CARDIAC CATH LAB EQUIPMENTS

X-Ray Generators:- 

The X-Ray generator produces X-Rays when an electrical current is applied to it. The X-Ray generator could be a device that acts because of the primary control mechanism for the whole fluoroscope. It’s through the X-Ray generator that current is allowed to flow into the thermionic vacuum tube. The fundamental function of adjusting the voltage differential and current of the tube is controlled automatically to keep up optimal contrast and brightness. 

Generator types utilized in fluoroscopy include single phase, three phases, constant potential, and high frequency. High-frequency generators provide superior exposure reproducibility, with the foremost compact size, lowest terms, and lowest repair costs. As a result, high-frequency generators are commonly utilized in new radiographic equipment. X-rays could also be generated in either an eternal or a pulsed mode. Automatic brightness control may be a standard feature of the bulk of contemporary fluoroscopes. Through this method, mA and kVp are constantly monitored and adjusted to optimize the image.  

X-Ray Tube Assembly:-

The majority of x-ray tubes found in current cardiac cath labs contain only two focal spots. The little spot will have a nominal size of 0.5 to 0.6 mm with a kW rating for one exposure of 40 to 50 kW. The big focal spot is going to be 0.9 to 1.2mm in size with a kW rating of 80 to 110 kW. The massive focal spot kW rating should be reasonably matched to the utmost kW of the generator. It’s used for cine or digital image recordings. 

The tiny focal spot is employed primarily for fluoroscopy. The tiny focal spot is additionally the proper choice for cine or digital image recordings of young children. The most common anode diameter provides a 100 mm diameter focal track. This diameter provides an affordable compromise between the specified tube loading and also the delay required to accelerate the anode rotational speed from low speed [approximately 4000 revolutions per minute (rpm)] used during fluoroscopy to high speed (10,000 rpm) used during cine acquisitions. The surface of the anode is usually a tungsten-rhenium alloy; the rhenium is added to smooth the surface of the anode and to cut back the loss of radiation output. 

The body of the anode is sometimes graphite, which increases the warmth energy that can be stored without damage thanks to increases in temperature. The specified small anode angle could be a compromise between field coverage and the warmth capacity rating of the tube. A minimum of a 9-degree angle is important to hide a 9-inch field of view (FoV) image intensifier at a Source Image Receptor Distance (SID) of 30 inches. 

The anode chilling rate should be a minimum of 400,000 heat units per minute (HU/min). Units with medium to large workloads should be equipped with circulating liquid (oil or water) heat exchangers to more efficiently and quickly convey heat from the anode body of the encircling atmosphere outside the tube. This exchanger typically quite doubles the warmth dissipation rate of a fan-cooled housing which is often 100,000 HU/min. This accelerated cooling allows the cardiologist to continue the case, mixing fluoroscopy with cine acquisitions without a forced delay. 

Tube Stand:-

The tube stand supports both the electron tube housing with the collimator and therefore the image intensifier with the imaging chain. It’s designed to keep up the alignment of the central ray for the x-ray beam to the middle of the image intensifier while the angle of the central ray changes within either the coronal or transverse plane of the patient’s body. This cranial-caudal or lateral rotation of the X-ray tube and image intensifier provides the required compound imaging angles required to minimize superposition within the image of the tortuous coronary arteries. 

The cardiologist places the anatomy of interest at the intersection of the 2 orthogonal rotations, the isocenter, to forestall the movement of the anatomy across the FoV of the image when the compound angles are adjusted. Translational movement of the image intensifier parallel to the central ray is accomplished by providing a variable focal spot-to-image receptor distance (SID) of a minimum of 90 to 120 centimeters (cm). 

This enables the positioning of the input plane of the image intensifier near the exit plane of the patient no matter the patient's thickness or compound angle to reduce magnification and geometric unsharpness within the image. The stand should provide extra movement (e.g. Rotation about its floor or ceiling support) to permit the equipment to be quickly removed from the vicinity of the patient when emergency access is required. Collision guards or slip clutches are provided to forestall further power-driven motion of the stand upon contact with the patient or other stationary objects.

Patient Table:-

Floor-mounted special procedure table tops in cath labs are typically supported by a pedestal base with motorized vertical motion sufficient to position any part of the patient’s body at the vertical isocenter of the imaging plane. The tabletop should be wide enough to support the patient, but narrow enough to permit the positioning of the image intensifier adjacent to the exit plane of the patient during lateral imaging. 

The length of the table must be sufficient to comfortably support a tall adult, with some additional room. The composition of the many tabletops is often carbon fiber material. This composition provides the strength required to support a minimum of a 350-pound patient cantilevered from the pedestal support while minimizing the attenuation of the diagnostic x-ray. The tabletop must “float” with regard to the pedestal when electromagnets are released to permit axial and transverse motion of the tabletop relative to the isocenter of the imaging equipment. The longitudinal and transverse motion of the tabletop respectively should be at least 100 cm and 30 cm

Control Console:-

The control console for a cine system should have the flexibility to pick both fluoroscopic and cine technique factors. For fluoroscopic operations, there should be selection switches to vary from continuous to pulsed fluoroscopy. Pulsed fluoroscopy should be available from 30 pulses per second to a minimum of 7. 5 pulses per second. For all modes, the utilized kVp and mA should be displayed on an easy-to-read display indicator. Moreover, the cumulative fluoroscopy time should be displayed and a “5-minute (of elapsed fluoroscopy time) buzzer” should clearly be heard in both the procedure room and also the control booth. It’s also helpful to own a fluoroscopic lock switch that may “hold” a specific combination of “kVp/mA.” 

The utilized FoV of the image intensifier should even be clearly displayed on the control console. Some units allow manual selection of kVp/mA during fluoroscopy additionally to the Automatic Brightness Control (ABC) of fluoroscopy. The cine controls typically have a gaggle of pre-established programs from which to pick appropriate technique factors. In general, cine frame rates from 15 to 60 fps should be available. Adult cardiac cine is typically performed at 30 fps and pediatric frame rates range from 30 to 60 fps cine pulse widths are typically 2 to 10 msec. The X-ray tube potentials should start above 60 kVp so as to limit the patient radiation dose and may go up to 120 kVp. Cine tube current values generally range from 50 to 800 mA. 

The ABC system automatically adjusts some combination of kVp, mA, and pulse width during cine operation to take care of the appropriate image quality. For cine, there should be several pre-programmed technique factors using different frame rates, starting kVps, starting pulse widths, and cine run durations. The control console should, at a minimum, display the cine kVp and mA(s) on an easy-to-read alphanumeric display. The sunshine levels exiting the image intensifier could also be indicated during cine filming as a relative check of proper cine film exposure. There should even be a button to mechanically advance the cine film (“jog” button). 

Finally, the control console should have an indicator to indicate the amount of film left within the cine film magazine. Digital imaging systems need similar function-related buttons. There should even be an “x-ray on” indicator and/or a door interlock indicator.

Grids:-

Cardiac imaging often employs lateral oblique projections that attenuate the x-ray beam and produce a big number of scattered photons. The scattered photons tend to scale back the contrast of coronary arteries and obscure the visualization of smaller arterial vessels and branches. Hence, the utilization of appropriate grid(s) to get rid of much of the scattered radiation leads to a contrast improvement and a capability to work out smaller vessel sizes. The usage of grids may lead to a rise in radiation dose to the patient by an element of two to 4 times. 

The best grid would offer a high percentage of primary radiation transmission and a high percentage of scatter radiation attenuation. The grid should be circular in shape so as to properly fit the image intensifier and to make sure the alignment to the central ray of the x-ray beam is necessary to forestall the grid cut-off of primary photons. Usually, carbon fiber interspace material is used so as to enhance primary radiation transmission. 

Although parallel and crossed grids are employed in the past for cardiac studies, the foremost common grid for these studies may be a focused grid. So as to accommodate a spread of SIDs, low grid ratios are utilized. Typically, grid ratios of 4:1 up to 8:1 are used. The focal length of the grid depends upon the x-ray tube/image intensifier mechanical web being used. 

Modern cardiac imaging systems typically have the capability to vary the SID from 80 cm up to 120 cm. The grids should have a usable focal range that accommodates these variations. It’s important to possess the grid lines mounted perpendicular to the TV raster lines to avoid interference patterns. Because the grids are stationary, thick grid lines would obscure small vessels. 

Therefore, thin grid lines with a high number of lines per inch are usually employed. Finally, there should be a mechanism to simply remove grids for physics/x-ray service test procedures. This feature also allows the removal of the grid by the operator when air gap techniques are wont to geometrically magnify the pediatric patient’s small anatomy within the image.

Television System:-

Digital recording of fluoro and cine images is usually taken from the television System. Hence, the television system should be designed to provide appropriate image quality for these studies. Foremost, the television system for cardiac studies should exhibit minimal persistence of the images so that frame rates up to 60 fps can be accommodated. This feature is termed minimal lag and must be measured with a dynamic test, such as the spinning spoke patterns.

Digital Imaging Systems:-

The challenge with digital imaging is the sheer volume of digital data. Typical diagnostic cardiac catheterization procedures in adults involve the imaging of 5 to 10 runs of a 6 to 7-second duration each with 30 fps. Thus, each patient study contains 2000 or more images. The minimum specifications of a 512 × 512 matrix and a pixel depth of 1 to 1.5 Bytes (8 to 12 bits) to capture the transmitted x-ray intensity data result in each image and also the entire study containing about 0.25 to 0.39 and 500 to 750 Megabytes (MB) of information, respectively. 

While the improved spatial resolution of 1024 × 1024 matrix is preferred, the larger matrix size has the disadvantages of increased quantum mottle and/or radiation dose to the patient still the maximum amount larger data rates and total image data. The info acquisition rates for a 512 × 512 matrix are typically 7.5 to 12 MB per second which is adequate for 60 to 90 MHz; for the 1024 ×1024 matrix, the information rates would be fourfold greater. Bi-Plane Cardiac Cath systems double the information acquisition rates that will be handled. 

For these reasons, most current equipment utilizes the 1024 × 1024 matrix only at lower frame rates of imaging; whereas, the 512 × 512 matrix is routinely used for many clinical studies. The spatial resolution of digital systems is set by the image acquisition equipment (e.g., video system), the matrix size, and therefore the image intensifier FoV. Generally, the calculated spatial resolution is capable of half the matrix size/FoV in millimeters. For a 512 × 512 matrix with a 150 mm FoV, the calculated spatial resolution would be about 1.7 LP/mm. The 1024 × 1024 matrix size would increase the spatial resolution to about 2.5 to 3.0 LP/mm. while these values for spatial resolution are but cine film imaging, digital systems have improved dynamic range, image processing capabilities, noise suppression, and networking and have image storage/display advantages. 

Hence, many cardiac cath labs are utilizing digital cine image acquisition. Most current digital cine imaging is completed by digitizing the video signal from a high-quality camera. The analog signal from a piece of television equipment goes to a data converter (ADC) and so it’s transmitted to the digital storage buffer for temporary storage. In the future, one can expect analog television cameras to get replaced by CCDs which will directly acquire the image as a digital image. Moreover, the image intensifier and TV camera are also replaced by a right away radiation detector/imaging system in a very few more years; such systems are currently under development and testing.

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