Ask the Expert: ACR CT Scanner Accreditation

Welcome to Computed Tomography American College of Radiology Accreditation.  Total estimated time to complete this course: 30 minutes                                                This e-learning covers the following topics:   1. Revisions made to the ACR CT accreditation process 2. The clinical requirements of ACR CT accreditation 3. The new ACR phantom testing requirements 4. The common problems and pitfalls that occur during the submission process CT Accreditation Program now provides: Modular accreditation structure New submission process New scanner testing procedures This training provides up-to-date information on:  changes requirements procedures Appropriate, timely training for those who are: in the planning stages involved in the CT Accreditation process anticipating a future accreditation renewal Department managers Radiologists Lead CT technologists Medical physicists New testing process for the ACR phantom New CT thresholds New quality assurance/quality control program requirements New ONLINE application process New phantom testing guidelines Scan the ENTIRE phantom from beginning to end Scan the phantom exactly as your ROUTINE scanning protocol is listed on your phantom data form (the OLD Table 1) with a few exceptions: Do NOT use CARE Dose, CARE Dose4D™, or any type of dose modulation when scanning the phantom Use an appropriate DFOV for the phantom size (Recommendation: 220mm displays full phantom and image text) Do not submit additional recons such as bone or lung window Do not submit thin recons that would be used for 3D multi-planar reformations (MPRs) Do not submit any sagittal, coronal, or oblique MPRs ACR: only scan and submit the initial axial reconstruction that would be used for primary interpretation Changes to reference and pass/fail criteria for the CTDIvol (mGy) for dose Adjustment to the polyethylene CT number accuracy range Examination Pass/Fail Criteria Reference Levels  CTDIvol (mGY) CTDIvol (mGY) Adult Head 80 75 Adult Abdomen 30 25 Pediatric Head (1 year old) 40 35 Pediatric Abdomen (5 years old, 40-50 lbs.) 20 15 New guidelines: significant change to CT number accuracy range for polyethylene Previous guidelines: Polyethylene =  -107 to -87 HU   NEW guidelines: Polyethylene =  -107 to -84 HU   For more information, see the ACR website's accreditation page. Range settings 1. A continuous quality control (QC) program must be established for all CT units with the assistance of a qualified medical physicist. 2. The qualified medical physicist should determine the frequency of each test and who should perform it based on the facility and CT usage. 3. Policies and procedures related to quality, patient education, infection control, and safety should be developed and implemented as part of a quality assurance program. The ACR no longer sends the bulky application packet and instructions via regular mail. Once registered for accreditation, all forms required to fill out are to be submitted online via the ACR’s website. The only information you will receive via the mail are the barcode stickers for putting on your films or CD/DVDs and a memo. Exams submitted for clinical evaluation must come from the list given in the CT accreditation program requirements. At least one chosen examination per unit must be specialized (*). Units applying for cardiac must submit at least one CTA examination. Exception: pediatric-only units (patients 0 to 15) must submit the pediatric cardiac examination for the cardiac module. If the CT system scans BOTH adult and pediatric patients, at least one exam must also be from a child (ages 0 to 15). ACR’s new cardiac module has very specific guidelines. If you scan any type of cardiac examination, you must submit a cardiac case. Head/Neck Chest Abdomen Cardiac Head Chest Abdomen Calcium Score Temporal Bones* PE* Cirrhosis* CTA* Cervical Spine HRCT of Chest* Known Renal Mass* Pulmonary Vein Mapping   Aortic Dissection*   Pancreatic Carcinoma*   Cardiac Function & Morphology * Specialty exam Head/Neck Chest Abdomen Cardiac Pediatric Head Pediatric Chest Pediatric  Abdomen Pediatric   Cardiac Pediatric Sinus Pediatric HRCT   of Chest* Pediatric CT for  adrenal/renal    mass* Pediatric Cervical Spine* Pediatric Temporal  Bones* * Specialty exam ACR phantom description Phantom module tests for accreditation CT number accuracy Low contrast CT number uniformity Artifacts Dosimetry phantom testing – CTDIvol Pass/fail criteria REQUIRED: Use a specific Gammex 464 ACR phantom for ALL CT scanners Only acceptable phantom for CT ACR testing Phantom order form on ACR website No requirement to purchase phantom May borrow phantom NOTE: There is no substitute phantom for the Gammex 464 ACR CT Phantom The ACR CT phantom is made as a solid one-piece construction using water-equivalent material. ACR phantom with the external laser lights aligned to the white scribe markings on the axial, coronal, and sagittal axis The five cylinders of testing materials:   Water Polyethylene Teflon / "Bone" Air Acrylic Polyethylene Module 1 (CT number accuracy and slice thickness)   Used for initial ACR phantom positioning & alignment; consists of: Four 1 mm BBs (outer edge positions: 12, 3, 6, & 9 o’clock) Five cylinders of material: “bone,” polyethylene, water equivalent material, acrylic, & air Two ramps of wires to determine image thickness Module 2 (Low contrast resolution-CNR)   Used to measure low contrast resolution; consists of: One 25 mm cylinder & four sets of four cylinders (diameters: 2 mm, 3 mm, 4 mm, 5 mm, & 6 mm) 25 mm cylinder used to determine the contrast to noise ratio in comparison to the background material Module 3 (CT number uniformity)   Uses “tissue-equivalent” material to assess CT number uniformity Two BBs to measure in-plane distant measurement accuracy Module 4 (High contrast resolution) Evaluates high contrast or spatial resolution; consists of: Eight bar patterns for determining the smallest visible line pairs: 4, 5, 6, 7, 8, 9, 10, & 12 Lp/cm Set-up, align, and scan the phantom for the following tests: CT number accuracy Low contrast resolution   CT number uniformity Artifacts Use ACR phantom to comply with required QA/QC program Image thickness High contrast resolution Image noise Distance measurement Pull back table padding Use the white external lines of the phantom in all planes to align the Gammex 464 CT accreditation phantom on the table axial (z-axis, cranial/caudal) coronal (y-axis, anterior/posterior sagittal (x-axis, left/right)  Choose Head First – Supine patient position Once visually aligned, center internal lasers on white scribe line at center of Module 1 (FOOT END of the phantom) and ZERO the table at this point To begin scanning the phantom, center on white scribe line of Module 1 at the FOOT end of the phantom   1. Take the alignment scan for verification of alignment 2. Select ThoraxHRSeq protocol to perform the alignment scan 3. Routine tab: Set the number of scans to “1” and the slice width to ≤ 2 mm 4. Uncheck the CARE Dose4D box 5. Scan tab: Change the feed to zero 6. Recon tab: A. Change the FOV to 220 B. Change the kernel to B31 C. Change the windowing to abdomen 7. Take a sequential at the S0 position 8. Evaluate image for alignment Routine tab: check slice width, number of scans & images, table position, begin & end Scan tab: turn OFF CARE Dose4D. Verify slice width is ≤ 2 mm.   Recon tab: option to rename series description; change the FOV to 220 mm; the kernel to B31; and the window to abdomen   Outcome WW = 1000 and WL = 0 All four BBs are visible Longer central wires are symmetrical The phantom is scanned with certain exam protocols based on the site’s application and what modules they scan.  The ACR will let the site know the specific modules that must be scanned with the phantom. ALL sites will scan the phantom with an adult abdomen protocol, even if they only scan pediatric patients. CT number accuracy test for all five substances is measured using the adult abdomen protocol only. Append the next module you wish to scan to your alignment scan, adjust the table begin/end to S0-S120, adjust your scan direction if needed. Be sure the slice width, kV, and mAs match your phantom data form.   Change the FOV to 220 mm and be sure begin and end are correct. Check the kernel and window to be sure they match the phantom data form for this module routine protocol.   Use the adult abdomen protocol to evaluate all five materials. Measure only the water CT number for all of the other protocols you are submitting for the phantom portion of your accreditation submission. Select the best image from module 1 of the ACR phantom. Image must show the longest wire +/- 1 wire from the center of at least one of the top and bottom ramps.   Material CT # Range Water -5 to +5 HU Air -970 to -1005 HU Teflon (Bone) 850 to 970 HU Polyethylene -107 to -84 HU Acrylic 110 to 135 HU Adult abdomen protocol only for ALL five materials Best image from Module 1 of the ACR phantom WW = 400 and WL = 0 ROI must be proper size and placement: ≈200mm2 Low contrast resolution test is now calculated as a contrast-to-noise ratio or CNR CNR for adult head, pediatric head, and adult abdomen protocols must be greater than 1.0 CNR for the pediatric abdomen protocol must be greater than 0.5 Formula: CNR = |A-B|/SD A is the mean of the ROI inside the 25 mm rod B is the mean of the ROI outside the 25 mm rod SD is the standard deviation of the ROI outside the 25 mm rod Do NOT take into consideration if the CNR is a negative or positive number Perform on all submitted protocols Best image from module 2 of the ACR phantom WW = 100; WL = 100 ROI must be proper size and placement: ≈ 100mm2 CNR = |A-B|/SD Review using the adult abdomen protocol images Best image from module 3 of the ACR phantom WW = 100; WL = 0 ROI must be proper size & placement: ≈ 400mm2 Use the same image adult abdomen protocol, which you used for the CT uniformity test. Turn off all graphics and dim the lights. Review the image carefully for any type of artifacts such as streaks or rings. You must record the presence of any artifacts. If artifacts are present, notify your physicist and possibly your service engineer for further investigation. Strategies to avoid issues that arise during the accreditation and submission process: Read through all of the guidelines and instructions long before starting the actual scanning Read, understand, and follow the ACR’s specific accreditation process instructions Ask either the ACR or Siemens for clarification before continuing the process Enter correct information into phantom data forms and CTDI dose spreadsheet Be Prepared! Nomenclature in ACR guidelines: based on different vendors’ systems Terms may be unfamiliar to you The next charts: Clarify the different nomenclatures Break down major terms Show location of examination platform information ACR Siemens Found? mA Eff mAs Routine/Scan Tabs Time per Rotation(s) Spiral=Rotation Time Sequence=Scan Time Scan Tab SFOV Scan Field of View Not displayed DFOV FOV Recon Tab ACR Siemens Found? # data channels (N) Data channels Routine/Scan Tabs A: Table Increment Feed (Seq. scans only) Scan Tab H: Table Speed Feed per Rotation (Spiral scans only) N x T x Pitch Pitch Pitch (Spiral scans only) Scan Tab Parameter Formula Example mA (eff mAs ÷ rotation time)  x  pitch (160 eff mAs ÷ 0.5s) x 0.8p = 256 mA Effective mAs (mA x rotation time) ÷ pitch (256 mA x 0.5s) ÷ 0.8p = 160 eff mAs Pitch feed per rotation ÷ (# detector rows x collimated slice width) 19.2 mm ÷ (16 x 1.2) = 19.2 ÷ 19.2 =  1.0 pitch The Definition® FLASH and Definition® Dual Source detector configurations     Definition FLASH Definition Dual Source (DS) Definition AS+ 128 Definition AS 40 Definition AS 64 Definition AS 20 Sensation® 64  Sensation® 40  Sensation® OPEN Sensation® 16 Sensation 10 Volume Zoom / Sensation 4 Emotion® 16 Emotion® 6 Emotion® Duo Tube current (mAs) The product of the x-ray tube current (mA) and the exposure time (s). mAs determines the amount of photon or quantum delivered in the x-ray beam. It affects the patient dose and image noise.  In sequence scans, the mAs indicates the applied dose. In spiral scans, the applied dose is also affected by the pitch factor. Effective mAs (Also eff. mAs) Introduced with SOMATOM® multi-slice scanners. Eff. mAs takes into account the influence of pitch on both the image quality and dose.  Effective mAs = mAs ÷ pitch factor. This principle is employed in the SureView concept. mAs per rotation (mAs/rot) For cardiac scanning. Determines a value per rotation that is independent of the pitch factor. SureView A Siemens proprietary multi-slice CT concept that permits easy scan parameters selection for routine spiral scanning. The SureView concept offers the following advantages: Constant image quality (noise and slice width) REGARDLESS of the   pitch value. Tube current (mA) is automatically adjusted to maintain the same dose independent of pitch. Freely selectable pitch that can be tailored to the patient and study requirements. Rotation Time The time required for one complete 360° rotation of the tube-detector system. It determines the speed and temporal resolution of the acquisition. Collimation (total collimation or z-coverage) Determines the slice or section thickness that will be utilized for a particular CT scanning procedure. Selecting the collimation determines the tube collimation by narrowing or widening the x-ray beam. Slice collimation Affects the quality of the acquisition data. It determines the minimum slice width that can be used for image reconstruction. The slice collimation in a multi-slice CT is related to the size of the detector elements and the detector configuration. Slice width The thickness of the reconstructed image and should not be confused with the collimation in multi-slice CT systems.  Using the Siemens proprietary SureView concept, the reconstructed slice width is independent of the pitch for any Siemens multi-slice CT scanners. Feed The distance the table travels during sequential scanning. When the feed exceeds the slice collimation or total collimation, there are gaps in the acquisition. When the feed is less than the slice collimation or total collimation, overlapping raw data is acquired. Feed per rotation (feed/rot) The distance the table travels during one gantry rotation during spiral scanning. Pitch (pitch factor) A spiral scanning parameter determining the patient table speed and the speed of acquisition. The higher the pitch value, the faster the table travels and the shorter the scan duration. Kernel (algorithm or filter): Image sharpness: defined by the numeric value Letter after number = scan mode s refers to standard mode f for fast mode h for high resolution modes a reconstruction parameter affecting image sharpness and noise Higher number = sharper and noisier image Examples B30f: a body fast mode medium smooth kernel H70s: a head standard mode sharp kernel The different types of kernels are:     H stands for Head                                B stands for Body   U stands for Ultra High Resolution         C stands for Child Head   S stands for Special Applications           D stands for Dual Energy   Field of View (FoV): determines the area of anatomy displayed within the CT image, the display FoV (DFOV) To improve spatial resolution significantly: Use a smaller FoV because it reduces pixel size FoV is limited by the maximum size of the scan measurement fields, scan FoV (SFOV). For body imaging: Maximum SFOV of 50 cm Maximum SFOV for head imaging and the ultra-high resolution scan modes (UHR): 30 cm   ACR Siemens Found? Reconstruction Algorithm Kernel Recon Tab Axial (A) Sequence (Seq) Routine Tab Helical (H) Spiral (Spi) Routine Tab Z-axis collimation (T) Collimator size Routine/Scan Tabs ACR Siemens Found? # data channels (N) Data channels Routine/Scan Tabs A: Table Increment Feed (Seq. scans only) Scan Tab H: Table Speed Feed per Rotation (Spiral scans only) N x T x Pitch Pitch Pitch (Spiral scans only) Scan Tab Parameter Formula Example Z-coverage # detector rows x collimated slice width [N x T] 16 x 1.2 = 19.2 mm Feed per Rotation z-coverage x pitch [N x T x pitch]  (24 x 1.2) x 0.8p = 28.8mm x 0.8p = 23.04 mm/rot