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SIGNA™ Pulse of MR

Autumn 2021

Issue Archive

Volume 31 – Autumn 2021

Issue Archive

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Tiron C.M. Pechet, MD

Shields Health Care Group

Boston, MA

SPOTLIGHT

Changing an athlete’s injury diagnosis and management with MR bone imaging technology

Moreover, longitudinal imaging is often used to monitor the healing progress and this additional exposure to CT, X-ray or SPECT further increases a patient’s radiation dose. This is particularly a key concern when evaluating pediatrics and young adults.

oZTEo is a new method of MR bone imaging that provides CT-like images of the bone, available exclusively from GE Healthcare in the SIGNA™Works AIR™ IQ Edition software release. Tiron C.M. Pechet, MD, Assistant Medical Director and Chief Medical Information Officer at Shields Health Care Group, a medical imaging provider with more than 30 locations throughout New England, recently evaluated the impact of oZTEo in MR exams of young elite athletes.

According to Dr. Pechet, examining bone surfaces in detail with conventional MR is difficult due to adjacent signal from soft tissues and marrow, inadequate through-plane (slice) resolution combined with curving surfaces requiring multiple planes for assessment, and other sources of low MR signal or signal loss that can lead to "signal void," which is difficult to distinguish from bone cortex.

"We have become reasonably proficient, or so we thought, at visualizing the lowsignal cortex," Dr. Pechet says. "But now comparing even high-resolution isotropic voxel 3D imaging with 3D oZTEo, it’s easy to see what we have been missing."

What if MR could provide similar bony details as CT? Patients could avoid additional exposure to ionizing radiation and reduce the number of imaging exams or corresponding appointments, therefore, lowering overall their healthcare costs.

Tiron C.M. Pechet, MD

Shields Health Care Group

Boston, MA

oZTEo: a different, valuable type of MR imaging data

oZTEo delivers bone contrast information to the radiologist and referring physician – information that is more difficult to see with another sequence, Dr. Pechet says. And that is exactly why he believes it is so valuable. In his opinion, it is similar to when diffusion MR was first introduced. Diffusion provided a new contrast that had an impact on the diagnosis and treatment of stroke, which led MR imaging providers to add the sequence and associated scan time to routine brain acquisitions in order to provide optimal patient care.

"Under the appropriate circumstances, we need to provide the oZTEo information to the clinician and patient," he adds. "In many cases, using oZTEo will spare the patient the time, radiation exposure, multiple visits and cost."

"We have seen multiple examples in the lumbar spine of pathology that were suspected because of marrow edema on STIR or sclerosis on T1, but the actual fracture was not visible on conventional imaging or even on 3D isotropic voxel Cube imaging," Dr. Pechet explains. "We have tried thin, 2 mm section T1 imaging. Guided by the cortical defect on the oZTEo images, we could go back and find the defect on very thin section T1 images, but confidence remained much higher on the oZTEo sequence. And time of acquisition was similar."

Many athletes/patients receive an X-ray, arthrogram, MR and CT exam for surgical planning purposes. Dr. Pechet believes oZTEo may replace CT especially for surgical planning of the hip and shoulder, which reduces the number of imaging studies a patient must undergo as well as spares them from additional exposure to ionizing radiation.

In fact, a sports medicine physician in the Boston area referred a female gymnast to Shields in an effort to avoid CT because of ionizing radiation. And it’s not just the initial diagnostic study; these young women will undergo follow-up imaging studies to evaluate their healing process. This is where MR with oZTEo can really make a difference in patient care.

"I think it is quite important especially where pelvic radiation is concerned, which is unavoidable when imaging the pelvis with CT for lumbar spine, SI joint and hip pathology," Dr. Pechet says. "I see expanded use for oZTEo in all of those cases. In our experience, we have already seen that CT imaging of spondylolysis is unnecessary if we use oZTEo. I suspect that imaging of the SI joint and of the hip for assessment of femoroacetabular impingement (FAI) as well as the shoulder will follow."

It is not that CT isn’t a valuable imaging study, Dr. Pechet continues. Rather, the use of oZTEo will enable physicians to reprioritize their use of CT. Dr. Pechet suggests that in young athletes where MR imaging is indicated, MR with oZTEo should be acquired prior to CT, potentially eliminating the need for another imaging study altogether.

"More importantly, oZTEo gives us a chance to make diagnoses that were challenging or impossible to make with conventional MR imaging," Dr. Pechet adds. "It’s often the case that you can suspect or infer the presence of a fracture based on edema within the marrow on fluid-sensitive imaging, but our confidence is much higher when we can visualize the fracture using oZTEo."

oZTEo is a relatively motion-insensitive sequence because it is based on a radial acquisition of k-space, similar to PROPELLER. Since it a 3D sequence, it can be acquired in the most efficient plane and reformatted into any plane to visualize the pathology.

"Adding oZTEo to 3D T2 Cube or STIR acquisition is a powerful tool to assess both the osseus and soft tissue pathology, which are easily co-registered," says Dr. Pechet.

Co-registration is important to understand the relationship of the soft tissue and marrow signal changes with respect to the osseus, or bone, pathology to assess whether the edema corresponds to the actual site of the fracture (acute fracture) or if it is close to but not at the bony injury site, and therefore more likely represents stress response and a chronic fracture. oZTEo also shows bony sclerosis well.

"In at least one case, we are able to see chronic cortical thickening with no marrow or soft tissue signal abnormality, indicating callus from an old or healed rib fracture. This would be completely missed on conventional MR imaging," he adds.

Changing patient management

The use of oZTEo has changed patient management and, ultimately, the clinical outcome in several cases at Shields Health Care Group (Figures 1-4).

Figure 1. A 20-year-old professional hockey player with left sided pain at L5 when skating. (B, 1) Initial diagnosis without oZTEo was edema in pedicle and transverse process on STIR, sclerosis in pars on T1 and no fracture identified. With oZTEo, (C, 2) an unsuspected partial fracture of left L5 pars was detected. (D, 3) One month follow-up MR shows a slight increase in the extent of the fracture, requiring increased time away from the sport. This case highlights the value of oZTEo in patient management. (A) Sagittal T1 FSE, (B) sagittal STIR FSE, fracture not visible (yellow circle), (C) oZTEo demonstrating incomplete fracture of the pedicle and (D) oZTEo at one month follow-up showing slight enlargement of the fracture requiring further rest.

Figure 2. A 12-year-old high-level gymnast with back pain on extension. (A, B) First MR without oZTEo showed mild spondylolisthesis with no pars defect. (C, D) Follow-up MR five months later with oZTEo shows (1) chronic pars fracture on left side and (2) sclerosis on right side. Also important, this adolescent patient did not need CT for diagnosis and management, reducing radiation dose. If the oZTEo technology would have been available for the first MR exam, the pars fracture may have been detected and the patient could have rested and not have the fracture turn into a chronic issue. (A) Sagittal T1 FSE, (B) sagittal T2 FSE, (C) sagittal oZTEo (acquired) and (D) axial oZTEo (reformat).

Figure 3. A 14-year-old high-level gymnast with back pain. (C, 1) In the MR exam without oZTEo, continuous marrow signal without edema on the left side is consistent with no pars defect; right sided pars defect was identified. (D, 2) In the MR exam with oZTEo, a bilateral L5 pars defect (left side only seen on oZTEo) with likely partial healing on the left. oZTEo helped determine that partial healing on the left side needs protection and athlete needs prolonged rest from sport. (A) Sagittal T1 FSE, (B) 3D sagittal T2, (C) 3D axial T2, (D) sagittal oZTEo (acquired) and (E) axial oZTEo (reformat).

In each of the cases presented, none of the patients required or received CT or SPECT/CT imaging due, in part, that it was deemed unnecessary after conclusively visualizing the pars defects using oZTEo. It’s important to note that there are actually three benefits of oZTEo. Dr. Pechet explains that for the patient, they save time because no additional appointment or imaging study is necessary; they are exposed to less radiation exposure because CT and follow-up radiographs are unnecessary; and they may have lower costs or no co-pay for an additional exam.

"We have received early acceptance for imaging of the spine for extension-based back pain, especially in gymnasts, where spondylolysis is a common finding. I anticipate that oZTEo will gain acceptance in the assessment of the hip for FAI and the SI joint, both areas where pelvic radiation exposure in adolescents is an issue with CT."
Imaging of the shoulder, wrist and foot are areas where Dr. Pechet would like to further explore with oZTEo. He explains that imaging of the cervical neural foramina is challenging with MR as GRE-based sequences tend to overestimate the degree of foraminal narrowing and T2 sequences can suffer from poor foraminal fat signal, especially at 3.0T.
"Shoulder surgeons often use surface renderings of CT images of the shoulder for planning purposes, and I believe that oZTEo may likely be used in the same way," he says.

Figure 4. A 15-year-old athlete with a history of 8/10 low back pain. (A and D, 1) Conventional MR including 3D T2 show marrow edema in both L3 pedicles without fracture, classified as Hollenberg grade 1. (C and F, 2) oZTEo five days later shows bilateral near complete L3 pars fracture, classified as Hollenberg grade 2/3, requiring extended period away from sport to allow healing. Because of oZTEo, this adolescent patient did not need CT to diagnose, reducing radiation dose. Follow-up study to track progression with oZTEo (instead of CT) again reduced radiation exposure. Patient left side: (A) Sagittal STIR FSE, (B) 3D sagittal T2, and (C) oZTEo. Patient right side: (D) Sagittal STIR FSE, (E) 3D sagittal T2 and (F) oZTEo.