Use Of Intravenous Contrast Material Research Articles

Strategies for improving colorectal cancer detection with routine computed tomography

To report the detection rate of colorectal tumors with computed tomography (CT) performed within 1year before diagnosis for indications other than colon abnormalities. Strategies to improve cancer detection are reported. Two board-certified, subspecialty-trained abdominal radiologists retrospectively reviewed patient health records and CT images with knowledge of tumor location/size. Patients were classified into 3 groups: prospective (colon abnormality suggesting neoplasm documented in radiologic report), retrospective (not documented in radiologic report but detected in our retrospective review of CT images), and undetected (neither prospectively nor retrospectively detected). Retrospective detection confidence and morphologic characteristics of each tumor were also recorded. Of 209 included patients, 106 (50.7%) had prospectively detected tumors, 66 (31.6%) had retrospectively detected tumors, and 37 (17.7%) had undetected tumors. Asymmetric bowel wall thickening and polypoid masses were present more often in the retrospective group than in the prospective group (27% vs. 10.5% and 26% vs. 17.1%, respectively). Tumors in the ascending colon were more likely to be detected retrospectively than prospectively (odds ratio, 2.75; 95% CI 1.07-7.08; P = 0.04). Undetected tumors were smaller on average (2.9cm) than prospective (6.0cm) and retrospective (4.9cm) tumors (P = 0.03). Detection confidence was lower for retrospectively detected tumors than for prospectively detected tumors (P = 0.03). Indications other than abdominal pain were most common for retrospectively detected tumors (P = 0.03). Use of intravenous contrast material was lowest in the undetected group (P = 0.003). The prospective group had more pericolonic abnormalities, regional/retroperitoneal lymph node involvement (P < 0.001), and distant metastases than did the retrospective group (P = 0.01). Half of all colorectal tumors were not detected prospectively. Radiologists should perform meticulous colon tracking regardless of the indication for CT. The right colon merits additional examination. Polypoid and asymmetric morphologic characteristics were most often overlooked, but these characteristics can be learned to improve detection.

Applications of Arterial Spin Labeling Sequence in Neuroimaging, Case Depictions with Examples: Case Series

Since many neurological diseases are associated with altered regional cerebral flow, Arterial Spin Labelling (ASL) image being a non invasive non contrast sequence, is increasingly being used and incorporated in routine protocols as an adjuvant sequence to study the regional alterations in cerebral perfusion or Cerebral Blood Flow (CBF). It demonstrates increased or decreased regional CBF in various brain pathologies reliably without the use of intravenous contrast material. In this series, ASL is increased (increased CBF) in cases of high-grade tumour, highly cellular tumours, encephalitis, tumour recurrence, acute phase of Posterior Reversible Encephalopathy Syndrome (PRES), and decreased in cerebral infarct, peri-infarct ischaemic penumbra, thereby making an effort to emphasise the significance and utilisation of ASL in adjunct to the other routine Magnetic Resonance Imaging (MRI) sequences.

Incidence and Risk Factors for Acute Kidney Injury After Chimeric Antigen Receptor T-Cell Therapy

ObjectiveTo evaluate the association of baseline and postinfusion patient characteristics with acute kidney injury (AKI) in the month after chimeric antigen receptor T-cell (CAR-T) therapy. MethodsWe retrospectively reviewed records of 83 patients with non-Hodgkin lymphoma undergoing CAR-T therapy (axicabtagene ciloleucel) between June 2016 and November 2020. Patients were followed up to 1 month after treatment. Post–CAR-T AKI was defined as a more than 1.5-fold increase in serum creatinine concentration from baseline (on the day of CAR-T infusion) at any time up to 1 month after CAR-T therapy. ResultsOf 83 patients, 14 (17%) developed AKI during follow-up. At 1 month after CAR-T infusion, 10 of 14 (71%) AKI events had resolved. Lower baseline estimated glomerular filtration rate, use of intravenous contrast material, tumor lysis prophylaxis, higher peak uric acid and creatine kinase levels during follow-up, and change in lactate dehydrogenase from baseline to peak level within 1 month after initiation of CAR-T therapy were significantly associated with AKI incidence during follow-up. Incidence of AKI was also higher in patients who received higher doses of corticosteroids and tocilizumab. ConclusionAcute kidney injury occurred in approximately 1 in 6 patients who received axicabtagene ciloleucel for non-Hodgkin lymphoma. Patients with high tumor burden receiving higher total doses of corticosteroids or tocilizumab should be closely monitored for development of AKI. Lower baseline kidney function at CAR-T initiation, exposure to contrast material, and progressive increase in levels of tumor lysis markers (uric acid, lactate dehydrogenase, creatine kinase) after CAR-T infusion may predict risk of AKI during the 1 month after infusion.

Deep Learning-based Detection of Intravenous Contrast Enhancement on CT Scans.

Identifying the presence of intravenous contrast material on CT scans is an important component of data curation for medical imaging-based artificial intelligence model development and deployment. Use of intravenous contrast material is often poorly documented in imaging metadata, necessitating impractical manual annotation by clinician experts. Authors developed a convolutional neural network (CNN)-based deep learning platform to identify intravenous contrast enhancement on CT scans. For model development and validation, authors used six independent datasets of head and neck (HN) and chest CT scans, totaling 133 480 axial two-dimensional sections from 1979 scans, which were manually annotated by clinical experts. Five CNN models were trained first on HN scans for contrast enhancement detection. Model performances were evaluated at the patient level on a holdout set and external test set. Models were then fine-tuned on chest CT data and externally validated. This study found that Digital Imaging and Communications in Medicine metadata tags for intravenous contrast material were missing or erroneous for 1496 scans (75.6%). An EfficientNetB4-based model showed the best performance, with areas under the curve (AUCs) of 0.996 and 1.0 in HN holdout (n = 216) and external (n = 595) sets, respectively, and AUCs of 1.0 and 0.980 in the chest holdout (n = 53) and external (n = 402) sets, respectively. This automated, scan-to-prediction platform is highly accurate at CT contrast enhancement detection and may be helpful for artificial intelligence model development and clinical application. Keywords: CT, Head and Neck, Supervised Learning, Transfer Learning, Convolutional Neural Network (CNN), Machine Learning Algorithms, Contrast Material Supplemental material is available for this article. © RSNA, 2022.

THE ROLE OF DIFFUSION WEIGHTED IMAGING IN DIFFERENTIATION BETWEEN BENIGN AND MALIGNANT OVARIAN LESIONS

• Ovarian carcinomas represent 6th most common cancer, the second most common gynecologic cancer and 4th leading cause of cancer death in women. With no viable screening estimates accessible, 70% of ovarian malignancies are diagnosed at a late stage. Separation of benign lesions from the malignant ones is of foremost significance to direct the correct clinical management. Imaging modalities, particularly ultrasonography (US), computed tomography (CT), and magnetic resonance (MR) imaging have become the first line for ovarian lesions diagnosis. • US remains the study of choice in the initial evaluation of suspected adnexal masses because it is relatively inexpensive, noninvasive, and widely available. Transabdominal US, endovaginal US, or both should be performed for the evaluation of adnexal masses. • MR imaging is a useful modality for differentiating benign and malignant ovarian tumors, and a specific diagnosis can be made for certain pathologic entities. Morphologic appearance, signal intensity characteristics, DWI and adequate use of intravenous contrast material provide information for arriving at the correct diagnosis.

Benefit of Contrast-Enhanced PET/CT versus Non-Contrast-Enhanced PET/CT Relative to Lesion Detection, Lesion Characterization, and Diagnostic Accuracy in Patients with Cancer

Objective: To investigate the benefit of contrast-enhanced PET/CT (PET/CECT) versus non-contrast-enhanced PET/CT (PET/NCCT) relative to lesion detection, characterization, and diagnostic accuracy in cancer patients. Materials and Methods: The present study was a prospective study that included patients older than 18 years with histopathologically proven cancer who underwent [F-18] fluorodeoxyglucose ([F-18]FDG) PET/CT at the Division of Nuclear Medicine, Department of Radiology, Faculty of Medicine, Siriraj Hospital between December 2014 and November 2017. PET/NCCT was performed followed by PET/CECT scan in all patients. The results of PET/NCCT, PET/CECT, and pre- and post-contrast enhanced PET/CT (PET/NCCT-CECT) for each patient were interpreted by one nuclear medicine physician and one radiologist. The sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV) were calculated from ROC curve analysis. Results: One hundred ten patients were included. The mean age was 52.45±17.14 years, and 52.7% were female. Lymphoma was the most common cancer diagnosis (47.3%). No significant difference was observed between PET/CT techniques for detection rate at the primary tumor site, lymph node, or distant organ. High agreement was observed between PET/CT techniques for lesion characterization. Lesion characterizations were not significantly correlated with age, gender, BMI, or FBS; however, lesion characterization was found to be significantly associated with primary tumor site, indication for PET/CT and lesion size. The following ranges were observed from all PET/CT techniques: sensitivity 81.5% to 85.3%, specificity 94.4% to 95.5%, accuracy 89.4% to 91.4%, PPV 90.4% to 92.1%, and NPV 88.9% to 91.3%. Conclusion: [F-18]FDG PET/CECT demonstrated no significant advantage over PET/NCCT for lesion detection, lesion characterization, or diagnostic accuracy in patients with cancer. The use of intravenous contrast material should be limited to select cases to reduce the risk of renal toxicity or anaphylactic reaction, and to minimize unnecessary costs. Keywords: Contrast-enhanced PET/CT, Non-contrast-enhanced PET/CT, Lesion detection, Lesion characterization, Diagnostic accuracy, Cancer, [F-18]FDG

Spectrum of CT Findings in Thoracic Extranodal Non-Hodgkin Lymphoma.

Non-Hodgkin lymphoma (NHL) frequently manifests in extranodal structures in the chest, often in the form of secondary involvement but occasionally as primary disease. Because staging and treatment are affected by the presence of extranodal disease at imaging, radiologists' interpretation and management of suspicious findings are critical to patient care. Unfortunately, owing to considerable imaging overlap with other diseases, primary extranodal lymphoma is difficult to diagnose with imaging alone. Radiologists should have a heightened degree of suspicion in patients at risk (including patients with immune compromise, autoimmune diseases, or a history of stem cell or solid organ transplant) or with particular imaging appearances (including the vertebral wraparound sign, nonresolving consolidation, an infiltrative soft-tissue mass, and lesions demonstrating vascular encasement without invasion). For patients with known NHL, positron emission tomography/computed tomography (PET/CT) using fluorine 18 (18F)-labeled fluorodeoxyglucose (FDG) is now preferred for routine staging in most cases. CT remains heavily used, and identification of subtle extranodal involvement with CT can be improved with use of intravenous contrast material and careful review of multiplanar images. Pericardial effusion, pleural soft tissue (even when mild), mass-like consolidation, perilymphatic nodularity, and new lytic bone lesions are particularly suggestive of secondary involvement in a patient with known NHL. Magnetic resonance imaging is a helpful problem-solving tool when equivocal findings would change staging and treatment. This comprehensive review illustrates the spectrum of CT manifestations of extranodal NHL in the chest, including the pleura, lung, airways, heart, pericardium, esophagus, chest wall, and breast. ©RSNA, 2017.

Diffusion-weighted MR Imaging of the Gastrointestinal Tract: Technique, Indications, and Imaging Findings

Diffusion-weighted magnetic resonance (MR) imaging has emerged as an important tool in the diagnostic work-up of patients with bowel cancer and inflammatory conditions of the gastrointestinal tract. It functions on the basis of the microscopic motion of water molecules in a cellular environment and provides functional information about the water in body tissues. Diffusion-weighted imaging serves to complement conventional MR imaging, and its use may improve the accuracy of tumor detection and staging. It does not rely on the use of intravenous contrast material and may be performed in patients with renal impairment. Because it provides quantitative information about tissue cellularity, diffusion-weighted imaging may be used to distinguish between tissues with altered cellularity (eg, tumors and metastases) and normal tissues. Data from diffusion-weighted MR images enable the calculation of apparent diffusion coefficient (ADC) values, which provide useful information about response to treatment. Malignant gastrointestinal tract tumors have low ADC values, which increase after successful therapy. Diffusion-weighted imaging also plays a role in the evaluation of patients with inflammatory bowel disease and may help assess inflammation and complications, such as abscesses and fistulas. Quantitative measurements of signal intensity at diffusion-weighted imaging may help differentiate actively inflamed bowel from normal bowel, and ADC values provide useful information about disease activity and response to treatment.

Is the Use of Intravenous Contrast Material Truly Safe in Patients with Impaired Renal Function?

HomeRadiologyVol. 251, No. 2 PreviousNext CommunicationsLetters to the EditorIs the Use of Intravenous Contrast Material Truly Safe in Patients with Impaired Renal Function?Mervyn D. CohenMervyn D. CohenAuthor AffiliationsDepartment of Radiology, Indiana University School of Medicine, University Hospital 0663, 550 N University Blvd, Indianapolis, IN 46202-5253 e-mail: [email protected]Mervyn D. CohenPublished Online:May 1 2009https://doi.org/10.1148/radiol.2511081609MoreSectionsFull textPDF ToolsImage ViewerAdd to favoritesCiteTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinked In REFERENCE1 Nguyen SA, Suranyi P, Ravenel JG, et al. Iso-osmolality versus low-osmolality iodinated contrast medium at intravenous contrast-enhanced CT: effect on kidney function. Radiology 2008; 248(1): 97–105. Link, Google ScholarArticle HistoryPublished in print: 2009 FiguresReferencesRelatedDetailsCited ByLa radiologia medica, Vol. 116, No. 1Pharmacoepidemiology and Drug Safety, Vol. 18, No. 11Recommended Articles A Breakthrough in Gadolinum-based Contrast Agent Hypersensitivity ReactionsRadiology2020Volume: 296Issue: 2pp. 322-323Why We Need to Sleep: Glymphatic Pathway and Neurodegenerative DiseaseRadiology2021Volume: 300Issue: 3pp. 669-670Microwave Ablation versus Surgical Resection for Solitary T1N0M0 Papillary Thyroid CarcinomaRadiology2022Volume: 304Issue: 3pp. 704-713Creating a Radiology Quality and Safety Program: Principles and PitfallsRadioGraphics2018Volume: 38Issue: 6pp. 1786-1798Hepatosteatosis and Atherosclerotic Disease: Disentangling the OverlapRadiology: Cardiothoracic Imaging2022Volume: 4Issue: 2See More RSNA Education Exhibits Feeling the Burn: Occupational Burnout in Interventional RadiologyDigital Posters2020Permanent Hysteroscopic Sterilization Device (Essure®) Removal: A Radiologist´s GuideDigital Posters2020Education in the Radiology Reading Room: More than See One, Do One, Teach OneDigital Posters2018 RSNA Case Collection Rhabdomyolisis RSNA Case Collection2022Hepatic AdenomatosisRSNA Case Collection2021Renal Transplant Vein Thrombosis RSNA Case Collection2020 Vol. 251, No. 2 Metrics Altmetric Score PDF download

Early Hepatocellular Carcinoma: Pathology, Imaging, and Therapy

In 1987, Japanese researchers proposed to define the pathological concept of early hepatocellular carcinoma (HCC). However, there are some conceptual differences between the East and the West in the diagnosis and treatment of early HCC. To provide up-to-date data for making a worldwide consensus, this article has collected six papers focused on the management of early HCC, which were presented in the Fifth International Meeting of "Hepatocellular Carcinoma: Eastern and Western Experiences" in Houston in January 2007. In the pathological perspective, the common criteria to discriminate early HCC from dysplastic nodule included hepatocytic invasion of portal triads and septa (stromal invasion). The current imaging modalities such as contrast-enhanced ultrasound (CEUS), computed tomography (CT), and magnetic resonance imaging (MRI) with the use of intravenous contrast material with multiphasic imaging could enhance their ability to accurately characterize early HCC. From the treatment perspective, a single early HCC had a high chance for cure by resection, ablation, or transplantation, which proved to be the earliest clinical entity (Stage 0 HCC). Early HCC is characterized by its incipient malignant nature and by an extremely favorable clinical outcome, thereby justifying its definition.

The Brain in Children: Is Contrast Enhancement Really Needed after Obtaining Normal Unenhanced CT Results?

To retrospectively determine and compare the sensitivity and specificity of unenhanced and contrast material-enhanced computed tomography (CT) (reference standard) in the diagnosis of brain abnormalities and to evaluate any change in diagnosis that resulted from the contrast-enhanced study. This study was approved by the local research ethics board; the requirement for informed consent was waived. The authors reviewed the unenhanced and contrast-enhanced CT scans of the brain obtained in 353 children for indications other than trauma. There were 196 boys and 157 girls aged 0 months to 17.8 years. Scans were read independently by two pediatric neuroradiologists who were blinded to clinical information. The diagnosis for each scan was recorded according to the anatomic section (supratentorial, infratentorial, ventricles, and skull). The final diagnosis was classified as normal, abnormal, or equivocal. kappa Statistics, with 95% confidence intervals, were reported, and the sensitivity, specificity, positive predictive value, and negative predictive value were calculated. Interreader agreement for different anatomic regions varied between good (kappa coefficient, 0.63) and very good (kappa coefficient, 0.88) for unenhanced and contrast-enhanced scans. Sensitivity, specificity, positive predictive value, and negative predictive value for unenhanced scans were 97%, 89%, 87%, and 97%, respectively. The use of contrast material led to a change in the original normal or equivocal diagnosis to an abnormal diagnosis for only five (2.7%) of the 183 normal unenhanced scans. Unenhanced CT of developing brains has high sensitivity and specificity in the diagnosis of pathologic findings. The use of intravenous contrast material after unenhanced CT of the brain in children did not change the diagnosis frequently.

Sequential Changes after Radiofrequency Ablation and Cryoablation of Renal Neoplasms: Role of CT and MR Imaging

Radiofrequency (RF) ablation and cryoablation are increasingly being used as minimally invasive treatments for renal malignancies. Accurate assessment of ablated tumors at postprocedural imaging is essential for evaluating the adequacy of treatment and guiding further management. Renal tumors treated with RF ablation or cryoablation appear as low-attenuation regions at computed tomography (CT) and, relative to renal parenchyma, are generally hypointense at T2-weighted magnetic resonance (MR) imaging and iso- to hyperintense at T1-weighted imaging. The use of intravenous contrast material is essential for the evaluation of possible residual or recurrent tumor. At follow-up CT or MR imaging, successfully treated renal tumors appear as focal masses that demonstrate no evidence of contrast enhancement and that frequently decrease in size over time, whereas residual or recurrent tumor can be detected as abnormal foci of contrast enhancement. Follow-up surveillance imaging is warranted because long-term results for renal tumor ablation are not known, and evaluation for residual, recurrent, or metachronous tumor is essential.

Adrenal Lesions: Attenuation Measurement Differences between CT Scanners

To retrospectively compare unenhanced computed tomographic scans of the same adrenal lesion obtained with two different manufacturers' multidetector scanners to assess whether there are differences in attenuation measurements. The study was approved by the local ethical committee, which waived patient consent, and was conducted in compliance with HIPAA. Electronic searching revealed patients with adrenal nodules scanned with both a Siemens 16-detector row scanner and one of eight GE Medical Systems multi-detector row scanners between January 2000 and September 2004 without the use of intravenous contrast material. Lesions were characterized by using histologic findings, fat content, or size stability. Size stability for 6 months was required unless both scans were obtained within 21 days of each other. Two radiologists independently measured lesion attenuation for regression analysis. Lesions considered benign (< or = 10 HU) on one scan and indeterminate (> 10 HU) on the other were separately analyzed, and technical parameters of scanning were compared. There were 47 patients (27 men, 20 women; age range, 40-86 years; mean age, 64 years) with four metastases, 42 adenomas, and one myelolipoma (long-axis length, 10-85 mm; mean, 24 mm). GE scans were obtained with four-detector row scanners (n = 32), an eight-detector row scanner (n = 2), and 16-detector row scanners (n = 13). Correlation between the two readers was 0.99 for both Siemens and GE scan attenuation measurements. The slope of regression lines for both readers plotting GE attenuation (y-axis) against Siemens attenuation (x-axis) was less than 1, which indicated a slight but statistically significant tendency for GE scans to have lower attenuations than do Siemens scans. For both readers, there were more lesions indeterminate (> 10 HU) on Siemens scans but benign (< or = 10 HU) on GE scans than the reverse (McNemar test, P < .02 for reader 1, not significant for reader 2). Average Siemens and GE scan technical parameters were similar. There are only slight differences in attenuation of adrenal nodules measured on scans obtained with different scanners.

Evaluation of cardiac tumors with magnetic resonance imaging

Primary cardiac neoplasms are rare, and are more commonly benign than malignant. However, metastases are by far the most common cardiac neoplasms. MRI allows evaluation of myocardial infiltration, pericardial involvement and/or extracardiac extension. MRI overcomes the usual limitations of echocardiography and assesses more accurately changes in cardiac function. Specific tumoral characterization is only possible in cases of myxoma, lipoma, fibroma and hemangioma. Suggestive features of malignancy are right side location, extracardiac extension, inhomogeneity in signal intensity of the tumor and pericardial effusion. The use of intravenous contrast material improves tumor characterization and depiction of tumor borders. MRI also allows differentiation of tumor from other nontumoral masses such as intracavitary tumors or fibromuscular elements of the posterior wall of the right atrium.

Magnetic resonance imaging of hepatocellular carcinoma

Hepatocellular carcinoma (HCC), the most common primary hepatic malignancy, usually develops in patients with cirrhosis, growing sequentially from low-grade dysplastic nodules to frank malignant HCC. Its recognition is critical because curative treatment and prognosis require early diagnosis. Survival in patients with HCC relates directly to the number, size, and extent of lesions at diagnosis. Imaging of HCC is complicated because the tumor has a varied imaging appearance and frequently coexists with other cirrhotic nodules. Magnetic resonance imaging (MRI), the best available diagnostic technique, offers good contrast resolution and diagnostic sensitivity ranging from 33% to 77%. The main difficulty is not in diagnosing large tumors, but rather small tumors (<2 cm), because of considerable overlap on imaging between benign (regenerative), borderline (dysplastic), and malignant nodules. Increasing degrees of histological malignancy are associated with increasing arterialization and loss of portal blood supply; therefore, recognition of HCC requires dynamic imaging with gadolinium-enhanced T1-weighted sequence. Typically, HCC is a focal lesion with high signal intensity on T2-weighted images, variable signal intensity on T1-weighted images, intense arterial phase enhancement after gadolinium injection, and isointensity or hypointensity at the portal venous phase. The sensitivity of MRI for detecting small lesions is low, and improvement is still needed. Newer contrast agents, higher field strength (3 Tesla) imaging, and perfusion and diffusion MRI techniques possibly will provide greater sensitivity and specificity for detecting small HCCs in the future.

CT attenuation of colorectal polypoid lesions: evaluation of contrast enhancement in CT colonography.

The aim of this study was to calculate pre- and postcontrast CT attenuation values of benign colorectal polyp and carcinoma lesions detected by virtual colonoscopy, and to investigate whether contrast enhancement of these lesions can be potentially used for differentiation from residual fluid in the colon. Fifteen benign polyps and 21 colorectal carcinoma lesions detected by virtual colonoscopy in 18 patients were included in our study. All of the polyps and carcinoma lesions were confirmed by colonoscopic biopsy. Measurement of CT attenuation values was performed in precontrast (supine) and postcontrast (prone) scans for each polyp and carcinoma. The CT attenuation values of residual fluid in the colon was also measured from the same location before and after intravenous contrast administration. On unenhanced CT scan mean attenuation values of benign polyps and colorectal carcinomas were 32.4 and 42.6 HU, respectively. Following contrast enhancement, mean attenuation value increased to 78.9 HU for polyps and 90.7 HU for carcinomas. Increase in the CT attenuation values of these lesions was significant ( p<0.0001). Mean CT attenuation value of residual fluid before and after administration of IV contrast were 14.6 and 13.8 HU, respectively. The difference between CT attenuation value of residual fluid in the colon before and after contrast material was not significant ( p=0.29). Colorectal benign polyps and carcinomas demonstrate significant enhancement following contrast administration and use of intravenous contrast material during virtual colonoscopy may help in some cases in differentiating these solid lesions from residual colonic fluid that does not enhance.

Contrast optimization and scan timing for single and multidetector-row computed tomography.

Various complex pharmacokinetic interrelationships affect the use of contrast media for computed tomography (CT) imaging. These include factors related to each patient's unique body habitus and their degree of health, such as their age, gender, height, weight, and cardiovascular status. Of equal importance are factors related to the contrast material injection. The volume, concentration, and rate of injection all affect the degree of enhancement that is achieved with an injection of contrast material. In addition, the injection technique--whether the contrast is infused at a constant injection rate (uniphasic injection) or whether the rate is altered during the injection (multiphasic injection)--also affects the magnitude and duration of contrast enhancement. In body CT imaging, the liver poses unique challenges in managing the use of intravenous contrast material because of its dual blood supply and the need to complete imaging before equilibrium occurs between the intravascular and extravascular compartments. The magnitude of hepatic enhancement that is ultimately achieved is related primarily to the amount of iodinated contrast material that accumulates in the extravascular space within the target organ, independent of the speed of the CT scanner. The key determinant of the onset of the equilibrium phase is the injection duration. Given that a high injection flow rate (4-5 ml/s) is desirable for arterial phase imaging, the injection duration is maintained by using an appropriate contrast volume. Thus, modifications of the total iodine dose are best performed by altering the contrast concentration. Use of a high contrast concentration (400 mg iodine/ml) may be advantageous in heavy patients, or in patients in whom routine imaging is married with a need for high-detail imaging of the vasculature with high resolution CT angiography. The magnitude of arterial enhancement that is achieved is related to both the concentration of contrast and the rate of administration. The speed of the scanner determines its ability to record image data during the most advantageous time period, the peak of arterial enhancement. Thus, rapid imaging is particularly advantageous for optimal contrast use in CT angiography as well as in multiphasic imaging of the parenchymal organs.

Use of high concentration contrast media (HCCM): principles and rationale—body CT

Numerous complex pharmacokinetic interrelationships affect the use of contrast media for computed tomography (CT) imaging. The volume, concentration, and rate of injection, all affect the degree of enhancement that is achieved with an injection of contrast material. In addition, the injection technique, whether the contrast is infused with a constant injection rate (uniphasic injection) or whether the rate is altered during the injection (multiphasic injection) also affect the magnitude and duration of contrast enhancement. In body CT imaging, the liver poses unique challenges in managing the use of intravenous contrast material because of its dual blood supply and the need to complete imaging before equilibrium occurs between the intravascular and extravascular compartments. The magnitude of hepatic enhancement that is ultimately achieved is related primarily to the amount of iodinated contrast material that accumulates in the extravascular space within the target organ, independent of the speed of the CT scanner. The key determinant of the onset of the equilibrium phase is the injection duration. Given that a high injection flow rate (4–5 ml/s) is desirable for arterial phase imaging, the injection duration is maintained with use of an appropriate contrast volume. Thus, modifications of total iodine dose are best done with alterations in contrast concentration. The magnitude of arterial enhancement that is achieved is related to both the concentration and rate of contrast administration. The speed of the scanner determines its ability to record image data during the most advantageous time period, the peak of arterial enhancement. Thus, rapid imaging is particularly advantageous for optimal contrast use in CT angiography as well as in multiphasic imaging of the parenchymal organs.

Whole-body computed tomography screening.

Publisher Summary This chapter gives an introduction to whole-body computed tomography (CT) screening (WBS). Dr. Harvey Eisenberg began performing WBS with an electron beam CT scanner, using a technique involving a 20-sec scanning acquisition from the neck to the pelvis to include coronary calcium scoring, lung cancer screening, bone densitometry, and an abdominal survey. WBS includes a scan of the head, neck, chest, abdomen, and pelvis. However, WBS is practiced variably in conjunction with other targeted screening examinations such as a chest, abdomen, and pelvis. A serious concern among critics of WBS is that no standards exist for equipment, techniques, personnel, interpretation, or quality for untargeted scans of the whole body. Most practitioners appear to avoid the use of intravenous contrast material because it adds risk, requires monitoring, and add substantial time and cost. However, others observe that many findings are considerably more difficult to detect or characterize without contrast material and that there is limited value to noncontrast examinations for the abdomen. Overdiagnoses represent histologically malignant lesions or other potentially serious diseases that do not progress rapidly enough to harm the patient. Such overdiagnoses, false-positive tests, and incidental findings are the primary flaws of screening because they cause anxiety, procedures, and costs that do not lead to medical benefit. However, among these categories, perhaps incidental findings have received the least attention. Incidental findings may be defined as those that are not related to symptoms or previously detected abnormal physical findings or laboratory results. They are often benign lesions that lead to no symptoms, morbidity, or mortality if ignored.

Use of radiologic techniques to screen for hepatocellular carcinoma.

The role of imaging in screening and evaluation of cirrhotic patients is to assess the extent of cirrhosis and portal hypertension (liver morphology, varices, ascites, vessel patency) and to detect hepatocellular carcinoma (HCC). Ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI) have valuable roles, with catheter angiography usually reserved for specific problem solving. Ultrasonography is highly operator-dependent, and detection of focal masses is often difficult or impossible because of large patient body habitus and hepatic steatosis and fibrosis, which attenuate the ultrasound beam. For sonography, as well as CT and MRI, the use of intravenous contrast material with multiphasic imaging (arterial, portal venous, and delayed) is essential to accurately depict the morphology and hemodynamics of focal hepatic lesions. Computed tomography and MRI are highly accurate in diagnosis of large HCC but are much less accurate for lesions less than 2 cm in diameter. Many factors influence the choice and timing of imaging tests, including the etiology of the chronic liver disease, the elevation of serum tumor markers, and the availability and excellence of equipment and personnel. In our practice, helical multiphasic CT is obtained at least every 12 months, more frequently in patients judged to be at high risk for HCC.