Fluoroscopy Screen Parameters in the Cath Lab: A Complete Guide for Cardiologists and Electrophysiologists

Have a look on his example fluoroscopy screen of Philips cath lab/fluoroscopy monitor during coronary angiography (CAG). Here's what the displayed parameters mean:

Display Meaning

CAG 15 f/s Coronary angiography at 15 frames/second (cine acquisition). Higher frame rate = smoother motion but higher radiation.

LAO/RAO: 0° No Left Anterior Oblique or Right Anterior Oblique angulation. Straight AP view.

CRA/CAU: 0° No cranial or caudal tilt. AP projection.

SID: 95 cm Source-to-Image Distance = distance from X-ray tube focal spot to detector.

8" Field of view (FOV) is 8 inches. Smaller FOV provides magnification and better spatial resolution.

0° (rotation icon) Detector rotation is neutral.

89 cm Table height (approximately detector/patient positioning parameter).

38 cm Detector position or source-to-patient distance parameter (machine dependent).

1° Slight detector/head tilt.

0% Image processing/roadmap or contrast enhancement parameter (vendor-specific).

Eye icon + L LIH (Last Image Hold) is active. The displayed image is the last acquired fluoroscopic frame.

5.0 min Total fluoroscopy time during the procedure so far.

Exposure parameters (bottom)

Fluoroscopy (F)

80 kV = Tube voltage

20 mA = Tube current

3.3 ms = Pulse width/exposure time per pulse

Radiography/Cine (R)

73 kV

173 mA

3.2 ms

Notice that cine uses much higher tube current (173 mA vs 20 mA), which is why cine images have better quality but deliver a higher radiation dose.

Orientation markers

LIH = Last Image Hold

L = Left side of the patient

Warning message

> "Init setting of collimator required. Call service."

This indicates the system believes the collimator requires initialization or calibration. It is generally a service/maintenance message and should be evaluated by the equipment engineer if it persists. It does not necessarily mean the current procedure cannot continue, but the collimator may not be functioning optimally.

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Understanding Fluoroscopy Screen Parameters in the Cath Lab: A Complete Guide for Cardiologists and Electrophysiologists

Whether you are performing coronary angiography, pacemaker implantation, CRT, ICD procedures, or catheter ablation, understanding every parameter displayed on the fluoroscopy monitor is essential. These values directly affect image quality, radiation exposure, procedural efficiency, and patient safety.

This guide explains the common fluoroscopy screen parameters seen on modern cath lab systems.

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1. LIH (Last Image Hold)

Definition

Last Image Hold (LIH) is the last fluoroscopic image displayed after you release the fluoroscopy pedal.

Purpose

Reduces radiation exposure

Allows catheter position review without additional X-rays

Helps plan the next catheter movement

Improves procedural efficiency

Key Point

No new radiation is generated while reviewing an LIH image.

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2. CAG 15 f/s

Meaning

Coronary Angiography recorded at 15 frames per second.

The machine acquires 15 individual images every second during cine recording.

Common frame rates include:

7.5 fps

10 fps

15 fps

30 fps (rare today)

Higher frame rate

Advantages

Better temporal resolution

Smoother visualization of moving catheters

Improved coronary imaging

Disadvantages

Increased radiation dose

Larger storage requirements

Current recommendations

Routine coronary angiography:

10–15 fps

Electrophysiology procedures:

7.5 fps is usually sufficient

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3. LAO / RAO

Left Anterior Oblique / Right Anterior Oblique Angulation

These represent horizontal rotation of the C-arm around the patient.

Examples

LAO 45°

The X-ray tube rotates toward the patient's left.

RAO 30°

The tube rotates toward the patient's right.

Why important?

Different angulations separate overlapping cardiac structures.

Examples

Coronary angiography

LAO Cranial → Left main bifurcation

RAO Caudal → Circumflex artery

LAO Caudal → Spider view

Electrophysiology

LAO 45° differentiates septal vs lateral structures

RAO 30° assesses anterior-posterior catheter position

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4. Cranial (CRA) / Caudal (CAU)

These indicate vertical tilt of the C-arm.

Cranial

The X-ray beam points toward the patient's head.

Caudal

The beam points toward the feet.

Uses

Coronary imaging

Cranial views elongate LAD

Caudal views visualize circumflex and left main

Electrophysiology

Useful for

Coronary sinus lead positioning

His bundle localization

Left bundle branch pacing

Septal visualization

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5. SID (Source-to-Image Distance)

Definition

Distance between the X-ray tube focal spot and the detector.

Example

95 cm

Effects

Increasing SID

Advantages

Reduced geometric magnification

Better image sharpness

Disadvantages

May require higher radiation output

Modern systems automatically compensate.

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6. Field of View (FOV)

Example

8-inch field

Field of View determines the size of anatomy displayed.

Common sizes

6 inch

8 inch

10 inch

12 inch

Smaller field

Advantages

Higher magnification

Better spatial resolution

Disadvantages

Higher patient radiation

Smaller visible area

Larger field

Advantages

Wider anatomy

Lower magnification

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7. Fluoroscopy Time

Example

5.0 minutes

This is the cumulative duration during which fluoroscopy has been active.

Important

Fluoroscopy time alone does not accurately represent radiation dose.

Two procedures with identical fluoroscopy times may deliver very different doses depending on:

Patient size

Pulse rate

Frame rate

Magnification

Angulation

Dose settings

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8. Tube Voltage (kV)

Example

80 kV

kV determines X-ray energy.

Higher kV

Advantages

Better penetration

Lower image noise

Disadvantages

Reduced image contrast

Lower kV

Advantages

Better contrast

Disadvantages

Less penetration

Higher patient dose in large individuals

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9. Tube Current (mA)

Example

20 mA (Fluoroscopy)

173 mA (Cine)

mA determines the number of X-ray photons produced.

Higher mA

Advantages

Better image quality

Less noise

Disadvantages

Increased radiation dose

Notice that cine acquisition uses much higher mA than fluoroscopy because high-quality images are required for permanent recording.

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10. Pulse Width (ms)

Example

3.3 milliseconds

Pulse width is the duration of each X-ray pulse.

Short pulse width

Advantages

Less motion blur

Sharper catheter visualization

Long pulse width

Advantages

More photons

Less image noise

Disadvantages

More motion blur

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11. Fluoroscopy (F)

Displayed as

F

Represents live, low-dose continuous or pulsed imaging.

Characteristics

Lowest radiation mode

Used for catheter manipulation

Not intended for permanent storage

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12. Cine (R)

Displayed as

R

Represents recorded radiographic acquisition.

Characteristics

High image quality

Higher radiation dose

Permanently stored

Used for coronary angiography and documentation

Radiation during cine may be 5–10 times higher than during fluoroscopy, depending on system settings.

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13. Detector Rotation

Some systems display detector rotational angle.

This indicates detector orientation relative to the patient.

Used for

Optimizing visualization

Reducing overlap

Improving procedural ergonomics

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14. Table Height

Example

89 cm

Represents patient table position.

Proper table height

Improves operator ergonomics

Reduces radiation scatter

Optimizes image quality

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15. Detector Position

Some systems display detector distance from the patient.

General rule

Keep the detector as close to the patient as possible.

Benefits

Lower radiation dose

Better image quality

Less magnification distortion

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16. Dose Area Product (DAP/KAP)

Although not shown in your image, this is one of the most important radiation parameters.

Definition

DAP (or Kerma Area Product, KAP) is the total X-ray energy delivered multiplied by the irradiated area.

Unit

Gy·cm²

Uses

Estimates stochastic radiation risk

Tracks cumulative radiation exposure

Required for quality assurance

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17. Air Kerma (AK)

Usually displayed separately.

Definition

Radiation delivered to a reference point near the patient's skin.

Unit

Gray (Gy)

Importance

Air Kerma correlates with the risk of skin injury.

Clinical thresholds

≥2 Gy: Increased awareness

≥5 Gy: Follow-up recommended

≥10 Gy: Significant risk of deterministic skin injury

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18. Collimator Warning

Example

"Init setting of collimator required. Call service."

Meaning

The collimator requires initialization or calibration.

Possible causes

System startup issue

Mechanical calibration error

Service requirement

If persistent, biomedical engineering or the equipment vendor should evaluate the system.

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Radiation Reduction Tips for Every Procedure

Use LIH instead of repeated fluoroscopy.

Prefer 7.5 fps for most electrophysiology procedures.

Keep the detector close to the patient.

Maximize the distance between the X-ray tube and the patient.

Use tight collimation.

Avoid unnecessary cine acquisitions.

Use lower magnification whenever possible.

Minimize steep LAO/cranial projections, which often require higher radiation output.

Wear appropriate shielding and monitor operator radiation exposure.

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Key Takeaway

Every number displayed on the fluoroscopy monitor has a practical impact on image quality, radiation dose, and procedural success. A clear understanding of parameters such as LIH, frame rate, LAO/RAO, cranial/caudal angulation, SID, field of view, fluoroscopy time, kV, mA, pulse width, DAP, and Air Kerma enables cardiologists and electrophysiologists to optimize imaging while adhering to the ALARA (As Low As Reasonably Achievable) principle for radiation safety.

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