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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_6032_Библиотеки_им_академика_М_И_Перельмана
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Figure 8
Bone scintigraphic scan shows diffuse metastatic “hot”
lesions in the spine, femur, ribs, and other bones. Activity is
minimal in the kidneys and bladder as a result of “super scan” when
activity is abundant and increased throughout the skeletal system.
A three-phase bone scan is available to examine for blood flow, blood
pool, and delayed images for infection. However, in spine imaging, MRI with
contrast is more frequently the imaging modality of choice to detect infection.
The predominant use of 99Tc MDP bone scanning is to image areas of
fractures or metastatic bone lesions in the spine.
The amount of radiation from bone scanning is low compared with that
from CT. Although the isotope adheres to the bone, it is excreted through the
kidneys. Therefore, the largest pool of radioactive activity is in the bladder
and urine, lasting approximately 24 hours. Patients should be instructed in
proper voiding and hand hygiene after the procedure by the nuclear medicine
personnel.
PET is used for the detection of metastatic disease in the spine and soft
tissues of the body. Although the literature reports conflicting sensitivities for
PET compared with bone scanning, many medical practices use PET because
it can help identify both bone and soft-tissue tumors.
15
The 18F fluorodeoxyglucose (FDG) produced from a cyclotron is
administered via venous injection. After a short period, CT images are
obtained followed by multiple sections of the body obtained with PET. Both
PET and CT are performed with the same scanner, with registration of both
sets of images.
The isotope 18F FDG shows increased activity in tissues with elevated
glycolytic activity. Ceroplastic cells have increased glycolysis; therefore, the
cells show abnormally elevated activity with PET. False-positive FDG uptake
can occur in infection, inflammation, and sarcoidosis (Figure 9).
MRI of the spine is often performed to complement PET findings for
defining tumor involvement. Although PET/CT has a CT component, the
images are of lesser quality and used mostly for localization purposes.
Additional high-quality CT often is needed for surgical planning.
Administrative logistics are involved in obtaining reimbursement for PET
scans from the Centers for Medicare and Medicaid Services. A requirement is
data entry into the National Oncologic PET Registry,16 with a limited number
of allowable PET scans for the patient incident creating some delay for
emergent PET scans for patients with Medicare as the primary insurance.
Intraoperative Fluoroscopy
Fluoroscopy is frequently used in the operating suite to localize the surgical
level and to guide the placement of radiopaque implants. Understanding the
basic radiation exposure precautions is important for both the patient and the
equipment user and surgical team when performing image-guided spine
procedures.
The ACR presented a white paper on radiation doses in medicine.17 Highdose radiation has increased the risk of stochastic effects of carcinogenesis.
However, the more immediate concern is the deterministic effect of radiation
dose to the body surface, including erythema, skin damage, hair loss,
cataracts, and radiation sickness. Therefore, the FDA mandates the display of
cumulative radiation delivered from new fluoroscopic equipment, which
requires close monitoring by the equipment user and the technologist.
18
Figure 9
Positron emission tomographic scan shows tumor activity
not only in the vertebral body (long arrow) but at the lymph
nodes (short arrow).
It is essential that the user of the fluoroscopic unit in the operating suite
understand the basic risks and the use of the equipment, including the
measurement units of Grays for radiation dose and sieverts for the equivalent
dose based on the type of radiation (x-ray, α, β radiation, and so forth).
The equipment user and the team should follow a few guidelines when
using intraoperative fluoroscopy. For the equipment user, the main concern
relates to scatter radiation. Because radiation decreases with distance, the
equipment user should stay away from the patient as much as possible when
using C-arm fluoroscopy. A lead apron is mandatory when close to the
intraoperative C-arm for all personnel. Wearing a thyroid shield is strongly
recommended because the shield substantially decreases radiation to the
thyroid gland. Protective goggles are recommended as often as possible.
Avoiding placement of the equipment user’s hands in direct exposure of the
radiation beam is important. If possible, collimation (narrowing aperture at
the source) should be used to deliver radiation only to the essential part of the
imaging target to minimize overall radiation exposure.
19
Intraoperative CT
Intraoperative CT is being used more often because of its increased accuracy
in the placement of spine hardware. The surgeon and other personnel should
be outside the operating room or behind sufficient lead shielding during
intraoperative CT to minimize scatter radiation. The two settings selected are
peak kilovoltage and milliamperes. Most CT scanning programs automate the
peak kilovoltage and milliampere variables to produce best-quality images,
often at a high radiation dose. Manual minimization of the two variables will
result in poor image quality, but at a low radiation dose to the patient.
Increasing the two variables will produce better image quality, but at a high
radiation dose to the patient. Larger body size also requires a higher radiation
dose to visualize the spine structures. Therefore, close interaction with the
technologist in determining the optimal setting becomes an important
component to understand when using intraoperative CT. Otherwise, the
Figure 10
radiation delivered to the patient will increase. In addition, decreasing the
total number of scans decreases overall radiation to the patient, which is
preferred.
After the images are acquired, the data can be formatted to accentuate the
tissue of interest. Another component of the CT image focuses on software
processing of the acquired data, described as a CT algorithm. After obtaining
the CT scan, the data can be formatted into different algorithms. If soft tissue
is of interest, a lower kernel algorithm (approximately 30 HU) is used. For
bone or hardware, a higher kernel algorithm (approximately 60 HU) creates
sharp bone margins. Repeat scanning is not necessary to obtain images with
these different algorithms because the technologist can reformat the data into
the preferred algorithm. After the data are formatted, the window setting
(Hounsfield levels) can be changed so that the tissue of interest can be seen.
This concept is best understood as a 2 × 2 matrix (Figure 10). When
examining soft tissue, a lower kernel algorithm and soft-tissue window is
optimal. When looking for a bone fracture, a higher kernel algorithm with
bone window is preferred. A soft-tissue algorithm with bone window will
still show bone margins of acceptable quality, but with less sharpness. A
bone algorithm with soft-tissue window often is not of nondiagnostic use.
Axial CT scans of the spine show a bone algorithm and
bone window (A), a bone algorithm and soft-tissue window
(B), a soft-tissue algorithm and bone window (C), and a soft-tissue
algorithm and soft-tissue window (D).
A recent meta-analysis compared a less invasive surgical approach with
open spine surgery and showed an increase in radiation exposure to the
surgeon and the team.20 Many variables affect the magnitude of increase in
the delivered radiation and scattered radiation. Many imaging specialists
think that the amount of radiation increase may not be significant, although
the overall effect of the increase in radiation is not known. Therefore, it
becomes prudent to decrease radiation whenever possible by understanding
the basics of radiation delivery and by determining ways to minimize
radiation to the equipment user and the patient. Concepts in radiation-based
image guidance are an important educational component in the use of imageguided intraoperative procedures.
Summary
Imaging of the spine entails understanding of the various imaging modalities
available that will provide the best imaging information for subsequent
patient treatment. The provider or the referring clinical team also must
understand the limitations of imaging and the risks associated with the
delivery of energy for image acquisition. Also, understanding the available
national guidelines for the appropriate use of imaging is important for the
safety of the patient and the quality of clinical treatment.
Key Study Points
Understanding the basic concepts of radiation dose is important in
requesting imaging studies and in the use of intraoperative imaging
equipment.
Myelography, MRI, and PET have detailed assessments performed before
and after imaging that are required for patient safety.
Guidelines and appropriate use for imaging of the spine continue to be
developed among multiple national societies and should be referenced
whenever possible to plan directed, value-based treatment.
Annotated References
1. American College of Radiology: ACR Appropriateness Criteria. Update 2016.
Available at: http://www.acr.org/Quality-Safety/Appropriateness-Criteria. Accessed
January 30, 2017.
The ACR AUC are evidence-based guidelines designed to assist referring clinicians in
ordering the most appropriate study based on clinical presentation. Expert panels
including radiologists and other specialists developed the guidelines.
2. North American Spine Society: Evidence-based clinical guidelines for multidisciplinary
spine care: Diagnosis and treatment of degenerative lumbar spondylolisthesis. Revised
2014. Available at:
https://www.spine.org/Portals/0/Documents/ResearchClinicalCare/Guidelines/Spondylolisthesis.pdf
Accessed January 30, 2017.
Evidence-based guidelines for the treatment of lumbar spondylolisthesis and
recommendation grades based on high-level evidence are presented.
3. North American Spine Society: Evidence-based clinical guidelines for multidisciplinary
spine care: Diagnosis and treatment of adult isthmic spondylolisthesis. 2014. Available
at:
https://www.spine.org/Portals/0/Documents/ResearchClinicalCare/Guidelines/AdultIsthmicSpondylolisthesis.pdf
Accessed January 30, 2017.
Evidence-based guidelines for the treatment of lumbar isthmic spondylolisthesis and
recommendation grades based on high-level evidence are presented.
4. American College of Radiology: Manual on contrast media v10.2. 2016. Available at:
http://www.acr.org/quality-safety/resources/contrast-manual. Accessed January 30,
2017.
This manual produced by the ACR Committee on Drugs and Contrast Media presents
up-to-date information and an evidence-based discussion of the use of contrast media in
radiology, with a focus on enhancing safe and effective use.
5. Davenport MS, Cohan RH, Khalatbari S, Ellis JH: The challenges in assessing contrastinduced nephropathy: Where are we now? AJR Am J Roentgenol 2014;202(4):784-789.
The authors review the history of contrast-induced nephropathy and discuss difficulties
in establishing a causative relationship between currently used low-osmolar contrast
media and contrast-induced nephropathy in the clinical setting. They suggest that
contrast-induced nephropathy is real, but it is rare. Level of evidence: IV.
6. Davenport MS, Khalatbari S, Cohan RH, Dillman JR, Myles JD, Ellis JH: Contrast
material-induced nephrotoxicity and intravenous low-osmolality iodinated contrast
material: Risk stratification by using estimated glomerular filtration rate. Radiology
2013;268(3):719-728.
The authors report on a retrospective study of 20,242 patients who underwent CT either
without or with intravenous contrast. It was concluded that intravenous low-osmolar
iodinated contrast is a risk factor for acute kidney injury, but not in patients with a
stable serum creatinine level less than 1.5 mg/dL. Level of evidence: III.
7. Lin EC: Radiation risk from medical imaging. Mayo Clin Proc 2010;85(12):1142-1146,
quiz 1146.
8. Nazarian S, Beinart R, Halperin HR: Magnetic resonance imaging and implantable
devices. Circ Arrhythm Electrophysiol 2013;6(2):419-428.
The authors discuss MRI in patients with implanted defibrillators, focusing on physics,
nonclinical testing, prior clinical studies, safety protocols, and MRI quality.
9. Fedutes BA, Ansani NT: Seizure potential of concomitant medications and radiographic
contrast media agents. Ann Pharmacother 2003;37(10):1506-1510.
Probl Diagn Radiol 2011;40(4):149-157.
The authors discuss the use of myelography in patients with spinal pathology and neck
or back pain, including indications, patient workup and planning, procedure technique,
and postmyelographic care. Level of evidence: IV.
artifacts in MRI. AJR Am J Roentgenol 2011;197(3):547-555.
This article reviews the source of imaging artifacts arising from metallic hardware and
includes a discussion on how to reduce artifacts by adjusting imaging parameters to
produce more clinically useful images. Level of evidence: IV.
devices: Explanation of terminology. Radiology 2009;253(1):26-30.
2012;199(1):W17-W23.
A detailed discussion of nephrogenic systemic fibrosis, including history, possible
pathophysiology, and presentation/diagnosis, is presented. The authors provide
recommendations for safe use of gadolinium-based contrast agents in the setting of
known or possible renal dysfunction. Level of evidence: IV.
spine care: Diagnosis and treatment of degenerative lumbar spinal stenosis. Revised
2011. Available at:
https://www.spine.org/Portals/0/Documents/ResearchClinicalCare/Guidelines/LumbarStenosis.pdf
Accessed on January 30, 2017.
Evidence-based guidelines for lumbar spinal stenosis and recommendation grades based
on high-level evidence are presented.
bone metastases. Semin Nucl Med 2005;35(2):135-142.
https://www.cancerpetregistry.org/clinicians.htm. Accessed March 13, 2017.
The purpose of this registry is to safeguard access to Medicare reimbursement for
certain types of PET scans.
College of Radiology white paper on radiation dose in medicine. J Am Coll Radiol
2007;4(5):272-284.
Revised April 1, 2016. Available at:
http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?FR=1020.32.
Accessed January 30, 2017.
This FDA report provides guidelines for monitoring the performance of ionizing
radiation–emitting products.
orthopaedics: A review of the ALARA (As low as reasonably achievable) principle.
Patient Saf Surg 2016;10:27.
This review article discusses the basics of fluoroscopy and methods to decrease the dose
of radiation to the patient, operator, and other staff in an orthopaedic operating room.
exposure? A systematic review. Clin Orthop Relat Res 2014;472(6):1738-1748.
This systemic review of radiation exposure in spine surgery was performed to
determine the difference in radiation exposure in open versus less invasive spine
procedures, radiation exposure based on the position of the surgeon, and radiation
exposure using C-arm fluoroscopy compared with fluoroscopy with computer-assisted
navigation.
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