeper tissue; high compression makes the image transparent, and low compression makes the image more solid. Color figure online.

the Vivid7) (Figures 5 and 6). Other postprocessing tips can be found for each echocardiography system (Table 9). Opacification is optimized by the compress button on the iE33, which determines how solid or transparent the volume is; like a compression curve, the gamma button on the Vivid7 corrects grayscales by amplifying certain gray levels over others. There are other threshold controls on the iE33 system, such as brightness, smoothing, and 3D vision control—visions F, G, and H are highest in resolution. Comparatively, the Vivid7 system under “Volume Optimize” offers 5 general sets of default values for brightness, temporal filtering (or smoothness), and grayscale correction (gamma), each of which is also independently adjustable. The “UD Clarity” button controls spatial filtering, edge enhancement, smoothness, and crispness. 4D color vision selections offer various color maps—vision “Depth Enc. bronze/blue” improves depth perception with 2 different colors, which is similar to 3D vision H on the iE33. One of the unique viewing parameters on the Vivid7 is stereoscopic vision, which displays a single volume by overlaying 2 different colors, each from a slightly different viewing angle; to see the stereo effect special glasses are required.

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Table 9 Postprocessing: Image rendering

Cropping Box

Arbitrary plane

Reset Imaging tips Live 3D 3D zoom full-volume

3D Color

Save

iE33 Philips Medical Systems

Vivid7 GE Healthcare

Turn Crop Adjust knob to Box, turn Select Plane knob to highlight the active plane (red, blue, or green), and then turn the Adjust Plane knob to move; Crop Adjust off Turn Crop Adjust knob to Plane, move the plane by trackball or by Plane Adjust, press Retain Crop

Press Box, turn Box Sides knob to choose active plane (red and blue), turning the corresponding knob to move, then press Box Exit to keep; Crop will remove the prior box crop Press Crop, rotate/translate the active cut-plane by trackball or Transl knob, press Set to apply, Crop Exit to keep Press Clear 2D gain: 0-4 dB(⫺30 to 30) 4D gain: mid-range Volume optimize: mid-range (1-5) -Shading (1-4) -Smoothness (1-5) -Gamma (1-7) UD Clarity: mid-range (1-4) 4D Color: Depth Enc. bronze/blue bronze/red Magnify: HR zoom Cine rotate Tissue transparency: 4 (1-10) Flow transparency: 6 (1-13) Color gain: mid-range Baseline shift 6 Slices Press Img Store

Press Reset Cropping Gain: 50% (0-100) Compress: 50 dB (0-100) Bright: 40 (0-100) XRes: On (On/Off) Smoothing: 5 (0-9) 3D Vision: H (A-H) Chroma Map: 2 (off, 1-8) Magnify: 1.0 (0.5-4.0) Rotation (Absolute, Relative) 3D Swivel B/W suppress, Color suppress Color gain: 50% (0-100) Color smoothing: 0 (0-5) Color Vision: A (A-C) Baseline shift Press Create Subpage

2D, Two-dimensional; 3D, three-dimensional; 4D, 4-dimensional.

Once a cropped and optimized 3D image is made, one displays the images. There are many display modes, such as a volume-rendered image, surface-rendered image, wire-frame display, and multiplanar reformatting (MPR) slice display. There is no consensus on how to best display 3D images as of yet. The rendered volume can be presented from various perspectives. For example, in viewing the mitral valve, the LA view is useful, being the same as the surgeon’s view (Figure 7A). Three simultaneous orthogonal (or arbitrary angle) 2D-like slices can be presented in MPR mode (iE33) or Slice mode (Vivid7). Nine parallel slice planes are MPR views in iE33 with horizontal uniformly spaced planes (Figure 4C); the Vivid7 defines the range of the VOI with 2 arbitrary parallel planes (top and bottom) and then presents 7 more uniformly spaced slices between those boundary planes (Figure 4D). On-Cart Analysis An important advantage of 3D is the ability to measure the object in arbitrary orientations without geometric assumptions. On-cart analysis of acquired volumetric data uses a software system such as QLAB version 6.0 (Philips Medical Systems, Andover, MA) on the iE33, EchoPAC 2008 (GE Healthcare, Wauwatosa, WI) and TomTec LV analysis (TomTec Imaging Systems, GmbH) on Vivid7 ultrasound machines. The iE33 QLAB software has 2 options to be used for specific purposes. 1) QLAB-3DQ: By using the MPR mode, which consists of 3 planes (coronal, sagittal, and transverse) and one 3D volume image, it is reasonable to measure an anatomically exact distance and area, especially in the en face view; this has been reported useful in measuring the stenotic mitral valve area (Figure 7B),11,16,29 the noncircular mitral annulus area for continuity equation or proximal isovelocity surface area assessment in mitral regurgitation (Figure 7C),18 and the atrial septal defect area (Figure 7D).19 2) QLAB-3DQAdv: Placing a total of 5 sample dots (4 in mitral annulus and 1 in the apex) in both

end-diastolic and end-systolic frames will make a semiautomatic tracing of the endocardial border of the entire cardiac cycle, which allows assessment of both regional and global LV volume, ejection fraction, and the dyssynchrony index (Figure 8A and B). This analysis can be applied to LA volume measurement using a proper 3D volume image (Figure 9A).8,10 Similarly, Vivid7 EchoPAC software’s Slice mode (comparable to the iE33’s MPR mode) is useful in measuring distance and area. Another on-cart software program is TomTec LV Analysis, which can be applied to cardiac chamber regional and global volumes, as well as dyssynchrony assessment (Figure 8C and D). By using the triplane images from a full-volume image, any cavity volume can be assessed by the same semiautomatic tracing method (end-diastolic and end-systolic), which is useful in volumetric RV assessment (Figure 9B), although it has not been investigated. Pitfalls in Image Acquisition and Analysis Stitch artifacts (Figure 10A). All the ECG-gated, reconstructed images are at risk of stitch artifacts at the interfaces of subvolumes. Artifacts may be caused by an irregular cardiac rhythm, patient motion, and movements of the probe by the operator during acquisition. These can be recognized and managed on the iE33 by observing the final full-volume data in the Y-axis direction and then deciding whether to accept or reject the image, or on the Vivid7 by observing the live reference window and selecting an image cycle that is stitch free. Optimal ECG gating and breath holding are essential to reduce these artifacts, and the operating sonographer must have a steady hand during the entire acquisition. Dropout artifacts (Figure 10B). Acquiring with too low a gain setting or failure to monitor the Z-axis can cause a dropout, omitting a part of the heart; too-high gain can lead to other imaging artifacts. These can be recognized and overcome by


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Figure 7 Rendered 3D full-volume image of the mitral valve demonstrates the anterior mitral valve leaflet flail segment (A2) with ruptured chordae in both the LV view (left, Video 1) and the LA view (surgeon’s view) (right, Video 2) (A). Moving a cropping plane from the LV apex toward the mitral valve leaflet tip shows a rheumatic stenotic morphology of the mitral valve and thickened subvalvular apparatus; the mitral valve area measurement (QLAB-3DQ on the iE33, MPR mode) is displayed (B). A 3D full-volume image in MPR mode shows mitral valve prolapse with severe mitral regurgitation, an example of quantitative measurement of the mitral valve annular area for the continuity equation and the proximal isovelocity surface dimension and vena contracta; note that the mitral annulus diameter we have usually measured in 2D echocardiography (dotted line) and the calculated area from this are not always representing the actual mitral annulus area, and that the vena contracta dimension in 2D can under- or overestimate the severity of mitral regurgitation, in case of noncircular geometry (C). A real-time 3D volumetric image demonstrates a tissue defect between the LA and RA compatible with sinus venosus ASD with anomalous right upper pulmonary vein drainage; ASD en face area measurement is demonstrated (QLAB-3DQ on the iE33, MPR mode) (D). View video clip online. Color figure online. observing the preacquisition real-time view while rotating the volume using the trackball to ensure optimal gain or by optimizing the biplane preview screen images to make sure the VOI is included. Before image acquisition, optimal time gain compensation and longitudinal gain compensation settings are critical, because, unlike overall gain, these settings cannot be changed during the postprocessing. Attenuation artifacts (Figure 10C). Attenuation is a decrement in intensity of a signal along the ultrasound path resulting from

absorption/decreased backscatter, usually seen in the axial axis at long distances, such as basal lateral segments of LV in contrast echocardiography, which affect not only 2D but also the volumetric 3D. Side-lobe artifacts (Figure 10D). Transducer side lobes consist of multiple low-density sounds beams located outside of the main ultrasound beam. Specular side-lobe artifacts occur in proximity to strong, curved, highly reflective surfaces and are similar to the side lobe artifacts seen in 2D echocardiography.

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Figure 8 Analysis of global function, regional volume curves, and asynchrony index (arrow) using QLAB-3DQAdv on the iE33 (upper). First, point to the mitral annulus and apex, at both end-diastolic and end-systolic phases, which leads to semiautomatic border tracing (A); then select “sequence analysis” to get the volumetric results (B, arrow and box) and the intraventricular systolic asynchrony index (B, arrowhead) (Video 3). Analysis of global and regional LV function and asynchrony assessment using TomTec software on the Vivid7 (lower): semiautomatic myocardial tracing in both end-systolic and end-diastolic (C) phases can facilitate analysis of global and regional volume (D) (Video 4). View video clip online. Color figure online.


Figure 10 Stitch artifacts (A, arrows), Dropout artifact of the apical anterolateral wall of the left ventricle (B, arrowheads), attenuation artifact (C, arrowheads), side-lobe artifact (D, arrows). Color figure online.

mode (Vivid7) with an active window having a measuring bar. 2) Make sure the LV is on the right side of the apical 4-chamber image before using semiautomatic segmentation algorithms (QLAB3DQAdv or TomTec LV analysis), because the software is originally designed expecting that orientation for the regional segmental wall interpretation. CONCLUSIONS

Figure 9 An example of volumetric assessment of geographically more challenging anatomic chambers: LA size and function using on-cart QLAB-3DQAdv (iE33) (A), RV size and function using on-cart triplane volume measurement (Vivid7) (B). Color figure online. Pitfalls in 3D color imaging. Both the iE33 system and the Vivid7 have some limitations. The iE33 system with an ⫻3-1 probe does not allow real-time color flow imaging; the Vivid7 does, but only when using a very narrow scan. To optimize the image within the limited angle, make sure the VOI is in the center of the 2D color image before switching to 3D or 4D. In postprocessing, increasing the tissue transparency can help to see the color flow clearly, and changing the color baseline can produce an optimal proximal isovelocity surface area. Pitfalls in 3D volume analysis. 1) Measuring on the displayed 3D volume images itself is inaccurate without proper calibration. Measurement of distance or area needs an MPR display (iE33) or Slice

RT 3D TTE at present complements routine 2D in daily clinical practice by providing additional volumetric information. However, its full complementary potential is not yet exploited. This article is a practical technical operation manual for 3D TTE with current standard echocardiography systems and on-cart software. The details will become obsolete with future systems and software, but once having started clinical 3D echocardiography with a full understanding of basic terminology and menus, one can more easily follow future evolution. In the near future, the ability to acquire a single-heartbeat full-volume scan with higher temporal and spatial resolution, and live 3D color Doppler imaging with a larger angle, should be feasible. Ultimately, perhaps soon, spatial volumetric 3D data will be presented via a 3D display, such as a 3D movie or holographic image, rather than today’s television-like display or crude red-blue stereoscopic visualization. All these will continue to enhance 3D utility and efficiency in daily clinical practice. REFERENCES 1. Dekker DL, Piziali RL, Dong E Jr. A system for ultrasonically imaging the human heart in three dimensions. Comput Biomed Res 1974;7:544-53. 2. von Ramm OT, Smith SW. Real time volumetric ultrasound imaging system. J Digit Imaging 1990;3:261-6.


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