8.2 Ultrasound, IVUS, OCT & ICE Equipment

Ultrasound, IVUS, OCT & ICE Equipment

Outline Image Production 1.C is procedural imaging equipment. The CI technologist needs basic knowledge and operation of the ultrasound unit, intravascular ultrasound (IVUS), optical coherence tomography (OCT), and intracardiac echocardiography (ICE). This is not the procedures chapter on every plaque subtype. It is whether you can set up the box, which physics you are using, and which modality requires a blood-free field.

Quick Answer: Access ultrasound uses a linear probe, compressibility, and color Doppler. IVUS images plaque and stents from inside the vessel without clearing blood. OCT uses near-infrared light, has about 10× the spatial resolution of IVUS, and requires a contrast or saline flush. ICE sits in the right atrium, usually from a femoral vein, for structural and EP work without TEE's esophageal risk.

Vascular ultrasound unit (access)

The cart in the room is a diagnostic ultrasound system. For femoral, radial, and jugular access the default transducer is a high-frequency linear probe (often about 7–15 MHz). High frequency gives resolution in superficial vessels. A low-frequency curvilinear probe is abdominal equipment you are not using as the default at the wrist.

Operation. Gel on the skin; a sterile probe cover and sterile gel once the field is up. Set depth so the vessel fills the middle of the screen, focus at the vessel, and gain so the lumen is dark and the walls are visible. Keep the color box small — a huge box tanks frame rate.

Compressibility distinguishes vein from artery: the vein collapses with probe pressure; the artery is pulsatile and resists. Color Doppler (and pulse-wave if needed) shows direction: a triphasic or biphasic arterial waveform versus continuous or respirophasic venous flow. In the groin, mark the common femoral artery (CFA) bifurcation before the stick; the vein is typically medial. A bare probe on a sterile groin is a break in technique, not a time-saver.

Trap: turning color on does not replace compression. Calcified plaque can make an artery feel stiff; still look for pulsatility and Doppler rather than guessing.

IVUS: ultrasound on a catheter

An IVUS catheter carries a miniaturized ultrasound transducer — a mechanical rotating element or a solid-state phased array. Coronary catheters commonly run about 20–45 MHz; lower-frequency catheters exist for large peripheral vessels. It is advanced over a coronary wire, usually after anticoagulation, and pulled back through the lesion (manual or motorized pullback).

Physics. Ultrasound reflects at tissue interfaces. At coronary IVUS frequencies, blood is a speckle-filled lumen. You do not need to displace blood. That is the operational advantage over OCT: IVUS works in a flowing, blood-filled artery.

Gray-scale picture. Lumen, vessel wall, plaque (soft, fibrous, calcified with acoustic shadowing), and stent struts as bright points. Measurements the operator uses: minimum lumen area (MLA), reference lumen areas, plaque burden, and after PCI stent expansion and malapposition (struts standing off the wall). The CI technologist boots the console, selects the correct catheter on the system, calibrates per IFU, connects the patient interface, keeps the field sterile, records pullbacks, and archives to the lab's PACS pathway.

Safety. IVUS does not need a contrast flush for imaging, but the catheter still occupies lumen — watch damping, ischemia, and spasm. Do not power-inject an LV-gram through an IVUS catheter that is not rated for it. Flush the IVUS lumen per IFU (some mechanical catheters are saline-filled).

Teaching resolution. Coronary IVUS axial resolution is commonly on the order of 100–200 µm. That is good enough for MLA and most stent-expansion questions, and deep enough to see external elastic membrane in many vessels. It is not OCT-fine for thin-cap or strut-coverage detail.

OCT: near-infrared light, blood must go

OCT uses near-infrared light (typically around 1.3 µm) and interferometry, not sound. Light gives spatial resolution on the order of 10–20 µm, roughly 10× finer than IVUS. The tradeoff is depth: OCT penetration is about 1–2 mm of tissue; IVUS sees several millimeters into plaque. Heavy calcium and red thrombus can also limit OCT.

Blood-free field. Red blood cells scatter near-infrared light. OCT requires a flush — iodinated contrast or, in some protocols, saline — to clear the lumen during a fast automated pullback. That flush is a contrast-volume and ischemia consideration the technologist should announce. No flush, no image.

Why operators pick OCT. Dissection flaps, thrombus, stent-strut coverage, malapposition at a scale IVUS will miss, and calcium thickness for lithotripsy planning. Why they still pick IVUS: left-main and aorto-ostial landmarks, large-vessel depth, CKD when you cannot afford the flush, and any situation where a blood-filled field is safer.

Operation. Console on, catheter primed, wire lumen flushed, contrast injector or manifold ready for the purge, pullback triggered only when the lumen is clear. Same sterility rules as any coronary device. Do not treat OCT as “IVUS with a prettier button.”

ICE: ultrasound from inside the heart

Intracardiac echocardiography (ICE) is a steerable ultrasound catheter, commonly 8–10 Fr, placed in the right atrium (RA). Access is typically femoral venous (sometimes internal jugular). The transducer looks at the interatrial septum, adjacent left atrium, aortic valve, and neighboring structures from inside the blood pool. Like IVUS, ICE is ultrasound, so blood does not have to be cleared.

Typical use — structural and electrophysiology. Transseptal puncture (tenting of the fossa ovalis), atrial septal defect (ASD) or PFO closure, left atrial appendage (LAA) occlusion, adjunctive imaging for transcatheter aortic valve replacement (TAVR), and ablation geometry. The CI technologist prepares the ICE cable and sterile sleeve, connects to the ultrasound unit, selects the ICE preset, and helps the operator steer under combined fluoro and ultrasound. Color Doppler on ICE can show residual ASD or appendage flow — still ultrasound, still no coronary-style flush.

ICE versus transesophageal echocardiography (TEE). TEE images from the esophagus, usually needs anesthesia or deep sedation and an echocardiographer, and carries esophageal injury, aspiration, and probe-intubation risk. ICE is operator-controlled from the table, avoids the esophagus, and still requires venous access, a larger sheath, and anticoagulation awareness. ICE does not automatically replace TEE for every TAVR; it is the cath-lab imaging catheter the outline wants you to know. Do not put ICE in the esophagus on a test question — that is TEE. Do not put ICE in a coronary artery — that is IVUS or OCT.

Modality / physics / blood-free field / typical use

Worked case

Elective PCI in a patient with eGFR 28 mL/min/1.73 m². The operator wants to limit contrast and still confirm stent expansion. IVUS is the equipment that images in a blood-filled lumen and can report MLA and malapposition without an OCT flush. If the same operator later needs to see a suspected edge dissection at strut-level detail and accepts a flush volume, that is OCT. Groin access still starts with a linear probe and compression, not with ICE. If the next case is LAA occlusion with transseptal puncture, roll in ICE — femoral venous, RA — not a coronary OCT catheter and not a default TEE if ICE is the plan.

Exam traps

• Saying OCT works in a blood-filled lumen like IVUS.
• Claiming IVUS has higher spatial resolution than OCT.
• Putting ICE in the esophagus (TEE) or in a coronary (IVUS/OCT).
• Using a curvilinear abdominal probe as the default radial-access transducer.
• Power-injecting an LV-gram through an IVUS or OCT catheter.