Xenon contrast enhancement in computed body tomography.

Xenon has been investigated as a contrast medium for conventional radiography, and in vitro as a contrast medium for computed tomography. The authors evaluated xenon contrast enhancement in vivo for CT body scanning. Nine healthy subjects had CT scans before and during xenon inhalation. Concentrations of xenon used varied from 10--50%. Consistent useful changes in attenuation from inhaled xenon were found in the lung but not in abdominal organs. Lung attenuation varied linearly with the xenon concentration in the inhaled gas. Inhalation of xenon concentrations greater than 30% resulted in side effects. Further studies are required to demonstrate whether xenon contrast enhancement is of diagnostic value in computed tomography.     

Extravascular iodine in contrast enhancement with computed tomography

Summary Using specimens obtained at operation, tissue-blood ratios of iodinated contrast material (iodine), and in some cases also those of red blood cell tracer (⁵¹Cr), were measured in 23 patients with various kinds of intracranial mass lesions. Results provided confirmatory evidence on the major role played by extravascular iodine in the positive enhancement effect with computed tomography.     

Effects of computed tomography contrast medium factors on contrast enhancement

The various nonionic iodinated contrast media used in contrast computed tomography (CT) studies differ in terms of their composition, characteristics, and iodine concentration (mgI/ml), as well as the volume injected (ml). Compared with ionic iodinated contrast media, nonionic iodinated contrast media are low-osmolar agents, with different agents having different osmotic pressures. Using a custom-made phantom incorporating a semipermeable membrane, the osmotic flow rate (HU/s) could easily be measured based on the observed increase in CT numbers, and the relationship between the osmotic pressure and the osmotic flow rate could be obtained (r(2)=0.84). In addition, taking the effects of patient size into consideration, the levels of contrast enhancement in the abdominal aorta (AA) and inferior vena cava (IVC) were compared among four types of CT contrast medium. The results showed differences in contrast enhancement in the IVC during the equilibrium phase depending on the type of contrast medium used. It was found that the factors responsible for the differences observed in enhancement in the IVC were the osmotic flow rate and the volume of the blood flow pathways in the circulatory system. It is therefore considered that the reproducibility of contrast enhancement is likely to be reduced in the examination of parenchymal organs, in which scanning must be performed during the equilibrium phase, even if the amount of iodine injected per unit body weight (mgI/kg) is maintained at a specified level.     

A protocol for the use of contrast enhancement in cranial computed tomography

There is some confusion regarding the indications for and methodology of the use of contrast material in cranial computed tomography. Some authors recommend a nonenhanced scan in all cases, followed by an enhanced scan if indicated by the symptoms or the appearance of the unenhanced scan. Others have questioned the value of the nonenhanced scan in patients with tumor. The authors offer a protocol for the use of contrast material. Possible tumor patients are scanned with contrast material alone; other patients are scanned either (a) without contrast material or (b) both with and without contrast material, depending upon the most likely clinical diagnosis.     

Pituitary computed tomography: is contrast enhancement necessary?

Direct coronal computed tomography of the pituitary fossa, before and after enhancement with intravenous contrast medium, was performed on 25 consecutive patients with hyperprolactinaemia. The images were viewed separately by two independent observers and the pituitary height, width and contour, and the visibility of the infundibulum, optic chiasm and hypothalamus were assessed. The presence and size of any possible pituitary tumour was recorded. The administration of intravenous contrast medium made no significant difference to the pituitary measurements, the visibility of the infundibulum of hypothalamus, or the detection of possible pituitary tumours. There was an inconsistent improvement in the visibility of the optic chiasm following enhancement. The arguments against an unenhanced examination are discussed and refuted. It is proposed that routine administration of intravenous contrast medium is unnecessary when investigating moderate hyperprolactinaemia.     

Low dose arterial contrast enhancement for cranial computed tomography in renal insufficiency

In patients with severe renal insufficiency, the high iodine doses used for intravenous contrast medium enhanced CT can lead to renal injury. To minimize renal toxicity in one such patient, dynamic contrast enhanced CT was performed during right common carotid arterial infusion of 17 ml of 30% diatrizoate meglumine solution. Intense homogeneous contrast enhancement of an otherwise isodense mass permitted a diagnosis of meningioma, with excellent definition of tumor extent.     

Opacification of ascitic fluid on delayed contrast computed tomography scans

Ascitic fluid opacification on delayed intravenous contrast computed tomography scans was observed in eight consecutive patients imaged. This apparently common phenomenon may alter both the sensitivity and the specificity of ascitic fluid detection. It may also serve as a diagnostic aid by making nonascitic intra-abdominal fluid collections (ie, pseudocyst and cystic tumor) more apparent.     

Choice of contrast material for four-hour delayed contrast-enhanced computed tomography of the liver

Four-hour delayed contrast-enhanced computed tomography (DCECT) shows promise for improved detection of focal liver lesions. No previous studies have examined the use of nonionic contrast materials for DCECT. The authors undertook a case-controlled study in monkeys to define the relative efficacies of iopamidol and diatrizoate for DCECT. In this model, diatrizoate made the liver significantly more opaque at four hours than did iopamidol (mean 126.5 vs 87.6 HU, P less than or equal to 0.05). Opacification of the gallbladder and biliary tract occurred more often and was denser with diatrizoate. The relative efficacies of biliary excretion correlate with similarities in molecular structure. While it has been shown that the increased density from DCECT with diatrizoate may allow detection of more metastatic lesions, the clinical utility of the inferior parenchymal density obtained with iopamidol, extrapolated to be approximately 11 to 14 HU in humans, remains to be-established.     

Low tube voltage improves computed tomography imaging of delayed myocardial contrast enhancement in an experimental acute myocardial infarction model

OBJECTIVE: We sought to evaluate the influence of tube voltage on the visualization of acute myocardial infarction (MI) in cardiac multislice spiral computed tomography (MSCT). MATERIALS AND METHODS: Acute MI was induced in 12 domestic pigs by a 45-minute balloon occlusion of the left anterior descending artery. Delayed enhancement magnetic resonance imaging was performed 15 minutes after the injection of 0.2 mmol/kg Gd-DTPA. On the same day, retrospectively ECG-gated MSCT was performed at 120, 100, and 80 kV (16x0.75mm, 550mAseff.) 15 minutes after the injection of 140 mL of iopromide (1 g/iodine/kg). The pigs were killed and the hearts were excised and stained with 2,3,5-triphenyltetrazolium chloride. The area of acute MI, contrast-to-noise ratio (CNR), and percent signal difference were compared among the different imaging techniques by applying Bland-Altman plots and 2-way analysis of variance. RESULTS: On MSCT at 120, 100, and 80 kV, the respective mean acute MI sizes were 18.4+/-11.4%, 19.3+/-11.5%, and 20.5+/-11.6%. The mean MI sizes were 20.8+/-12.2% and 20.1+/-12.4% on magnetic resonance imaging and 2,3,5-triphenyltetrazolium chloride staining. Analysis of variance did not show any statistically significant differences between the different techniques with respect to the size of acute MI (P=0.9880). Comparing the different kV settings on MSCT, the highest percent signal difference (74.7+/-12.1%) and the highest CNR (6.7+/-1.8) between infarcted and healthy remote myocardium were achieved at 80 kV. CONCLUSIONS: When compared with routine scan protocols, low tube voltage MSCT allows for the assessment of the MI size with an improved CNR and contrast resolution. This technique appears to be advantageous for assessing myocardial viability from contrast enhanced late-phase MSCT.     

Computed tomography of intracranial chondroma with emphasis on delayed contrast enhancement

Intracranial chondroma is an unusual cartilaginous tumor originating from the base of the skull. We report on two cases of intracranial chondroma that showed delayed contrast enhancement on CT after high-dose administration of contrast medium. This CT feature may be useful to differentiate chondromas from other tumors of the skull base such as meningiomas and neurinomas.     

Time-course characterization of the computed tomography contrast enhancement of an iodinated blood-pool contrast agent in mice using a volumetric flat-panel equipped computed tomography scanner

OBJECTIVE: The objective of this study was to determine the time-course of computed tomography (CT) contrast enhancement of an iodinated blood-pool contrast agent. METHODS: Five C57BL/6 mice were anesthetized, imaged at baseline, and given an iodinated blood-pool contrast agent. Micro-CT scans were acquired at 0, 0.25, 0.5, 1, 2, 4, 8, and 24 hours after injection. The mean CT number was determined in a region of interest in 7 organs. RESULTS: The CT contrast enhancement was plotted as a function of time for each organ. We identified an imaging window immediately after injection suitable for visualizing the vascular system and a second imaging window at 24 hours for visualizing liver and spleen. CONCLUSIONS: A single injection of the blood-pool contrast agent can be used for dual-phase investigations of the vasculature (t = 0 hours) and liver (t = 24 hours), which can be applied to studies of liver tumors or disease.     

Patterns of contrast enhancement of tuberculous lymph nodes demonstrated by computed tomography.

The purpose of this study was to evaluate the contrast-enhanced CT characteristics of pathologic thoraco-abdominal lymph nodes in 38 patients infected with Mycobacterium tuberculosis (30 without AIDS and eight with AIDS). Unenhanced scans of chest, abdomen and pelvis were also done in all cases. The CT attenuation values and the enhancement characteristics of the largest node or group of lymph nodes were evaluated in a dynamic sequence over a period of 10 min. On unenhanced CT the nodes were of low attenuation (less than 30 HU) in 18 cases and of soft tissue attenuation (greater than 35 HU) in 20 cases. Four post-contrast patterns of enhancement were found: (i) peripheral rim enhancement (n = 22); (ii) inhomogeneous enhancement (n = 8); (iii) homogeneous enhancement (n = 6); and (iv) homogeneous nonenhancing nodes (n = 2). Increase of attenuation and obliteration of perinodal fat was found in 13 cases, most of them with the peripheral rim enhancement pattern. Seven cases had a combination of enhancing patterns in the same nodal group. The central enhancement was usually moderate (mean, 30 HU) but was marked (greater than 60 HU) in three patients with the homogeneous enhancement pattern. Neither the nodal attenuation values nor the patterns of enhancement are characteristic of tuberculosis, however adenopathy showing peripheral rim-enhancement with relative low attenuation centres can suggest a diagnosis of tuberculosis in the appropriate clinical setting.     

Patterns of brain perfusion: dynamic computed tomography using intravenous contrast enhancement.

A representation of cerebral perfusion is obtained using cranial computed tomography following the rapid bolus injection of iodinated intravenous contrast medium. This technique permits the definition of four gross patterns of perfusion (normal, circulatory arrest, hypoperfusion, and hyperperfusion). This classification is affirmed in an experimental model of cerebral infarction in the baboon. The limitations of dynamic imaging using computed tomography are reviewed.