Current events in cardiopulmonary radiology, updates about the journal’s web site features, and links to other web sites of interest to cardiopulmonary radiologists.
Thursday, July 10, 2014
Part III. Elements of good scan protocols: Building blocks of a good practice
There is no dearth of good scanning protocols on the web and in the journals, and yet one of my favorite place for a great protocol template lies in the public domain at the American Association of Physicists in Medicine website (http://www.aapm.org/pubs/CTProtocols/documents/AdultRoutineChestCT.pdf). The outstanding Working Group on Standardization of CT Nomenclature and Protocols has comprehensively described the nuances of a few common protocols for all major CT vendors. Even if one might not completely agree with the actual scan parameters, I find it hard to argue against the exquisitely structured protocols, which start at the level of clinical indication and then address patient positioning, contrast injection details, breathing instructions, and scan range. If you are in the business of making CT protocols, the site is a must visit!
In a good CT protocol, the header should state body region, protocol title, scanner details (name, vendor, slice profile) and version date. I am fond of stating to our technologists “With some luck I can fix noise and some artifacts, but I have no chance against chest CT compromised by motion artifacts.” This brings me to the amazing why, what, and how manual on respiratory instructions for CT of the lungs by Bankier and colleagues (1). For a chest CT, the best conversation a CT technologist can have with the patient pertains to breathing during scanning. No scan parameter is as important as clear, concise, correct breathing instructions for chest CT.
Once these crucial elements of scanning are addressed, you can then begin to populate specific scan parameters for planning radiographs (scout images), which serve several purposes beyond just planning the scan range. Parameters for transverse CT images should include specific values for scanning mode, kV, mA (or automatic exposure control descriptors), rotation time, detector configuration, table feed per rotation, pitch, reconstruction approach (filtered back projection or iterative reconstruction), reconstruction filter, field of view kernel or algorithm, section thickness, as well as section interval. Specifications for additional thin sections, coronal and sagittal multiplanar reformats and maximum intensity projection images should be clearly stated. We will discuss each of these items in separate blogs, I promise.
I personally prefer Excel, Spreadsheet or Worksheets to create and archive our protocols. Separate files are created for individual clinical indication based protocols. Each spreadsheet can have different pages or tabs for different CT scanners. I never use identical scan protocols for identical clinical indications for different CT scanner types. This ensures that one capitalizes upon individual strengths of different scanners.
1. BankierAA, O’Donnell CR, Boiselle PM. Respiratory instructions for CT examinations of the lungs: a hands-on guide. RadioGraphics 2008; 28: 919–931
Tuesday, June 24, 2014
The July 2014 issue of JTI has been published in print and on-line.
This issue includes a review article by Y. J. Cho and colleagues entitled “Iterative Image Reconstruction Techniques: Cardiothoracic Computed Tomography Applications.” The authors of this article review the types of iterative reconstruction, discuss applications in cardiothoracic CT, and address radiation exposure issues.
A number of original research articles are also included in this issue of JTI. One of the original research articles is a systematic review performed by A. Raymakers and colleagues, evaluating cost-effectiveness analyses for CT pulmonary angiography for pulmonary embolism.
Dr. J Ackman and colleagues report on their survey of members of the Society of Thoracic Radiology regarding the current state of nonvascular thoracic MRI. Their results show that nonvascular thoracic MRI is still in its early phase, with surveyed cardiothoracic radiologists reporting overall limited experience with and unclear recognition of value of nonvascular thoracic MRI yet an eagerness to increase knowledge and utilization.
Web-only content in this issue includes the ACR Appropriateness Criteria® for nonischemic myocardial disease with clinical manifestations (ischemic cardiomyopathy already excluded).
The next installment of the popular Signs in Cardiopulmonary Imaging feature is the “Incomplete Border Sign” by C. Hsu and colleagues.
Finally, Society of Thoracic Radiology (STR)
announcements include the 2014 Gold Medal Award of the STR winner, Dr. Sanford Rubin; the 2014 STR Inspiration Award given to Dr. Ella Kazerooni, and published abstracts from the 2014 Society of Thoracic Radiology annual meeting and postgraduate course.
Wednesday, June 18, 2014
Published ahead-of-print in JTI is the next installment of Expert Opinion, addressing the U.S. Preventive Services Task Force (USPSTF) recommendation on screening for lung cancer. The USPSTF issued a grade B recommendation for low-dose CT screening for lung cancer in December 2013 for smokers age 55-80 years old with at least a 30 pack-year smoking history or former smokers in the same age range who quit within 15 years. Under the Affordable Care Act, private insurers will be required to cover screening for these patients beginning in 2015.
The JTI editorial staff asked this group of experts, “if you were given the opportunity to make one modification to the recent lung cancer screening recommendations from the [USPSTF], what would it be and why?” To find out what our experts had to say, you can find the article here
Sunday, June 08, 2014
II: Personalizing Chest CT Protocols
It is not my intent to enter into the minefield of risks of low radiation doses such as those associated with CT scanning. Yet I must re-affirm my belief that prudent use of radiation dose in CT scanning must not be an optional aspect of any CT practice. On the other hand, while quest to bring CT doses for certain thoracic indications closer to a few chest radiographs has already begun, until that point of “miniscule” dose is reached or crossed, a certain caution is important to protect the diagnostic information from this precious imaging modality. This aspect of prudent radiation dose utilization brings us to an important matter of personalizing CT protocols depending on clinical requirement or need. Stratification of CT protocols can and does help in ensuring “just-enough” doses from CT. I like to qualify the ALARA as radiation dose as low as reasonably achievable for specific clinical indication.
Before the scanner description and scanning parameters populate a CT protocol, comes the clinical indication or reason for scanning. No other scanning attribute is as important as a justifiable clinical indication for CT scanning. The best clinical justification for CT scanning results in the best benefit to risk ratio for CT. Based on the similar clinical indications, we should stratify the chest CT protocols so as to enable maximum efficiency and least errors in selection of appropriate CT radiation doses.
Several different clinical indication-based CT protocols can be applied to chest imaging so that we do not use a “one size fits all” approach. The thoracic imaging division should at least have a few specific CT protocols such as routine chest, CT pulmonary angiography, lung nodule follow up CT, lung cancer screening CT, diffuse lung disease CT (also called high resolution CT of the chest), tracheal protocol CT, and chest wall protocol. Such stratification of protocols can help optimize radiation dose according to clinical requirements.
For example, radiation dose for both lung nodule follow up CT and lung cancer screening CT should be lower than the routine chest CT protocol. Creation and review of maximum intensity projection (MIP) images helps improves detection of lung nodules while averaging out image noise in low dose images. Likewise, a distinct CT pulmonary angiography protocol must utilize weight based or software based lower tube potential (kilovoltage) as well as limited scan coverage up to lung bases only as compared to routine chest CT protocol. Thinner sections help reduce partial volume artifacts and improve sensitivity for detection of pulmonary embolism.
CT for diffuse lung disease is another distinct protocol that should spell out policies for acquiring expiration phase images either as a step-and-shoot (non-helical or axial) acquisition of representative sections with gaps or as a low-dose volumetric (helical) acquisition from lung apices to bases. To maximize spatial resolution, a diffuse lung disease protocol should also involve reconstructing thin sections with higher spatial frequency kernels (aka sharper algorithm, kernel or filter) at smaller reconstructed field of view from rib-to-rib coverage. Prone images likewise may not be necessary in all patients.
Evaluation of the trachea with CT, though not as frequent as some of the other indications, nonetheless warrants an additional protocol to ensure optimum scan coverage (from base of the neck to the lung bases in inspiration and up to the bifurcation in dynamic expiration). The importance of appropriate breathing instructions and compliance cannot be over-emphasized for chest CT, particularly for diffuse lung disease and tracheal protocol CT examinations.
Once CT protocols are stratified according to clinical indications, we should then sub-stratify these individual protocols according to the scanner types (number of sections (4-, 8-, 16-, or 64-row multidetector row CT) and vendors. Different CT systems have unique capabilities and therefore unique requirements for scanning parameters. Thus, for example, lung nodule follow up protocols should be created for different CT systems (separate protocols for Siemens 64-section versus Toshiba 64-section). This may sound onerous and forbidding but in reality is not an insurmountable task.
In the next blog, I will discuss the elements of good scan protocols, including the need to follow some uniform protocol codes that can simplify our lives in terms of protocol and dose comparisons.
Email me at MKALRA@mgh.harvard.edu
with your comments and questions.