Quantitating aortic regurgitation by cardiovascular magnetic resonance: significant variations due to slice location and breath holding.

OBJECTIVES: Compare variability in flow measurements by phase contrast MRI, performed at different locations in the aorta and pulmonary artery (PA) using breath-held (BH) and free-breathing (FB) sequences. METHODS: Fifty-seven patients with valvular heart disease, confirmed by echocardiography, were scanned using BH technique at 3 locations in the ascending aorta (SOV = sinus of Valsalva, STJ = sinotubular junction, ASC = ascending aorta at level of right pulmonary artery) and 2 locations in PA. Single FB measurement was obtained at STJ for aorta. Obtained metrics (SV = stroke volume, FV = forward volume, BV = backward volume, RF = regurgitant fraction) were evaluated separately for patients with aortic regurgitation (AR, n = 31) and mitral regurgitation (n = 26). RESULTS: No difference was noted between the two measurements in the PA. Significant differences were noted in measured SV at different aortic locations. SV measurements obtained at ASC correlated best with the measurements obtained in the PA. Strongest correlation of AR was measured at the STJ. CONCLUSION: Measurements of flow volumes by phase contrast MRI differ depending on slice location. When using stroke volumes to calculate pulmonary to systemic blood flow ratio (Qp/Qs), ASC should be used. For quantifying aortic regurgitation, measurement should be obtained at STJ. KEY POINTS: • Aortic regurgitation can be accurately measured by MRI. • Aortic regurgitation measurement by MRI varies according to the location where measured. • Aortic regurgitation can also be measured by MRI without breath hold.

MR lymphangiography: How i do it.

Lymphedema is a chronic progressive edematous disease that in the United States is most commonly related to malignancy and its treatment. Lymphaticovenular anastomosis is a recently introduced microsurgical treatment option for lymphedema that requires the identification and mapping of individual lymphatic channels. While nuclear medicine lymphoscintigraphy has been the primary imaging modality performed to evaluate suspected lymphedema, lymphoscintigraphy does not provide the spatial information necessary for presurgical planning. High-resolution dynamic 3D magnetic resonance imaging (MRI) can noninvasively image abnormal lymphatic channels to both diagnose lymphedema and depict the location and number of individual lymphatic channels for surgical planning. MR lymphangiography can be performed at 1.5T or 3.0T using multichannel phased array surface coils. The main components of the exam are a heavily T2 -weighted 3D sequence to define the severity and extent of edema, a high-resolution dynamic 3D gradient echo imaging after intracutaneous contrast injection to visualize lymphatic channels, and a delayed 3D gradient echo sequence after intravenous contrast to define veins. This article reviews the pathophysiology and microsurgical treatment of lymphedema, presents the imaging protocol used at our institution, and describes exam interpretation and the image postprocessing performed for surgical planning.

Dual energy computed tomography quantification of carotid plaques calcification: comparison between monochromatic and polychromatic energies with pathology correlation.

PURPOSE: We compared carotid plaque calcification detection sensitivity and apparent cross-sectional area on CT as a function of CT beam energy using conventional CT techniques and virtual mono-energetic CT images generated from dual-energy acquisitions. METHODS & MATERIALS: Five ex-vivo carotid endarterectomy (CEA) specimens were imaged with dual-energy computed tomography. Virtual monochromatic spectrum (VMS) CT images were reconstructed at energies between 40-140 keV. The same specimens were imaged using conventional polyenergetic spectrum (PS) CT with peak beam energies 80, 100, 120, and 140 kVp. The histological calcium areas on each corresponding CEA specimen were traced manually on digitized images of Toluidine-Blue/Basic-Fuchsin stained plastic sections. RESULTS: 40 keV VMS CT images provided high detection sensitivity (97 %) similar to conventional PS CT images (~96 %). The calcification size measured on CT decreased systematically with increasing CT beam energy; the rate of change was larger for the VMS images than for PS images. CONCLUSION: From a single dual-energy CT, multiple VMS-CT images can be generated, yielding equivalent detection sensitivity and size correlations as conventional PS-CT in CEA calcification imaging. VMS-CT at 80-100 keV provided the most accurate estimates of calcification size, as compared to histology, but detection sensitivity was reduced for smaller calcifications on these images. KEY POINTS: • Calcifications depicted at 80-100 keV were most similar to the histology standard. • Conventional polychromatic images demonstrated excellent correlation with plaque size at pathology. • Conventional polychromatic images systematically overestimate plaque size. • Plaque calcifications can be missed on high energy monochromatic images.

Enhancement of the pulmonary arteries and thoracic aorta: comparison of a biphasic contrast injection and fixed delay protocol with a monophasic injection and a timing bolus protocol.

The definitive diagnosis of pulmonary embolism, a significant cause of morbidity and mortality, relies on imaging. In this study, we compare the conventional computed tomography pulmonary angiogram (CTPA) protocol to a double-rule out CT angiogram (DRO CTA) protocol in terms of vascular enhancement, radiation dose, and contrast volume delivered. The CTPA protocol involves injection of a timing bolus for localization of the pulmonary artery, whereas the DRO CTA protocol involves a biphasic contrast. We analyzed 248 consecutive CTPA studies and 242 consecutive DRO CTA studies. Vessel enhancement using region of interest (ROI) measurements, radiation dose delivered, and total contrast volume administered was recorded. The enhancement of all vessels measured was statistically significantly higher with the biphasic DRO CTA protocol than the CTPA protocol. The difference in mean vascular enhancement for the two protocols was greatest in the descending aorta (DA, P < 0.001) and least in the main pulmonary artery (MPA, P = 0.001). The percent of studies with vascular enhancement ≥250 Hounsfield units (HU) was significantly greater in all vascular beds except the MPA when the DRO CTA protocol was used. Studies performed with the DRO CTA protocol led to less radiation exposure and used less contrast than those performed with the CTPA protocol (P < 0.001 for both). According to the final radiology report, 35.08 % of studies in the CTPA group and 22.31 % of studies in the DRO CTA group were considered indeterminate (P = 0.001). In conclusion, the biphasic DRO CTA protocol leads to statistically significantly higher opacification of all pulmonary arterial and aortic vessels studied, with no greater delivery of radiation or contrast, than the monophasic CTPA protocol.

Standard and reduced radiation dose liver CT images: adaptive statistical iterative reconstruction versus model-based iterative reconstruction-comparison of findings and image quality.

PURPOSE: To investigate whether reduced radiation dose liver computed tomography (CT) images reconstructed with model-based iterative reconstruction ( MBIR model-based iterative reconstruction ) might compromise depiction of clinically relevant findings or might have decreased image quality when compared with clinical standard radiation dose CT images reconstructed with adaptive statistical iterative reconstruction ( ASIR adaptive statistical iterative reconstruction ). MATERIALS AND METHODS: With institutional review board approval, informed consent, and HIPAA compliance, 50 patients (39 men, 11 women) were prospectively included who underwent liver CT. After a portal venous pass with ASIR adaptive statistical iterative reconstruction images, a 60% reduced radiation dose pass was added with MBIR model-based iterative reconstruction images. One reviewer scored ASIR adaptive statistical iterative reconstruction image quality and marked findings. Two additional independent reviewers noted whether marked findings were present on MBIR model-based iterative reconstruction images and assigned scores for relative conspicuity, spatial resolution, image noise, and image quality. Liver and aorta Hounsfield units and image noise were measured. Volume CT dose index and size-specific dose estimate ( SSDE size-specific dose estimate ) were recorded. Qualitative reviewer scores were summarized. Formal statistical inference for signal-to-noise ratio ( SNR signal-to-noise ratio ), contrast-to-noise ratio ( CNR contrast-to-noise ratio ), volume CT dose index, and SSDE size-specific dose estimate was made (paired t tests), with Bonferroni adjustment. RESULTS: Two independent reviewers identified all 136 ASIR adaptive statistical iterative reconstruction image findings (n = 272) on MBIR model-based iterative reconstruction images, scoring them as equal or better for conspicuity, spatial resolution, and image noise in 94.1% (256 of 272), 96.7% (263 of 272), and 99.3% (270 of 272), respectively. In 50 image sets, two reviewers (n = 100) scored overall image quality as sufficient or good with MBIR model-based iterative reconstruction in 99% (99 of 100). Liver SNR signal-to-noise ratio was significantly greater for MBIR model-based iterative reconstruction (10.8 ± 2.5 [standard deviation] vs 7.7 ± 1.4, P < .001); there was no difference for CNR contrast-to-noise ratio (2.5 ± 1.4 vs 2.4 ± 1.4, P = .45). For ASIR adaptive statistical iterative reconstruction and MBIR model-based iterative reconstruction , respectively, volume CT dose index was 15.2 mGy ± 7.6 versus 6.2 mGy ± 3.6; SSDE size-specific dose estimate was 16.4 mGy ± 6.6 versus 6.7 mGy ± 3.1 (P < .001). CONCLUSION: Liver CT images reconstructed with MBIR model-based iterative reconstruction may allow up to 59% radiation dose reduction compared with the dose with ASIR adaptive statistical iterative reconstruction , without compromising depiction of findings or image quality.

Dual-energy liver CT: effect of monochromatic imaging on lesion detection, conspicuity, and contrast-to-noise ratio of hypervascular lesions on late arterial phase.

OBJECTIVE: The purpose of this study was to evaluate the effect of use of dual-energy CT monochromatic imaging in the late hepatic arterial phase on hyperenhancing focal lesion detection and lesion conspicuity. SUBJECTS AND METHODS: This prospective study included 72 patients imaged with a single-source dual-energy CT scanner. Late arterial phase imaging was performed with dual energies of 140 and 80 kVp, and the portal venous and delayed phases were performed with a single energy of 120 kVp. Two deidentified image sets were created: set A consisted of 77-keV images only, and set B consisted of 40-, 50-, 70-, and 77-keV images and iodine-based contrast material decomposition images. Two independent reviewers identified hypervascular lesions and subjectively scored lesion conspicuity. Contrast-to-noise ratios were calculated, and radiation dose (volume CT dose index) was recorded. RESULTS: The 128 lesions identified had a mean size of 1.7 ± 1.4 cm. There was no difference in lesion detection between the two reviewers or the two image sets. The contrast-to-noise ratio at 50 keV was 72% greater than that at 77 keV (p < 0.0001). Subjective conspicuity was statistically greatest at 50 keV (p < 0.0001). There was no statistical difference in mean volume CT dose index between the dual-energy (12.8 mGy) and the two single-energy (14.4 and 14.2 mGy) phases. CONCLUSION: Viewing dual-energy CT images may result in the greatest subjective lesion conspicuity and measured contrast-to-noise ratio at 50 keV with equal detection of hyperenhancing liver lesions compared with viewing 77-keV images alone. In addition, the radiation doses of dual-energy CT may be similar to those of single-energy CT.

Changes in measured size of atherosclerotic plaque calcifications in dual-energy CT of ex vivo carotid endarterectomy specimens: effect of monochromatic keV image reconstructions.

OBJECTIVE: The aim of this study was to compare the size of the calcifications measured on the different keV images to a histological standard. METHODS: Five ex vivo carotid endarterectomy (CEA) specimens were imaged with a dual-energy CT. CT images were reconstructed at different monochromatic spectral energies (40, 60, 77, 80, 100, 120, 140 keV). Cross-sectional area of the plaque calcifications present on each CT image was measured. The histological calcium areas on each corresponding CEA specimen were traced manually on digitised images of Toluidine Blue/Basic Fuchsin stained plastic sections. The CT images and corresponding histology sections were matched. The CT-derived calcium areas on each keV image were compared to the calcified area measurements by histology. RESULTS: A total of 107 histology sections were matched to corresponding CT images. The average calcified area per section by histology was 7.6 ± 7 mm(2) (range 0-26.4 mm(2)). There was no significant difference between the calcified areas measured by histology and those measured on CT-virtual monochromatic spectral (VMS) reconstructed images at 77 keV (P = 0.08), 80 keV (P = 0.20) and 100 keV (P = 0.14). CONCLUSIONS: Calcium area measured on the 80 keV image set was most comparable to the amount of calcium measured by histology.

Evaluating contrast agent waste and costs of weight-based CT contrast bolus protocols using single- or multiple-dose packaging.

OBJECTIVE: Although weight-based contrast agent injection protocols can improve contrast-enhanced CT, one disadvantage is waste caused by differences between the amount of contrast material required for a weight-based algorithm and full-package protocols used with single-use packaging of contrast material. The availability of 500-mL multiple-use packaging of contrast material should facilitate the implementation of weight-based contrast bolus protocols for CT because arbitrary volumes of contrast agent can be loaded without significant waste. Our hypothesis was that multiple-use packaging when used with a weight-based contrast bolus protocol would reduce costs compared with single-use packaging. MATERIALS AND METHODS: Contrast agent volume loaded and volume actually delivered to 1304 patients undergoing abdominal and pelvic CT were recorded. Model 1 used volume loaded to estimate contrast material cost, model 2 used volume delivered, and model 3 assumed that patients received either 100 or 150 mL from a single-use package, depending on weight. RESULTS: Model 1 required 368 packages of 500 mL contrast material ($23,000). Model 2 required 353 packages of 500 mL contrast material ($22,062.50). Model 3 required 863 and 478 packages of 100 and 150 mL contrast material, respectively ($22,120). CONCLUSION: Cost containment can be realized while improving the quality of contrast opacification by employing 500-mL multiple-use packaging of contrast materials. Care must be taken by the technologists to load only the volume of contrast agent that is needed, or the resulting contrast agent waste will negate the savings and even result in cost increases.

Diagnostic performance of resting CT myocardial perfusion in patients with possible acute coronary syndrome.

OBJECTIVE: Coronary CT angiography has high sensitivity, but modest specificity, to detect acute coronary syndrome. We studied whether adding resting CT myocardial perfusion imaging improved the detection of acute coronary syndrome. SUBJECTS AND METHODS: Patients with low-to-intermediate cardiac risk presenting with possible acute coronary syndrome received both the standard of care evaluation and a research thoracic 64-MDCT examination. Patients with an obstructive (> 50%) stenosis or a nonevaluable coronary segment on CT were diagnosed with possible acute coronary syndrome. CT perfusion was determined by applying gray and color Hounsfield unit maps to resting CT angiography images. Adjudicated patient diagnoses were based on the standard of care and 3-month follow-up. Patient-level diagnostic performance for acute coronary syndrome was calculated for coronary CT, CT perfusion, and combined techniques. RESULTS: A total of 105 patients were enrolled. Of the nine (9%) patients with acute coronary syndrome, all had obstructive CT stenoses but only three had abnormal CT perfusion. CT perfusion was normal in all other patients. To detect acute coronary syndrome, CT angiography had 100% sensitivity, 89% specificity, and a positive predictive value of 45%. For CT perfusion, specificity and positive predictive value were each 100%, and sensitivity was 33%. Combined cardiac CT and CT perfusion had similar specificity but a higher positive predictive value (100%) than did CT angiography. CONCLUSION: Resting CT perfusion using CT angiographic images may have high specificity and may improve CT positive predictive value for acute coronary syndrome without added radiation and contrast. However, normal resting CT perfusion cannot exclude acute coronary syndrome.

Model-based iterative reconstruction versus adaptive statistical iterative reconstruction and filtered back projection in liver 64-MDCT: focal lesion detection, lesion conspicuity, and image noise.

OBJECTIVE: The purpose of this study is to compare three CT image reconstruction algorithms for liver lesion detection and appearance, subjective lesion conspicuity, and measured noise. MATERIALS AND METHODS: Thirty-six patients with known liver lesions were scanned with a routine clinical three-phase CT protocol using a weight-based noise index of 30 or 36. Image data from each phase were reconstructed with filtered back projection (FBP), adaptive statistical iterative reconstruction (ASIR), and model-based iterative reconstruction (MBIR). Randomized images were presented to two independent blinded reviewers to detect and categorize the appearance of lesions and to score lesion conspicuity. Lesion size, lesion density (in Hounsfield units), adjacent liver density (in Hounsfield units), and image noise were measured. Two different unblinded truth readers established the number, appearance, and location of lesions. RESULTS: Fifty-one focal lesions were detected by truth readers. For blinded reviewers compared with truth readers, there was no difference for lesion detection among the reconstruction algorithms. Lesion appearance was statistically the same among the three reconstructions. Although one reviewer scored lesions as being more conspicuous with MBIR, the other scored them the same. There was significantly less background noise in air with MBIR (mean [± SD], 2.1 ± 1.4 HU) than with ASIR (8.9 ± 1.9 HU; p < 0.001) or FBP (10.6 ± 2.6 HU; p < 0.001). Mean lesion contrast-to-noise ratio was statistically significantly higher for MBIR (34.4 ± 29.1) than for ASIR (6.5 ± 4.9; p < 0.001) or FBP (6.3 ± 6.0; p < 0.001). CONCLUSION: In routine-dose clinical CT of the liver, MBIR resulted in comparable lesion detection, lesion characterization, and subjective lesion conspicuity, but significantly lower background noise and higher contrast-to-noise ratio compared with ASIR or FBP. This finding suggests that further investigation of the use of MBIR to enable dose reduction in liver CT is warranted.

Cardiac complications of oncologic therapy.

As survival rates continue to increase for patients with childhood and adult malignancies, imaging utilization in these patients will likely increase substantially. It is important to detect disease recurrence and to recognize the potential complications that occur after treatment with oncologic medications and therapeutic radiation. The most common cardiotoxic side effect of the anthracycline drug class is a dose-dependent decline in ejection fraction, which may result in dilated cardiomyopathy. Multiple-uptake gated acquisition (MUGA) scanning plays an important role in diagnosis of this subclinical cardiac dysfunction. Other less common cardiotoxic side effects of chemotherapeutic medications include arrhythmia, myocarditis, coronary artery disease, tamponade, pericarditis, and pericardial effusion. Radiation therapy can also lead to cardiotoxicity when the heart or pericardium is included in the radiation portal. Radiation-induced conditions include pericardial disease, coronary artery disease, valvular disease, and cardiomyopathy. Many of these side effects are asymptomatic until late in the course of the disease. With imaging, these pathologic conditions can often be diagnosed before symptom onset, which may allow early intervention. Radiologists should be familiar with the current knowledge and pathophysiology regarding cardiac complications related to chemotherapy and radiation therapy of malignant neoplasms and the appearances of treatment-related cardiotoxicity that can be found at radiography, nuclear medicine examinations, and cross-sectional imaging. Supplemental material available at http://radiographics.rsna.org/lookup/suppl/doi:10.1148/rg.336125005/-/DC1.

Challenges to protocol optimization due to unexpected variation of CT contrast dose amount and flow.

High-quality computed tomography (CT) exams are critical to maximizing radiologist's interpretive ability. Exam quality in part depends on proper contrast administration. We examined injector data from consecutive abdominal and pelvic CT exams to analyze variation in contrast administration. Discrepancies between intended IV contrast dose and flow rate with the actual administered contrast dose and measured flow rate were common. In particular, delivered contrast dose discrepancies of at least 10% occurred in 13% of exams while discrepancies in flow rate of at least 10% occurred in 42% of exams. Injector logs are useful for assessing and tracking this type of variability which may confound contrast administration optimization and standardization efforts.

Impact of intraoperative fluoroscopic beam positioning relative to the hip and pelvis on perceived acetabular component position.

Background: Parallax is poorly understood and can mislead surgeons using intraoperative fluoroscopy (IF) to guide cup placement during anterior approach (AA) total hip arthroplasty. The purpose of this study was to examine how changes in fluoroscopic beam positioning in relation to the hip and pelvis affects the projected acetabular image. Methods: An acetabular component was positioned in an anatomic pelvis model in 45° and 20° of abduction and anteversion, respectively using a computer assisted cup targeting system. Fluoroscopic images were taken at various caudal and cranially directed angles with the fluoroscopic beam centered over the hip then pelvis. In each position, four independent observers measured the abduction and anteversion angles of the projected cup image using the same computer targeting system. Results: Cup abduction and anteversion measured 43.5° and 19.5° when IF was centered over the hip and 40.5 and 27.5° when centered over the pelvis in the neutral position. Increasing the caudal direction of the beam 20° increased the projected abduction/anteversion angles by approximately 7°/12° and 9°/16° when centered over the hip and pelvis respectively. Increasing the cranial direction of the beam 20° decreased the measured abduction/anteversion angles by roughly 4°/20° and 4°/24° when centered over the hip and pelvis, respectively. Conclusion: The projected image of the acetabular component can change dramatically depending on fluoroscopic beam position relative to the hip and pelvis. Recognizing the approximate direction and magnitude of change with differing fluoroscopy positions may help surgeons avoid cup malpositioning.

Adaptive statistical iterative reconstruction versus filtered back projection in the same patient: 64 channel liver CT image quality and patient radiation dose.

OBJECTIVES: To compare routine dose liver CT reconstructed with filtered back projection (FBP) versus low dose images reconstructed with FBP and adaptive statistical iterative reconstruction (ASIR). METHODS: In this retrospective study, patients had a routine dose protocol reconstructed with FBP, and again within 17 months (median 6.1 months), had a low dose protocol reconstructed twice, with FBP and ASIR. These reconstructions were compared for noise, image quality, and radiation dose. RESULTS: Nineteen patients were included. (12 male, mean age 58). Noise was significantly lower in low dose images reconstructed with ASIR compared to routine dose images reconstructed with FBP (liver: p < .05, aorta: p < 0.001). Low dose FBP images were scored significantly lower for subjective image quality than low dose ASIR (2.1 ± 0.5, 3.2 ± 0.8, p < 0.001). There was no difference in subjective image quality scores between routine dose FBP images and low dose ASIR images (3.6 ± 0.5, 3.2 ± 0.8, NS).Radiation dose was 41% less for the low dose protocol (4.4 ± 2.4 mSv versus 7.5 ± 5.5 mSv, p < 0.05). CONCLUSIONS: Our initial results suggest low dose CT images reconstructed with ASIR may have lower measured noise, similar image quality, yet significantly less radiation dose compared with higher dose images reconstructed with FBP.

Utility of multiplanar and three-dimensional reconstructions from computed tomography performed for maternal indications for visualizing fetal anatomy and estimating gestational age.

OBJECTIVE: The purpose of this article was to determine the usefulness of multiplanar and 3-dimensional (3D) reconstructions of computed tomographic (CT) data from scans performed for maternal indications for visualizing fetal anatomy and estimating gestational age. MATERIALS AND METHODS: Eighteen pregnant patients who had abdominopelvic CT scanning performed for maternal indications formed the study group. Two independent reviewers created multiplanar and 3D-reconstructed images of the fetus from these CT scans and analyzed them for fetal anatomy and gestational age. Fetal dose estimates were also obtained. RESULTS: Computed tomographic fetal biometry generally agreed well with ultrasound estimates. Computed tomographic and ultrasound estimates were within 3 to 4 weeks of each other 95% of the time for the 2 reviewers. Pearson correlation coefficients were 0.989 for reviewer 1 and 0.985 for reviewer 2. Fetal anatomic survey revealed that it was easier to see bones and fluid-filled structures such as the stomach and urinary bladder than intracranial, intrathoracic, and intra-abdominal soft tissue structures. Estimated fetal dose was 28.5 (10.7) mGy using the Imaging Performance Assessment of CT Scanner calculator and 23.7 (7.7) mGy when taking maternal perimeter and fetal depth into account with the method of Angel et al. CONCLUSIONS: It is technically feasible to produce clinically useful images of the fetus using standard multiplanar reconstructions and 3D algorithms already in place for CT scanning. As CT scans continue to be performed under certain circumstances, particularly the emergency department setting, evaluation of maternal CT scans for potentially useful information about the fetus such as gestational age and gross anatomic survey can be obtained at estimated fetal radiation doses much lower than the actionable level of 150 mGy.

Negative ECG-gated cardiac CT in patients with low-to-moderate risk chest pain in the emergency department: 1-year follow-up.

OBJECTIVE: The purpose of this article is to determine the frequency of adverse cardiac events during the year following a negative cardiac CT angiogram in a population of patients presenting to the emergency department with low-to-moderate risk chest pain. SUBJECTS AND METHODS: Eighty-one consecutive patients who had standard of care evaluation for low-to-moderate risk chest pain in the emergency department were enrolled and consented to have a cardiac CT angiogram added to their workup and to have follow-up for 1 year. Eleven patients were excluded, six because their cardiac CT examinations were unsuccessful, four because of a positive cardiac CT angiogram result, and one was lost to follow-up. Seventy patients with negative cardiac CT angiographic results (< 50% stenosis) were included and were interviewed in detail at 3, 6, and 12 months about intervening cardiac events, diagnostic testing, and therapy. Electronic medical records were also reviewed at each time point. RESULTS: None of the 70 patients reported an adverse cardiac event over the 12-month follow-up period. At 1 year, the cause of chest pain was unknown in 49 patients, gastrointestinal in nine patients, anxiety in seven patients, musculoskeletal in three patients, and other in two patients. Three of four patients with 50% or greater stenosis on their cardiac CT had subsequent cardiac catheterization and stent placement. CONCLUSION: In patients with low-to-moderate risk chest pain evaluated in the emergency department, adverse cardiac events may be rare during the 12 months following a negative cardiac CT angiogram.

Triphasic contrast bolus for whole-chest ECG-gated 64-MDCT of patients with nonspecific chest pain: evaluation of arterial enhancement and streak artifact.

OBJECTIVE: The purpose of this study was to evaluate the use of a triphasic contrast bolus for ECG-gated CT in the assessment of chest pain by measuring vascular luminal attenuation and determining the degree of contrast-related streak artifact. MATERIALS AND METHODS: We reviewed the images from 44 ECG-gated CT examinations performed with a coronary contrast bolus modified for imaging of the entire chest. Luminal attenuation achieved with the resulting triphasic bolus was measured at specified vascular locations in the right side of the heart, pulmonary arteries, coronary arteries, and thoracic aorta. The occurrence of contrast-related streak artifact was recorded, and artifact severity was scored on a subjective 4-point scale. RESULTS: The mean attenuation values in the pulmonary arteries (345.3 +/- 136.7 HU), coronary arteries (340.8 +/- 82.5 HU), and thoracic aorta (386.4 +/- 67.2 HU) were above a diagnostic threshold of 200 HU. Although there was no significant difference between the mean arterial values, the right-heart attenuation (281.6 +/- 121.8 HU) was significantly lower than the attenuation in the other two locations. On a location basis, 92.2% of the 1,972 arterial measurements were above the 200-HU threshold. Streak artifacts were found in 21 examinations (47.7%), and none was scored as severe. Statistical analysis revealed that the occurrence of streak artifact increased with higher right-heart attenuation. CONCLUSION: In this series, a triphasic contrast bolus for ECG-gated whole-chest CT consistently achieved arterial attenuation above a diagnostic threshold in the pulmonary arteries, coronary arteries, and aorta. Right-heart attenuation was simultaneously reduced, which is important for decreasing the prevalence and severity of streak artifacts.

Image fusion as a new postprocessing method to evaluate the radiofrequency ablation zone after treatment of malignant liver tumors.

OBJECTIVE: We describe a manual segmentation and image fusion method to assess the relationship between liver tumors and the radiofrequency ablation zone depicted on cross-sectional imaging. CONCLUSIONS: Manual fusion of segmented images of hepatic tumors from a preprocedural scan with the ablation zone depicted on the postinterventional imaging examination may be used to create a composite image demonstrating the ablation margin. This technique may improve evaluation of the size of the ablation margin around the circumference of the tumor, thereby predicting which patients are more likely to incur local tumor recurrence.

Whole-chest 64-MDCT of emergency department patients with nonspecific chest pain: Radiation dose and coronary artery image quality with prospective ECG triggering versus retrospective ECG gating.

OBJECTIVE: The purpose of this study was to compare the patient radiation dose and coronary artery image quality of long-z-axis whole-chest 64-MDCT performed with retrospective ECG gating with those of CT performed with prospective ECG triggering in the evaluation of emergency department patients with nonspecific chest pain. SUBJECTS AND METHODS: Consecutively registered emergency department patients with nonspecific low-to-moderate-risk chest pain underwent whole-chest CT with retrospective gating (n = 41) or prospective triggering (n = 31). Effective patient radiation doses were estimated and compared by use of unpaired Student's t tests. Two reviewers independently scored the quality of images of the coronary arteries, and the scores were compared by use of ordinal logistic regression. RESULTS: Age, heart rate, body mass index, and z-axis coverage were not statistically different between the two groups. For retrospective gating, the mean effective radiation dose was 31.8 +/- 5.1 mSv; for prospective triggering, the mean effective radiation dose was 9.2 +/- 2.2 mSv (prospective triggering 71% lower, p < 0.001). Two of 512 segments imaged with retrospective gating were nonevaluable (0.4%), and two of 394 segments imaged with prospective triggering were nonevaluable (0.5%). Prospectively triggered images were 2.2 (95% CI, 1.1-4.5) times as likely as retrospectively gated images to receive a high image quality score for each segment after adjustment for segment differences (p < 0.05). CONCLUSION: For long-z-axis whole-chest 64-MDCT of emergency department patients with nonspecific chest pain, use of prospective ECG triggering may result in substantially lower patient radiation doses and better coronary artery image quality than is achieved with retrospective ECG gating.