Invasive coronary angiography (ICA) uses harmful x-ray energy. To date, there are no studies evaluating the effect of performing ICA at lower than the standard 15 frames per second (f/s) on radiation dose and image quality. In this study, we investigated the effect of performing ICAs at 7.5 f/s as opposed to the standard 15 f/s on radiation exposure and image quality. Thirty-nine patients referred for ICA for clinical indications were assigned to have their ICA performed at 7.5 f/s or 15 f/s in a 2:1 ratio, respectively. All studies were performed by one experienced operator in the same laboratory. Magnification, table height, collimation, number of images, and specific angles for image acquisition were kept constant to account for these variables that also effect radiation. Studies performed at 7.5 f/s had significantly less radiation exposure than those performed at 15 f/s (252.2 mGy vs 433.7 mGy, p <0.01). In addition, radiation per unit time was also significantly reduced in the 7.5 f/s versus the 15 f/s group (140.0 mGy/min vs 254.7 mGy/min, p <0.01). Image quality was evaluated by an experienced operator blinded to the goals of the study; allstudies were graded as good to excellent. In conclusion, performing ICA at 7.5 f/s versus 15 f/s significantly reduces x-ray exposure without compromising image quality. The results of this single-center study warrant a larger randomized clinical trial.
The quantity of x-ray exposure during invasive coronary angiography (ICA) is directly related to the number of exposures per second, frames per second (f/s) at which ICA is performed. Traditionally ICA was performed at 30 f/s. With advances in imaging techniques and equipment, most operators currently perform ICA at 15 f/s. In this study, we compare radiation exposure and image quality of ICAs performed at 7.5 f/s and 15 f/s.
Methods
From November 25, 2014, to February 13, 2015, 39 consecutive patients referred for ICA were assigned in a 1:2 ratio to have their procedure performed at 15 f/s or 7.5 f/s, respectively. In the 15 f/s arm, both fluoroscopy and cine angiography were performed at 15 f/s. In the 7.5 f/s arm, both fluoroscopy and cine angiography were performed at 7.5 f/s. All studies were performed in the same cardiac catheterization laboratory by one experienced operator to eliminate equipment or interoperator variabilities. All studies were performed from the right femoral approach. Other variables kept constant included table height (maximum), magnification (32), collimation (mostly to heart borders), angulation of the camera as much as possible, number of images, and image acquisition time. To ensure diagnostic adequacy of the study, any and all these variables could be changed at operator’s discretion. All deviations from the previously mentioned variables were collected for comparison between the 2 groups. Other variables collected included age, gender, height, weight, body mass index (BMI), total radiation time, and number of images. Contrast was delivered through ACIST device at preset rates (3 cubic centimeter [cc] per second for a total of 6 cc at pressure per square inch of 210 and rise time of 0.2 seconds for the left coronary artery imaging and 2 cc per second for a total of 4 cc at the same pressure per square inch and rise times for the right coronary imaging). Patients with previous coronary artery bypass surgery, known coronary anomalies, or chronic occlusions with collateralization that required extra images or prolonged image acquisition times were excluded from this study.
At the end of each procedure, the radiation exposure was recorded based on the equipment-displayed measured radiation level. Radiation exposure was measured in mGy as displayed by the equipment. To account for differences in procedure time between the 2 groups, radiation per unit time was also measured in mGy/minute.
All images were evaluated by an experienced angiographer blinded to the goals of the study. The angiographer was asked to grade the quality of images based on the following grading system: (1) good to excellent (defined as more than adequate to make diagnostic interpretation); (2) adequate (defined as adequate to make diagnostic interpretation); and (3) inadequate (defined as inadequate to make diagnostic interpretation). Images from a study were considered to be inadequate if any of the following conditions were met: (1) inability to see all segments of the main coronary arteries (left main, left anterior descending, circumflex, and right coronary artery); (2) inability to estimate the size of the main coronary arteries and their main branches (≥2 mm); (3) inability to estimate degree of severity of blockages in the coronary arteries and their main branches (≥2 mm), if present; and (4) inability to diagnose coronary anomalies or collateral flows, if present. If a study was graded as inadequate image quality, specific reasons for inadequacy of the study were to be stated by the blinded reader. These included any of the previously stated reasons or other reason not stated previously.
Summary statistics (means, SD, medians, minimum and maximum values, and frequency distribution) were generated for patients’ demographic and baseline clinical information and outcome of interest by randomization arm. Graphical displays (box plots and histograms) were used to facilitate the visualization of variable distribution. The primary end point of radiation exposure was compared between the 2 groups based on the Student t test.
The quality of images was graded by an experienced angiographer blinded to the goals of the study. For the purposes of this proof of concept trial, it was decided that the percentage of studies in the 7.5 f/s arm graded as adequate to excellent should be equal to or greater than those in the 15 f/s arm for the 7.5 f/s images to be considered to be of similar quality to the 15 f/s images.
Results
In this study, 39 patients were assigned to 7.5 versus 15 f/s protocols with 2:1 ratio, respectively. The baseline characteristics are depicted in Table 1 . The subjects in the 7.5 f/s arm were younger and had higher body mass and similar BMI compared with those in the 15 f/s arm.
| Variables | 15 frames per second | 7.5 frames per second |
|---|---|---|
| Age (years) | 64.3 | 60.3 |
| Men | 92.3 | 100.0 |
| Weight (lbs.) | 193.4 | 213.2 |
| BMI (kg/m 2 ) | 30.4 | 30.3 |
| Heart rate (beats/min) | 78.2 | 75.6 |
Radiation exposures and procedural variables and deviations are depicted in Table 2 . Total radiation exposure was significantly less in the 7.5 f/s groups as opposed to 15 f/s group (252.2 mGy vs 433.7 mGy, p <0.01). In addition, the average radiation dose per minute was also significantly reduced in the 7.5 f/s group as opposed to the 15 f/s group (140.0 mGy/min vs 254.7 mGy/min). There were no significant differences in total radiation time (1.7 vs 1.8 minutes), number of images per case (6.2 vs 6.1), or volume of contrast used (58 vs 52 ml). There were also no deviations from frame rate or magnification in either group. Of the 26 cases in the 7.5 f/s arm, 3 cases required additional images, and of the 13 cases in the 15 f/s arm, 2 cases required additional images. Image quality was graded as good to excellent, adequate, and inadequate for making diagnostic interpretation. Image quality was graded by an expert angiographer blinded to the goals of the study. As depicted in Table 3 , image quality was graded as good to excellent in all cases in both groups.
| Variables | 15 frames per second | 7.5 frames per second | p-values |
|---|---|---|---|
| Radiation (mGy) | 433.7 | 252.2 | (p<0.01) |
| Radiation time (minutes) | 1.7 | 1.8 | NS |
| Radiation/time (mGy/min) | 254.7 | 140.0 | (p<0.01) |
| Number of image sequences | 6.1 | 6.2 | NS |
| Deviation from frame rate | 0 | 0 | NS |
| Deviation from number of image sequences | 2 | 3 | NS |
| Contrast used (ml) | 58.5 | 52.2 | NS |
| Deviation from magnification | 0 | 0 | NS |
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