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Long Length Imaging: An Alternative to Image Stitching

Lower limb malformations, scoliosis, and other spinal column structural problems rely on full length diagnostic imaging studies to identify disease and inform treatment. Acquiring spatially accurate full-length images in a timely manner on the entire spine or lower limb from hip to ankle has been an ongoing challenge for orthopedic providers. The most common options for diagnostic x-ray imaging in these cases have been conventional digital radiology (DR) or computed radiology (CR) imaging systems.  Both of these approaches are often less than satisfactory due to long exam times and study repeats due to patient motion. These shortcomings have contributed to the introduction of large format or leg length imaging (LLi) DR detectors to the marketplace.

Large format imaging detectors offer significant new advantages for clinicians looking to improve patient outcomes while increasing their practice’s patient throughput efficiency. These detectors represent the newest option for clinicians looking to overcome the challenges of spinal and long leg (LLi) imaging studies. Thanks to the progression of technology in this field, large format x-ray detector manufacturers can combine the practical benefits of existing technologies to provide practices with a more efficient and effective option. 

doctor handshake with a patient at doctors bright modern office in hospital

The First Generation: CR Detectors

The need for x-ray imaging studies on large areas of anatomy has been addressed over time with two different types of detector systems. The first option for clinicians looking to capture full spine or leg images utilized multiple CR detectors. The standard method of taking long leg or full spine images with a CR system is to use three 14x17” CR cassettes arranged in a long format cassette housing positioned behind the patient to cover the total area of the anatomy being imaged. Once the CR cassette housing is in place, a single x-ray exposure is made.  The three individual cassettes are then processed through a CR cassette reader and the images are stitched together to form a single projection of the large format anatomy of interest.  One advantage to this approach is that it requires only a single exposure from the X-ray system to produce the large format image.  

In addition to the single exposure benefit, using the three CR cassettes simultaneously greatly reduces the need to retake images due to patient motion. These benefits of large format imaging with CR detectors have induced some facilities to continue to use this method for all their large format imaging, despite having converted to DR technology for the remainder of their x-ray exams. This requires that the facility maintain both CR and DR systems concurrently in regard to costly repairs and updates.

Unfortunately, utilizing CR systems for large format imaging is very inefficient due to long exam times.  It can take 20 to 25 minutes to assemble and disassemble the cassettes, complete an exposure, feed the cassettes into the CR reader, and finally stitch the images together. The ongoing maintenance of a large format CR solution can also be costly due to repairs needed on cassettes, cassette housings and the CR cassette reader.   Additionally, Medicare reimbursements are also gradually fading for this type of detector in hopes that practitioners will move to DR detectors.

The Second Generation: Conventional Sized Digital Radiography (DR) Detectors

The most widely used technology for long-leg or spinal studies today are DR detector systems, which were first introduced in 1987. Unlike CR detectors, the images from DR detectors do not need to be processed through a reader and instead can be viewed seconds after the detector is exposed.  DR detectors are typically 14” x17” or 17” x 17” in dimension. However, DR detectors do not normally allow users to stack multiple panels to capture a large format image simultaneously. The process for acquiring a large format image study with conventional DR detectors involves taking either two or three sequential exposures (depending on the size of the anatomy of interest) and then stitching these images together to form a single large format image.  In between each exposure, the X-ray technician must reposition both the detector and the X-ray tube head to acquire the next segment of anatomy.   While this can be faster than large format CR imaging, it is very prone to having patient motion occur between image captures leading to repeat studies.   This increases total patient X-ray dose and exam times, both being very undesirable outcomes.

Additionally, spatial accuracy of the final image is often a concern for providers since images are overlapped and then stitched after all the exposures are completed.  This can often lead to imperfect alignment and therefore spatial accuracy of the anatomy in question.

The New Generation: Large format (LLi) Imaging Detectors

Clinicians can eliminate the significant disadvantages of both CR and conventional DR large format studies with the addition of a large format DR detector to their imaging suite.  

One example of a large format detector is the Cuattro ONE.  A single exposure utilizing the Cuattro ONE produces a 17" x 51" field of view with a preview image available in six seconds and a fully processed view available in twelve seconds.  Cuattro ONE also allows the user to isolate the top, middle or bottom portions of the detector in order to perform 17" x 17" conventional weight bearing studies.  

Also available for large format imaging, the recently introduced Cuattro ONEm is a 17” x 34” wireless detector suitable for full spine and portable large format imaging studies.  ONEm can also be coupled with qualifying 14” x 17” wireless detectors to provide up to 50” field of view for long leg (LLi) studies as needed.

Since long length imaging detectors don’t require sequential image stitching, they address the spatial accuracy problems associated with conventional DR large format studies. Compared to conventional DR detector systems which take between 10-12 minutes to complete a study and CR systems which can take between 20 and 25 minutes, large format detector systems can complete these studies in 1 to 2 minutes. The single exposure also reduces the total radiation dose exposure to both patients and staff when compared to the older system types.

Simplifying the completion of these challenging large format exams allows clinicians to quickly and easily capture and review all the relevant anatomy in these clinical situations.   This new technological approach can significantly improve patient outcomes by assessing the entire anatomy of interest rather than segmental areas only (as an example, a patient with significant lumbar spine disease may also have clinically relevant thoracic or cervical spinal changes that can only be identified if the entire spinal column is evaluated).   Patients needing spinal intervention surgery benefit from better and more comprehensive x-ray imaging since these studies can identify undetected issues in other areas of the spine. This leads to a faster diagnosis of other issues and allows them to also be treated with consideration to the current complaints.


The progression of x-ray imaging technology allows clinicians to continue improving their patients’ outcomes. Long leg studies and full spine imaging have been challenging to accomplish with current technology. However, the introduction of large format (LLi) detectors to the market addresses the problems associated with CR and DR detector systems when performing these exams. As awareness grows about these kinds of x-ray detectors, clinicians will be able to see more patients while providing them with a higher standard of care.