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Posted 2006-12-03 22:47:33

Diagnostic accuracy of transesophageal echocardiography, helical computed tomography, and magnetic resonance imaging for suspected thoracic aortic dissection: systematic review and meta-analysis.

Shiga T, Wajima Z, Apfel CC, Inoue T, Ohe Y.

Department of Anesthesiology, Toho University Ohashi Medical Center, Tokyo, Japan. QZX02115@nifty.com

BACKGROUND: Patients with suspected thoracic aortic dissection require early and accurate diagnosis. Aortography has been replaced by less invasive imaging techniques including transesophageal echocardiography (TEE), helical computed tomography (CT), and magnetic resonance imaging (MRI); however, accuracies have varied from trial to trial, and which imaging technique should be applied to which risk population remains unclear. We systematically reviewed the diagnostic accuracy of these imaging techniques in patients with suspected thoracic aortic dissection. METHODS: Published English-language reports on the diagnosis of thoracic aortic dissection by TEE, helical CT, or MRI were identified from electronic databases. Sensitivity, specificity, and positive and negative likelihood ratios were pooled in a random-effects model. RESULTS: Sixteen studies involving a total of 1139 patients were selected. Pooled sensitivity (98%-100%) and specificity (95%-98%) were comparable between imaging techniques. The pooled positive likelihood ratio appeared to be higher for MRI (positive likelihood ratio, 25.3; 95% confidence interval, 11.1-57.1) than for TEE (14.1; 6.0-33.2) or helical CT (13.9; 4.2-46.0). If a patient had shown a 50% pretest probability of thoracic aortic dissection (high risk), he or she had a 93% to 96% posttest probability of thoracic aortic dissection following a positive result of each imaging test. If a patient had a 5% pretest probability of thoracic aortic dissection (low risk), he or she had a 0.1% to 0.3% posttest probability of thoracic aortic dissection following a negative result of each imaging test. CONCLUSION: All 3 imaging techniques, ie, TEE, helical CT, and MRI, yield clinically equally reliable diagnostic values for confirming or ruling out thoracic aortic dissection.

Posted 2006-12-03 22:30:31

From the FDA web site: Guidance for Industry, FDA Staff, and Third Parties. Provision for Alternate Measure of the Computed Tomography Dose Index (CTDI) to Assure Compliance with the Dose Information Requirements of the Federal Performance Standard for Computed Tomography

This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It does not create or confer any rights for or on any person and does not operate to bind FDA or the public. You can use an alternative approach if the approach satisfies the requirements of the applicable statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the appropriate number listed on the title page of this guidance.

Introduction

This document provides guidance to manufacturers and assemblers of x-ray computed tomography (CT) equipment and to FDA staff. Also, it serves as information for:

national and international organizations issuing safety and quality-assurance standards for CT equipment,

professional organizations concerned with radiation protection,

radiation safety personnel in the medical physics and health physics communities,

staff at clinical facilities reviewing the radiation dose-related specifications of CT equipment, and

physicians and x-ray technologists using CT equipment.

FDA is issuing this guidance to inform CT equipment manufacturers that it intends to exercise enforcement discretion, under certain circumstances, with respect to a specific provision of the U.S. Federal performance standard for computed tomography equipment (see the Code of Federal Regulations (CFR) at 21 CFR 1020.33). Specifically, FDA does not intend to object to the use of an alternate measure of the computed tomography dose index (CTDI). As discussed later in this document, CT equipment manufacturers who choose this alternative may substitute measured values of CTDI 100 for the required values of CTDI as defined in 21 CFR 1020.33(b)(1). No other provisions of the U.S. Federal performance standard are addressed in this guidance.

FDA's guidance documents, including this guidance, do not establish legally enforceable responsibilities. Instead, guidances describe the Agency's current thinking on a topic and should be viewed only as recommendations, unless specific regulatory or statutory requirements are cited. The use of the word should in Agency guidances means that something is suggested or recommended, but not required.

The Least Burdensome Approach

We believe we should consider the least burdensome approach in all areas of medical device regulation. This guidance reflects our careful review of the relevant scientific and legal requirements and what we believe is the least burdensome way for you to comply with those requirements. However, if you believe that an alternative approach would be less burdensome, please contact us so we can consider your point of view. You may send your written comments to the contact person listed in the preface to this guidance or to the CDRH Ombudsman. Comprehensive information on CDRH's Ombudsman, including ways to contact him, can be found on the Internet at http://www.fda.gov/cdrh/ombudsman/.

Background

New Aspects of CT Operation

Since the introduction of the concept of CTDI (Shope et al. 1981) and especially after FDA issued its formal regulatory definition in the Federal Register of August 31, 1984, advances in CT technology, practice, and radiation dosimetry have outpaced the accuracy of this quantity as an indicator of actual radiation dose and have weakened its relevance to clinical dose in patients (Dixon 2003). This situation is exacerbated by a widely held misperception of CTDI as an accurate measure of CT dose in individual patients and by its misappropriation for purposes of quality assurance and dose optimization in clinical practice (Brenner 2005). In fact, the quantity CTDI is an index which provides only an indication of the magnitude of doses that would be delivered to patients and of the changes in doses as a function of CT scanner model and conditions of operation. CTDI approximates the average central dose value associated with a spatially complex dose distribution in a reference acrylic dosimetry phantom for one particular set of exam techniques, i.e., those employing multiple, contiguous fan-beam scans in axial-scanning mode with fixed values of the x-ray tube current. Over the years, however, helical scanning, simultaneous acquisition of multiple tomographic sections, automatic exposure control, and cone-beam irradiation and detection geometry all developed as important new aspects of CT operation well beyond the scope of the axial-scanning mode appropriate for evaluation of CTDI.

Range of Mathematical Integration

In particular, as spatial resolution improved to accommodate imaging of tomographic sections significantly narrower than the 10-mm thick slices typical of CT systems and practice in the 1980s, the relatively short range of mathematical integration of CTDI in 21 CFR 1020.33(b)(1) limited the ability of CTDI to adequately account for contributions to dose from radiation scattered beyond that finite integration range.

Standardization

One response to these limitations was the adaptation by the medical physics community of the quantity CTDI 100 (and related variants), evaluated with a fixed-length (100 mm) “pencil” ionization chamber, as a more practicably measurable dose index (Leitz et al. 1995) and relatively more realistic indication of dose than the CFR-defined CTDI (21 CFR 1020.33(b)(1)) (Jessen et al. 1999). For measurements in the center of dosimetry phantoms, values of CTDI 100 are larger than those of CTDI by factors ranging from 2.6 to 1.0 for slice thicknesses ranging from 2 mm to 10 mm, respectively (Jessen et al. 1999). The adaptation of CTDI 100 was eventually standardized by the International Electrotechnical Commission (IEC 2002) and has been adopted by CT manufacturers and regulatory authorities internationally.

Advantages of CTDI 100

Although CTDI 100 in itself addresses few of the shortcomings of CTDI as a representation of dose to an actual patient, CTDI 100 has been a practical step forward from CTDI as defined in the CFR. When applied as intended to benchmark characteristic doses of different CT models operating in a conventional axial-scanning mode, either CTDI or CTDI 100 serves the same purpose. Either quantity in itself continues to be a useful, although narrow, means for comparison of relative dose efficiency scanner-to-scanner. However, CTDI 100 is much more broadly measured and applied than CTDI. More importantly, CTDI 100 also serves as the basis parameter in the evaluation of derivative indices used to refine the characterization of dose in CT. These latter indices are the weighted computed tomography dose index (CTDI w), the volume computed tomography dose index (CTDI vol), and the dose-length product (DLP) (European Commission 2004). Scanners complying with the current international safety standard for CT equipment display values of CTDI vol on their control panels (IEC 2002). Furthermore, CTDI vol and DLP are likely to be included in a CT standardized dose reporting module of the Digital Imaging and Communications in Medicine (DICOM) standard in the near future.

Recommendations for Harmonization

The National Conference on CT Dose Reduction, conducted in 2002 by the National Council on Radiation Protection and Measurements (NCRP), recommended standardization of CT dose terminology following input from a variety of national and international organizations concerned with standardization and radiation protection, including the National Electrical Manufacturers Association (NEMA) and the IEC (Linton and Mettler 2003). The recommendation to harmonize the U.S. Federal performance standard with standards of the IEC was echoed in meetings of the NEMA CT group with FDA staff in July 2003 and April 2004 as well as in follow-up correspondence.

Benefits

The substitution of CTDI 100 for CTDI will save manufacturers time and expense, with no reduction in safety, efficacy, or quality assurance of the equipment, because only one set of measurement values need be taken and provided to users to assure compliance with U.S. and international standards.

Use of CTDI 100

FDA intends to exercise enforcement discretion when CT equipment manufacturers substitute measured values of CTDI 100 for the required values of CTDI to meet the dose information requirements of the U.S. Federal performance standard at 21 CFR 1020.33(c)(2), if:

the manufacturer’s substituted values meet the definition of CTDI 100 described below

AND

the manufacturer clearly identifies the substituted values as CTDI 100 values rather than CTDI values.

Definition

Computed tomography dose index 100 (CTDI 100) means the integral of the dose profile along a line perpendicular to the tomographic plane divided by the product of the nominal tomographic section thickness and the number of tomograms produced in a single axial scan; that is:

where:

z = position along a line perpendicular to the tomographic plane.

D(z) = dose in air at position z of the dosimetry phantom.

T = nominal tomographic section thickness.

n = number of tomograms produced in a single scan.

This definition includes the following aspects:

(1) It is assumed that the dose profile is centered on z = 0.

(2) Although D(z) is to be measured in a dosimetry phantom defined in 21 CFR 1020.33(b)(6) as made of polymethyl methacrylate (PMMA), dose is to be reported in terms of absorbed dose in air, not in terms of absorbed dose in PMMA. In this definition of CTDI 100, air serves as a reference medium while the PMMA dosimetry phantom serves as the actual material matrix within which measurements are made. (Note that this method of evaluation of CTDI 100 is contrary to that of CTDI, where D(z) is evaluated and reported as dose in PMMA.)

(3) For a multiple tomogram system, the scan increment between adjacent scans is assumed to be nT. When the scan increment between adjacent scans does not equal nT, an adjustment is to be made and explained in the user information. For example, for a CT scanner operating in a mode of overlapping tomographic sections such as that associated with a “flying focal spot,” it is assumed that the value of the product nT will be adjusted to account for the overlap.

CT-related terms used but not explicitly defined or explained in the preceding definition carry the same meanings as corresponding terms defined in 21 CFR 1020.33(b).

References

Brenner DJ. “Is it time to retire the CTDI for CT quality assurance and dose optimization?” Letter to the Editor, Medical Physics Vol. 32, No. 10, pp. 3225-3226, October 2005.

Code of Federal Regulations (21 CFR 1020.33) . “Computed tomography (CT) equipment,” April 1, 2006, http://a257.g.akamaitech.net/7/257/2422/10apr20061500/edocket.access.gpo.gov/cfr_2006/aprqtr/pdf/21cfr1020.33.pdf.

Dixon RL. “A new look at CT dose measurement: Beyond CTDI,” Medical Physics Vol. 30, No. 6, pp. 1272-1280, June 2003.

European Commission. 2004 CT Quality Criteria, http://www.msct.info/CT_Quality_Criteria.htm.

Federal Register . “Diagnostic X-Ray Systems and Their Major Components; Amendments to Performance Standard,” August 31, 1984 (64 FR 34698).

International Electrotechnical Commission. International Standard IEC 60601-2-44 Edition 2.1, Medical electrical equipment – Part 2-44: Particular requirements for the safety of X-ray equipment for computed tomography, November 2002.

Jessen KA, Shrimpton PC, Geleijns J, Panzer W, and Tosi G. “Dosimetry for optimisation of patient protection in computed tomography,” Applied Radiation and Isotopes Vol. 50, No. 1, pp. 165-172, January 1999.

Leitz W, Axelsson B, Szendrö G, “Computed tomography dose assessment: A practical approach,” Radiation Protection Dosimetry Vol. 57, pp. 377-380, 1995.

Linton OW and Mettler, Jr., FA. “Opinion. National Conference on Dose Reduction in CT, with an Emphasis on Pediatric Patients,” American Journal of Roentgenology Vol. 181, pp. 321-329, August 2003.

Shope TB, Gagne RM, and Johnson GC. “A method for describing the doses delivered by transmission x-ray computed tomography,” Medical Physics Vol. 8, No. 4, pp. 488-495, July/August 1981.

Posted 2006-11-30 13:32:46

CHICAGO -- In a new twist on the slogan “milk does a body good,” radiologists are testing use of the dairy staple as a contrast agent in gastrointestinal imaging exams—with excellent results. The researchers reported their findings today at the annual meeting of the Radiological Society of North America (RSNA).

“We are able to achieve similar bowel distension and enhancement as we see with the commonly used contrast agent, VoLumen,” said Lisa R. Shah-Patel, M.D., a radiology resident at St. Luke’s-Roosevelt Hospital in New York City. “In addition, we found that patients are more willing to drink milk because it is part of their daily lives, and they know what to expect.”

Computed tomography (CT) imaging of the gastrointestinal tract is often done for abdominal pain. When the condition calls for visualization of the small intestinal wall, a negative oral contrast agent should be used. VoLumen is a barium-based oral contrast agent that works with intravenous contrast to allow better visualization of the bowel wall and clearer delineation between the bowel cavity and soft tissue.

When milk is used, the milk-filled intestinal cavity appears dark, while the intestinal wall appears bright due to intravenous contrast enhancement. The dark intestinal cavity contrasting with the bright intestinal wall makes any evidence of disease on the bowel wall more visible.

The researchers studied 179 adult patients undergoing CT with oral and intravenous contrast for abdominal discomfort to compare cost effectiveness and patient tolerance for whole milk versus VoLumen. Sixty-two patients received VoLumen, and 117 received milk. Of the 57 VoLumen patients who completed a subsequent questionnaire, 24 (42 percent) experienced abdominal discomfort such as cramps, diarrhea and nausea, while only 27 (23 percent) of the 117 patients who received milk reported abdominal discomfort.

Overall, milk was found to be just as effective as VoLumen in bowel distension (expansion) and bowel-wall conspicuity (enhancement). One important difference is the price. VoLumen costs $18 per patient, while whole milk costs $1.39 per patient.

“There are several advantages to milk. Patients are more willing to drink milk than VoLumen, and it costs a fraction of the price,” Dr. Shah-Patel said. “We hope that substituting milk for other contrast agents will reduce the number of people who refuse imaging tests because they do not want to drink the oral contrast, especially children.”

Co-authors are Chi Wan Koo, M.D., Jeanne W. Baer, M.D., and David H. Frager, M.D.

Posted 2006-11-30 13:30:44

Vik S posted: Earlier, the diagnosis of kidney stones did not involve information regarding the fragility of the stones. This made it impossible to determine the intensity and number of shock waves required during Lithotripsy to disintegrate the stone. Many patients would end up receiving more shock waves than was necessary to break up their stones. To regulate the use of SWL, investigators have found that computed tomography (CT) images of kidney stones can reveal significant internal structure in stones--structure that is likely to be useful in predicting stone fragility.

The Indiana Kidney Stone Institute in collaboration with Indiana University School of Medicine and National Kidney Foundation of Indiana sponsored a study to determine whether available clinical helical CT is able to reveal internal structure of kidney stones. Forty candidates, above 18 years of age, men as well as women, were enrolled in the study in July 2002, to be followed up till February 2006.

Eligibility was based on the ability to suspend respiration for at least 20 seconds, and those needing a computed tomography scan prior to their stone surgical treatment. Pregnant women and candidates with a history of abdominal malignancy were excluded.

Although, Helical computed tomography was commonly used in the assessment and treatment of kidney stone patients, its full potential to differentiate among stone types by structure or radiodensity was yet to be realized. CT scans were usually conducted only to identify the existence of the stone and to indicate its size and location. The use of soft tissue windows failed to reveal the structure within the kidney stone.

Treatment of Kidney stones is dependant on three factors- the type, size and location of the kidney stone. Shock wave Lithotripsy is used to break down stones into gravel that may be naturally removed from the body. However, shock waves may not be ideal to break down certain stones, or due to the complicated location of a stone it may have to be removed through more invasive surgical means. In addition, SWL is not without complications with long-term risks of hypertension and renal insufficiency.

Also, kidney stones vary in their SWL fragility. With the continuous advancement of technology for clinical CT, the latest generation of multidetector helical CT machines has considerably improved image resolution over single-detector CT technology. These quad-slice scanners have 4 contiguous, parallel rows of x-ray detectors combined with a higher gantry rotation speed which increase the speed of data collection by a factor as high as 8 over the conventional single-slice spiral CT scanners.

The latest technology makes for higher spatial resolution along the longitudinal axis of the patient. The scans can also be performed much faster, which means improved temporal resolution and less motion artifacts. Thus, CT scan has the ability to both predict stone composition and delineate structural features necessary to predict stone fragility to lithotripter shock waves.

Posted 2006-11-24 04:43:55

Chelmsford, Mass.-based Mercury Computer Systems, a provider of computing systems and software for data-intensive applications is teaming with the Institute of Medical Physics (IMP) of Erlangen, Germany to utilize the IBM/Toshiba/Sony-developed Cell Broadband Engine (BE) processor,

The Cell BE processor contains eight synergistic processing elements with peak performance in excess of 180 GFLOPS (180 billion floating-point operations per second) with a 25GBps memory bandwidth.

They estimate that CT scan reconstructions can be increase 100 times the current speed of microprocessor-based reconstructions.

Posted 2006-11-24 00:51:42

Multidetector CT scanner speeds diagnosis and treatment of patients. One of its many uses is to perform CT coronary angiography. Multidetector CT has generated excitement within the cardiology and radiology community as it provides clear pictures and takes less time than other non-invasive techniques, including conventional spiral and electron-beam CT which can take up to an hour or more. This atlas presents over 160 illustrations, with 116 in color and illustrates the capacity of multidetector CT for the analysis of the anatomy of the coronary arteries.

Posted 2006-11-24 00:49:23

phoenix|x-ray announced that it has been awarded theGlobal Technology Award 2006 in the category “Best Inspection/X-ray system” for its novel 160kV nanofocus® computed tomography system nanotom®. The award was presented by Global SMT & Packaging Magazine during Assembly Technology Expo in Rosemont, Chicago.

The compact system consists of a granite base, a 160-kV high-power nanofocus X-ray tube, and a digital detector with 5-Megapixel resolution. The nanotom to analyze samples that are up to 120 mm (4.7 in.) in diameter and weigh up to 1 kg (2.2 lbs) with voxel-resolution of less than 500 nm (0.5 microns).

Posted 2006-11-24 00:36:38

Article reviews the clinical and imaging clearance of the thoracic and lumbar spines of blunt trauma victims and the evolution of these strategies with the use of new imaging technologies.

A comprehensive literature search was performed, and articles identified were critically appraised.

Twenty papers were identified, 12 directly comparing computed tomography screening with plain X-rays. Evidence-based protocols are presented. The evolution of imaging strategies in response to new technology is described.

Thoracolumbar spine screening is best done using reformatted images acquired when scanning the chest and abdomen of high-risk multi-trauma patients. If computed tomography is not clinically indicated for investigation of other injuries then plain films are the first line investigation.

Posted 2006-11-21 12:28:23

A preliminary study suggests that high-resolution computed tomography (CT) modeling allows surgeons to custom-design acrylic implants prior to reconstructive surgery for patients with severe defects in their faces and eye cavities. Such implants appear to offer excellent aesthetic results and are well tolerated over the long term, according to a report in the November/December issue of Archives of Facial Plastic Surgery, one of the JAMA/Archives journals.

Posted 2006-11-21 12:13:24

The team used modern forensic techniques to confirm it was scurvy that doomed the men. Using an advanced form of CT scan called multidetector computed tomography, they studied bones of six of the settlers. The scans revealed evidence of skeletal lesions and bleeding into the joints and bones, telltale signs of the disease.

Posted 2006-11-21 12:08:10

This podcast discusses cutting edge research in CT scanning (computed tomography) and is aimed at radiologists, radiology technologists, and other healthcare professionals. Free registration required.

Posted 2006-11-21 12:03:22

A study using computed tomography to image the cervical spine and identify which radiographic findings predict failure of non-operative treatment.

Posted 2006-11-14 20:17:52

Three-dimensional computed tomography colonography, also known as virtual colonoscopy, is an accurate screening method for colorectal cancer, according to a study published in the November issue of the journal Radiology.

Posted 2006-11-03 12:00:10

The diagnostic accuracy of 64-slice CTCA for ruling out the presence of significant coronary stenoses in patients undergoing valve surgery is excellent and allows CTCA implementation as a gatekeeper for invasive CCA in these patients.

Posted 2006-11-03 00:23:08

The results of a clinical study comparing Isovue®-370 (iopamidol injection), marketed by Bracco Diagnostics Inc. in the United States, and Visipaque™-320 (iodixanol injection), marketed by GE Healthcare in the United States, in renally Impaired Patients undergoing Computed Tomography (IMPACT) showed no significant difference in the rate of contrast-induced nephropathy (CIN) between the two agents.

Posted 2006-11-03 00:15:18

Discusses methods for diagnosing asbestos lung disease and mesothelioma and the usefulness of CT.

Posted 2006-11-03 00:05:07

A new study published in JAMA found that a multidetector computed tomography (MDCT) scan, a "fifteen-seconds" heart imaging modality, can accurately identify those patients who are at the greatest risk for acute coronary syndrome.

Posted 2006-11-03 00:03:02

THE AMERICAN Heart Association (AHA) recently published a scientific statement on the utility and limitations of cardiac computed tomography (CT) systems for imaging of coronary heart disease (Circulation, October 17, 2006) after reviewing 245 scientific papers on the topic.

Posted 2006-11-02 23:24:13

In a finding that could change the landscape of lung cancer diagnosis and treatment, new research shows that annual screening using computed tomography (CT) detected lung tumors at their earliest stage in 85 percent of patients.

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© 1983-2006 Kevin M. Rosenberg, M.D.