Helical (spiral) CT of the abdomen

Half-value layer measurements using solid-state detectors and single-rotation technique with lead apertures in spiral computed tomography with and without a tin filter

Solid-state detectors (SSDs) may be used along with a lead collimator for half-value layer (HVL) measurement using computed tomography (CT) with or without a tin filter. We aimed to compare HVL measurements obtained using three SSDs (AGMS-DM+ , X2 R/F sensor, and Black Piranha) with those obtained using the single-rotation technique with lead apertures (SRTLA). HVL measurements were performed using spiral CT at tube voltages of 70-140 kV without a tin filter and 100-140 kV (Sn 100-140 kV) with a tin filter in increments of 10 kV. For SRTLA, a 0.6-cc ionization chamber was suspended at the isocenter to measure the free-in-air kerma rate (K ˙ air ) values. Five apertures were made on the gantry cover using lead sheets, and four aluminum plates were placed on these apertures. HVLs in SRTLA were obtained fromK ˙ air decline curves. Subsequently, SSDs inserted into the lead collimator were placed on the gantry cover and used to measure HVLs. Maximum HVL differences of AGMS-DM+ , X2 R/F sensor, and Black Piranha with respect to SRTLA without/with a tin filter were - 0.09/0.6 (only two Sn 100-110 kV) mm, - 0.50/ - 0.6 mm, and - 0.17/(no data available) mm, respectively. These values were within the specification limit. SSDs inserted into the lead collimator could be used to measure HVL using spiral CT without a tin filter. HVLs could be measured with a tin filter using only the X2 R/F sensor, and further improvement of its calibration accuracy with respect to other SSDs is warranted.

Clinical Feasibility of Zero TE Skull MRI in Patients with Head Trauma in Comparison with CT: A Single-Center Study

BACKGROUND AND PURPOSE

Conventional MR imaging techniques cannot produce optimal images of bone structures because bone has little water and a very short T2 life span. The aim of this study was to investigate the clinical feasibility of skull MR imaging using the zero TE sequence in patients with head trauma by assessing its diagnostic image quality and quantitative measurement compared with CT images.

MATERIALS AND METHODS

Thirteen enrolled patients with head trauma were assessed using brain CT and skull MR imaging. Image quality was graded on a 5-point Likert scale to compare the 2 modalities. To evaluate quantitative analyses between the 2 imaging modalities, we measured skull thickness and normalized bone tissue signal. Interobserver reliability was assessed using weighted κ statistics and the intraclass correlation coefficient.

RESULTS

Both imaging techniques clearly depicted skull fractures in all 13 patients. The mean scores for skull MR imaging and CT were 4.65 ± 0.56 and 4.73 ± 0.45 (P = .157), respectively, with substantial interobserver agreement (P < .05). The 2 imaging modalities showed no difference in skull thickness (P = .092) and had good correlation (r ² = 0.997). The mean value of normalized bone tissue signal among the 3 layers of the skull was relatively consistent (P = .401) with high interobserver agreement (P < .001).

CONCLUSIONS

Zero TE skull MR imaging has diagnostic image quality comparable with that of CT images. It also provides consistent results on the quantitative measurement of cortical bone with CT images.

Emergence of "Big Data" and Its Potential and Current Limitations in Medical Imaging

Although electronic imaging was performed in the early 1950s in nuclear medicine, it was the introduction of computed tomography in 1972 that caused a revolution in medical imaging in that it marked the beginning of the inevitable transformation to digital imaging. This transformation is now more or less complete. While initially these CT images were relatively small, comprised of only about 6400 pixels per slice, the steady move toward higher spatial resolution, multislice imaging, digital radiography, and fluoroscopy rapidly increased the size of images and the amount of data required to be stored, processed, displayed, and moved about in a medical imaging department. The more recent introduction of digital pathology with submicron-sized pixels and the need for color further increases these demands. Rising work volumes in hospital, a push for cost containment, and a move toward greater precision in diagnosis and treatment of disease all work together to motivate the development of automated image analysis algorithms and techniques to improve efficiencies in in vivo imaging and pathology. This may require bringing together information from different imaging and nonimaging sources within the institution. While technological development has provided practical means for storage of the burgeoning data load and the use of multiple processors and high-speed networks has enabled more sophisticated analysis locally or in the cloud, challenges remain in terms of the ability to integrate data from different systems, the development of appropriately annotated image bases for training and testing of algorithms, and issues around privacy and ownership in obtaining access to patient-related data.

Evaluation of lung tumor response to therapy: Current and emerging techniques

Lung tumor response to therapy may be evaluated in most instances by morphological criteria such as RECIST 1.1 on computed tomography (CT) or magnetic resonance imaging (MRI). However, those criteria are limited because they are based on tumoral dimensional changes and do not take into account other morphologic criteria such as density evaluation, functional or metabolic changes that may occur following conventional or targeted chemotherapy. New techniques such as dual-energy CT, PET-CT, MRI including diffusion-weighted MRI has to be considered into the new technical armamentarium for tumor response evaluation. Integration of all informations provided by the different imaging modalities has to be integrated and represents probably the future goal of tumor response evaluation. The aim of the present paper is to review the current and emerging imaging criteria used to evaluate the response of therapy in the field of lung cancer.

Intra-individual diagnostic image quality and organ-specific-radiation dose comparison between spiral cCT with iterative image reconstruction and z-axis automated tube current modulation and sequential cCT

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Superiority of spiral versus sequential cCT in image quality and organ-specific-radiation dose.

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Spiral cCT: lower organ-specific-radiation-dose in eye lense compared to tilted sequential cCT.

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State-of-the-art IR spiral cCT techniques has significant advantages over sequential cCT techniques.

Objectives

To prospectively evaluate image quality and organ-specific-radiation dose of spiral cranial CT (cCT) combined with automated tube current modulation (ATCM) and iterative image reconstruction (IR) in comparison to sequential tilted cCT reconstructed with filtered back projection (FBP) without ATCM.

Methods

31 patients with a previous performed tilted non-contrast enhanced sequential cCT aquisition on a 4-slice CT system with only FBP reconstruction and no ATCM were prospectively enrolled in this study for a clinical indicated cCT scan. All spiral cCT examinations were performed on a 3rd generation dual-source CT system using ATCM in z-axis direction. Images were reconstructed using both, FBP and IR (level 1–5). A Monte-Carlo-simulation-based analysis was used to compare organ-specific-radiation dose. Subjective image quality for various anatomic structures was evaluated using a 4-point Likert-scale and objective image quality was evaluated by comparing signal-to-noise ratios (SNR).

Results

Spiral cCT led to a significantly lower (p < 0.05) organ-specific-radiation dose in all targets including eye lense. Subjective image quality of spiral cCT datasets with an IR reconstruction level 5 was rated significantly higher compared to the sequential cCT acquisitions (p < 0.0001). Consecutive mean SNR was significantly higher in all spiral datasets (FBP, IR 1–5) when compared to sequential cCT with a mean SNR improvement of 44.77% (p < 0.0001).

Conclusions

Spiral cCT combined with ATCM and IR allows for significant-radiation dose reduction including a reduce eye lens organ-dose when compared to a tilted sequential cCT while improving subjective and objective image quality.

A study on the usefulness of methylcellulose in rectal CT based on the analysis of the differences in absorption of radiation-permeable and radiation-impermeable materials

PURPOSE

The purpose of this study was to use various radiation-permeable and radiation-impermeable materials, used to facilitate the observation of a lesion during a rectal computed tomography (CT) scan, in order to determine the best material to use.

MATERIALS AND METHODS

In regard to the study method, the radiation-permeable and radiation-impermeable materials of physiological saline, methylcellulose, contrast medium, ultrasound gel, and air were used to perform scanning with scan parameters that were used in general abdominal scanning. The GSI mode was used for material analysis.

RESULTS

According to the results of the phantom study, the average CT value was 25.5 ± 5.9 HU for physiological saline, 77.6 ± 7.3 HU for methylcellulose, 3,070 ± 0.1 HU for contrast medium, 74.1 ± 11.9 HU for ultrasound gel, and -954.1 ± 10.3 HU for air. According to the analysis of materials by energy, contrast medium and physiological saline showed a dramatic decrease in the CT value as energy increased. Methylcellulose showed a gradual decrease in CT value, whereas air showed a small change in CT value according to the graph.

CONCLUSIONS

Out of these materials, methylcellulose had the advantage of reducing discomfort in patients, and was more convenient for examiners before and after the rectal CT scan.

Measurement of table feed speed in modern CT

The purpose of this study was to develop and evaluate a noninvasive method to assess table feed speed (mm/s) in modern commercial computed tomography (CT) systems. The table feed (mm/rotation) was measured at selected nominal table feed speeds, given as low (26.67 mm/s), intermediate (48.00 mm/s), and high (64.00 mm/s), by utilizing a computed radiography (CR) cassette installed with a photostimulable phosphor plate. The cassette was placed on the examination table to travel through the isocenter longitudinally, with a total scan length of over 430 mm. The distance travelled was employed to determine the total table feed length. To calculate the table feed speed, gantry rotation time was measured concurrently at a preselected nominal rotation time of 750 ms. Upon completion of data acquisition, the table feed and gantry rotation time were analyzed and used to calculate the actual table feed speed (mm/s). Under the low table feed speed setting, the table feed speed was found to be 26.67 mm/s. Similarly, under the intermediate and high table feed speed settings, the table feed speed was found to be 48.10 and 64.07 mm/s, respectively. Measurements of the table feed speed can be accomplished with a CR system and solid-state detector, and the table feed speed results were in excellent agreement with the nominal preset values.

Measurement of gantry rotation time in modern ct

The purpose of this study was to develop and evaluate a noninvasive method to assess rotation time in modern commercial computed tomography (CT) systems. The rotation time was measured at a selected nominal rotation time (400 ms) utilizing two types of solid‐state detectors: the RTI's CT Dose Profiler (CTDP) and Unfors’ Xi (Xi) probes. Either CTDP or Xi was positioned on the inner cover of the gantry and a sheet of lead (1 mm thick) placed on top of the detector. Since a pair of two successive peaks is used to determine the gantry rotation time, by necessity the helical scan must be employed. Upon completion of the data acquisition, these peak times were determined with the dedicated software to obtain rotation time. The average rotation time obtained with CTDP and Xi operated under the dedicated software was found to be 400.6 and 400.5 ms, respectively. The detector for this measurement need not be specifically designed for CT dosimetry. The measurements of CT scanner rotation time can be accomplished with a radiation probe designed for the CT application or a conventional radiation probe designed for radiography and fluoroscopy applications. It is also noteworthy to point out that the measurement results are in good agreement between the two radiation detector systems. Finally, clinical medical physicists should be aware of the accuracy and precision of gantry rotation time, and take into consideration for QA where and when applicable.

PACS number: 87.57.Q‐

Evaluating an Evolutionary Particle Swarm Optimization for Fast Fuzzy C-Means Clustering on Liver CT Images

An Evolutionary Particle Swarm Optimization based on the Fractional Order Darwinian method for optimizing a Fast Fuzzy C-Means algorithm is proposed. This chapter aims at enhancing the performance of Fast Fuzzy C-Means, both in terms of the overall solution and speed. To that end, the concept of fractional calculus is used to control the convergence rate of particles, wherein each one of them represents a set of cluster centers. The proposed solution, denoted as FODPSO-FFCM, is applied on liver CT images, and compared with Fast Fuzzy C-Means and PSOFFCM, using Jaccard Index and Dice Coefficient. The computational efficiency is achieved by using the histogram of the image intensities during the clustering process instead of the raw image data. The experimental results based on the Analysis of Variance (ANOVA) technique and multiple pair-wise comparison show that the proposed algorithm is fast, accurate, and less time consuming.

CT volume measurement for prognostic evaluation of unresectable hepatocellular carcinoma after TACE

AIM: To analyze the value of computed tomography (CT) volume measurements for evaluation of the survival rate of unresectable hepatocellular carcinoma (HCC) patients after transcatheter arterial chemoembolization (TACE).

METHODS: One hundred and sixty-six unresectable HCC patients after TACE were involved in this retrospective study. Hepatic CT scan was performed for all patients before and 4 wk to 2 mo after TACE to define the morphologic features of HCC including its largest diameter, volume, product of the greatest axial dimension, tumor to liver volume ratio (TTLVR), and tumor shrinkage ratio. Clinical variables used in the study included gender, age, pattern of tumor growth, number of lesions, Child-Pugh classification of liver function, repeated TACE times, pre- or post-treatment α-fetoprotein (AFP) level, portal vein cancerous thrombus, tumor metastasis, degree of lipiodol retention within the tumor, and percutaneous ethanol injection. The correlation between survival time and clinical variables of patients or lesions was analyzed by combining morphologic features with the corresponding clinical and general data as input. A Cox proportional hazard model was used to analyze prognostic factors. The Kaplan-Meier method was used to calculate the cumulative survival time. Influence of the parameters on prognosis was analyzed by the log-rank test.

RESULTS: The overall 6, 12, 24, 36 and 60 mo cumulative survival rates were 78.92%, 49.85%, 23.82%, 15.60% and 8.92%, respectively. The median survival time was 12 mo. Univariate and multivariate analysis showed that only 4 parameters were the independent prognostic factors including TTLVR (χ² = 14.328, P < 0.001), portal vein cancerous thrombus (χ² = 5.643, P = 0.018), repeated TACE times (χ² = 8.746, P = 0.003), and post-treatment serum AFP level (χ² = 5.416, P = 0.020). When the TTLVR value was less than 70%, the survival time was inversely correlated with the TTLVR value.

CONCLUSION: CT volume measurement technique can predict the prognosis of unresectable HCC patients after TACE.

Current concepts and advances: computerized tomography in sports medicine

Computed tomography (CT) is a widely used imaging technique. With the introduction of multidetector row technology, CT has been further refined. Although the focus of this transformation has been body and cardiac imaging, orthopedic imaging has benefited greatly. Specifically, the improvements in CT have made it possible to obtain submillimeter-thick slices that enable the creation of high-resolution multiplanar reformations from a single scan. These images usually are indistinguishable from direct plane acquisitions and provide unparalleled detail. Additionally, the factors responsible for causing CT image artifacts when hardware is present are much better understood and the improvements in CT technique and technology can be exploited to provide better images of patients with orthopedic hardware. The detailed multiplanar visualization of joints facilitates CT arthrography that has undergone a renaissance. CT arthrography is useful in the very large athlete or patient, the claustrophobic, and for those patients who fail a conventional magnetic resonance examination or magnetic resonance arthrogram.

Prospective, blinded comparison of helical CT and CT arterial portography in the assessment of hepatic metastasis from colorectal carcinoma

OBJECTIVE

This prospective blinded comparison of helical CT and helical CT arterial portography aimed to detect liver metastasis from colorectal carcinoma.

METHODS AND MATERIALS

50 patients with colorectal carcinoma were evaluated comparing helical CT with helical CT arterial portography. Each imaging study was evaluated on a 5-point ROC scale by radiologists blinded to the other imaging findings, and the results were compared, with the surgical and pathologic findings as the gold standard.

RESULTS

Of the 127 lesions found at pathology identified as metastatic colorectal cancer, helical CT correctly identified 85 (69%) and CT portography 96 (76%). When subgroups with lesions <3 cm (48 patients) and patients with maximum tumor size <3 cm (18 patients) were considered, CT portography was always better than helical CT in terms of sensitivity, specificity, positive predictive value, and negative predictive value. ROC analysis adjusting for multiple lesions per patient revealed significantly greater area under the curve (AUC) for the subgroup of lesions <3 cm (CT-AUC of 77% and CT portography AUC of 81%; P = 0.002).

CONCLUSIONS

For identification of large metastases, helical CT and CT portography have similar yield. However, for detection of small liver metastases, CT portography remains superior for lesion detectability.

Imaging of acute pyelonephritis in the adult

The diagnosis of acute pyelonephritis in adults is predominantly made by a combination of typical clinical features of flank pain, high temperature and dysuria combined with urinalysis findings of bacteruria and pyuria. Imaging is generally reserved for patients who have atypical presenting features or in those who fail to respond to conventional therapy. In addition, early imaging may be useful in diabetics or immunocompromised patients. In such patients, imaging may not only aid in making the diagnosis of acute pyelonephritis, but more importantly, it may help identify complications such as abscess formation. In this pictorial review, we discuss the role of modern imaging in acute pyelonephritis and its complications. We discuss the growing role of cross-sectional imaging with computed tomography (CT) and novel magnetic resonance imaging (MRI) techniques that may be used to demonstrate both typical as well as unusual manifestations of acute pyelonephritis and its complications. In addition, conditions such as emphysematous and fungal pyelonephritis are discussed.

Efficacy of multislice computed tomography for gastroenteric and hepatic surgeries

AIM: To determine the efficacy of multislice CT for gastroenteric and hepatic surgery.

METHODS: Dual-phase helical computed tomography was performed in 50 of 51 patients who underwent gastroenteric and hepatic surgeries. Twenty-eight, eighteen and four patients suffering from colorectal cancer, gastric cancer, and liver cancer respectively underwent colorectal surgery (laparoscopic surgery: 6 cases), gastrectomy, and hepatectomy. Three-dimensional computed tomography imaging of the inferior mesenteric artery, celiac artery and hepatic artery was performed. And in the follow-up examination of postoperative patients, multiplanar reconstruction image was made in case of need.

RESULTS: Scans in 50 patients were technically satisfactory and included in the analysis. Depiction of major visceral arteries, which were important for surgery and other treatments, could be done in all patients. Preoperative visualization of the left colic artery and sigmoidal arteries, the celiac artery and its branches, and hepatic artery was very useful to lymph node dissection, the planning of a reservoir and hepatectomy. And multiplanar reconstruction image was helpful to diagnosis for the postoperative follow-up of patients.

CONCLUSION: Three-dimensional volume rendering or multiplanar reconstruction imaging performed by multislice computed tomography was very useful for gastroenteric and hepatic surgeries.

Assessment of image quality of a standard and three dose-reducing protocols in adult cranial CT

The purpose of this study was to analyze the effect of various tube current settings (mAs) and optimize the image quality and dose for adult cranial CT protocol. Sixty adult patients who underwent a cranial CT scanning for different indications were subdivided into three subgroups. Subjective image and noise quality scores and quantitative noise measurements were selectively studied on three reference levels (cerebellar, basal ganglia and centrum semiovale levels). For each subgroup, only one level was studied. Head circumference (HC) and the maximum anteroposterior diameter (MAPD) of each patient were measured. At 50% decreased dose protocol, there was no poor quality score at any level. At nearly 60% decreased dose protocol, the incidence of poor quality scores was much higher at the cerebellar level than at the other two levels. For the same protocol number, quantitative noise measurements were higher at the cerebellar level than the other two supratentorial levels. The correlation was found to be significant between HC, MAPD and quantitative noise measurements, and there was a non-significant correlation between HC and subjective noise scores. In adult cranial CT, depending on the level, a dose reduction of up to 60% may be possible while maintaining image quality.

Recent advances in CT imaging of liver metastases

Multidetector computed tomography provides robust evaluation of the hepatic parenchyma. It plays a critical role in the detection of liver metastases and the assessment of treatment response to therapy. In this article, we discuss the role of multidetector computed tomography in the detection and characterization of hepatic metastases, and the value of image processing with volume rendering and maximum-intensity projection techniques in the accurate delineation of hepatic vascular anatomy and the segmental localization of lesions. This information is critical in the diagnosis and treatment of patients with metastatic disease and is essential in surgical and nonsurgical planning.

CT doses in children: a multicentre study

We evaluated examination protocols used for common CT procedures of paediatric patients at different hospitals in Belgium in order to determine whether adjustments related to patient size are made in scanning parameters, and to compare patient doses with proposed reference levels. Three paediatric hospitals and one non-paediatric hospital participated in the study. Weighted CT dose-index (CTDI(w)), dose-length product (DLP) and effective dose (E) were evaluated for three patient ages (1 year, 5 years and 10 years) and three common procedures (brain, thorax and abdomen). CTDI(w) and DLP values higher than the reference levels were found for all types of evaluated examination. E ranged from 0.4 mSv to 2.3 mSv, 1.1 mSv to 6.6 mSv, and 2.3 mSv to 19.9 mSv for brain, thorax and abdomen examinations, respectively. All centres but one adapted their protocols as a function of patient size. However, no common trend in the selection of protocols was observed. Some centres divided the whole range of patient size into only two/three groups by age, while others classified the patients into six groups by weight. It was also observed that some centres used the same mAs for the total range of patient sizes and decreased the pitch factor for small children, which resulted in higher doses. This indicates the importance of careful selection of technical scan parameters. If CT parameters used for paediatric patients are not adjusted on the basis of examination type, age and/or size of the child, then some patients will be exposed to an unnecessarily high radiation dose during CT examinations.

The Relationship of Abdominal Fat Mass Assessed by Helical or Conventional Computed Tomography to Serum Leptin Concentration

In the present study, we focused on the relationship of intra-abdominal visceral fat (VF) or subcutaneous fat (SF) mass to serum leptin levels, and also on the relationship of leptin to serum lipid and lipoprotein concentration. Subjects with obesity (26 men, 26 women) were recruited for this study. We obtained helical CT scans with a tube current of 150 mA, voltage of 120 kV and 2:1 pitch (table speed in relation to slice thickness), starting at the upper edge of the liver and continuing to the pelvis. The intra-abdominal visceral fat (VF) volume was measured by drawing a line within the muscle wall surrounding the abdominal cavity. The abdominal SF volume was calculated by subtracting the VF volume from the total abdominal fat volume. By comparison, the abdominal VF and SF areas were determined at the umbilical level by the established slice-by-slice CT scanning technique. We found: 1) abdominal SF mass, either as volume or area, was a more important determinant of serum leptin than was VF mass; 2) among TC, TG, HDL-C and LDL-C, only TG had a positive correlation to serum leptin levels in men, whereas in women no lipid parameters had any relationship with leptin; and 3) VF mass had a positive correlation to serum TC and TG in men, whereas SF did not. The present study provides considerable evidence on the relationship between abdominal fat mass and serum leptin, and shows that the relationships between serum leptin and serum lipids and lipoproteins are not straightforward. We also suggest that fat area measured by conventional CT is a better indicator than its corresponding volume assessed by helical CT, based on the present results showing its closer association to serum lipids.

Imaging diagnosis of pancreato-biliary diseases: A control study

AIM: To evaluate the clinical value of various imageological methods in diagnosing the pancreato-biliary diseases and to seek the optimal procedure.

METHODS: Eighty-two cases of pancreato-biliary diseases confirmed by surgery and pathology were analyzed. There were 38 cases of cholelithiasis, 34 cases of pancreato-biliary tumors and 10 other cases. The imageological methods included B-US, CT, ERCP, PTC, cross-sectional MRI and MR cholangiopancreatography (MRCP).

RESULTS: The accuracy rate of MRCP in detecting the location of pancreato-biliary obstruction was 100%. In differentiating malignant from benign obstruction, the sensitivity of the combination of MRCP and cross-sectional MRI was 82.3%, the specificity was 93.8%, and the accuracy rate was 89.0%. The accuracy rate for determining the nature of obstruction was 87.8%, which was superior to that of B-US (P = 0.0000) and CT (P = 0.0330), but there was no significant difference between direct cholangiopancreatography and the combination of MRCP and conventional MRI (P = 0.6666).

CONCLUSION: In most cases, MRCP can substitute direct cholangiopancreatography for diagnosis. The combination of MRCP and cross-sectional MRI should be considered as an important means in diagnosing the pancreato-biliary diseases, pre-operative assessment and post-operative follow-ups.

The efficacy of helical CT in the diagnosis of small bowel obstruction

OBJECTIVE

To evaluate the usefulness and reliability of helical computed tomography (CT) for patients with small bowel obstruction.

METHODS AND MATERIAL

Helical CT findings of 41 patients were evaluated prospectively on the basis of the presence and the cause of obstruction, and the presence of strangulation.

RESULTS

In the determination of the cause of the obstruction sensitivity and specificity of CT were 84 and 90%, respectively. Of the 19 patients undergoing surgery, 6 had strangulation and were correctly identified by CT.

CONCLUSION

Helical CT is an accurate method in the detection of small bowel obstruction, especially for evaluating the cause and vascular complications of obstruction.

Very-high-flow injection rate for upper abdominal CT angiography

BACKGROUND

The purpose of this study was to compare a very-high-flow injection-rate method (group A) and a conventional injection-rate method (group B) for visualization of upper abdominal arteries by multidetector helical computed tomography (MDHCT).

METHODS

The subjects were 240 patients suspected to have abdominal lesions. They were randomly assigned to group A (120 patients) and group B (120 patients). In group A, the bilateral medial cubital veins were punctured, and contrast medium was infused at a rate of 8.6-9.6 ml/s. In group B, the unilateral medial cubital vein was punctured, and contrast medium was infused at a rate of 2.0-3.0 ml/s. The quality of vascular visualization was graded as poor, good, or excellent by three radiologists.

RESULTS

All visualizations of the celiac trunk (CE) and superior mesenteric artery (SMA) were graded as excellent in both group A and group B. Visualization grades of the subsegmental branches of the hepatic artery (HA), right gastric artery (RGA), cystic artery, dorsal pancreatic artery (DPA), and superior pancreaticoduodenal artery (SPDA) were good or excellent, in 75% (paging method)/53.3% (three-dimensional method), 85%/30%, 77.7%/18.3%, 76.7%/28.3%, and 88.3%/42.5%, respectively, in group A, and 33.3%/11.7%, 46.7%/3.4%, 41.6%/5%, 55%/4.2%, and 72.5%/14.2%, respectively, in group B. The appearance rate of intrahepatic portal branches was 28.3% in group A and 66.7% in group B in the arterial dominant phase.

CONCLUSION

Group A showed better visualization results than Group B in upper abdominal arteries according to MDHCT.

CT tumor measurement for therapeutic response assessment: comparison of unidimensional, bidimensional, and volumetric techniques initial observations

PURPOSE

To compare unidimensional, bidimensional, and volumetric techniques for evaluation of treatment response in patients with liver metastases from breast cancer in a phase III clinical trial.

MATERIALS AND METHODS

Helical computed tomographic (CT) studies in 38 patients with liver metastases from breast cancer who were enrolled in a phase III clinical trial were evaluated before treatment and at 6 months after treatment. Two subspecialty radiologists measured all lesions on transverse CT scans with use of electronic calipers according to both unidimensional and bidimensional criteria. Volumetric measurements were made by tracing individual lesions. Measurements of individual lesions were summed to obtain patient response, which was categorized as complete response, disappearance of lesions; partial response, greater than 30% decrease in tumor diameter (unidimensional), greater than 50% reduction in tumor area (bidimensional), or greater than 65% reduction in tumor volume (volumetric); disease progression, greater than 20% increase in tumor diameter, greater than 25% increase in tumor area, or greater than 73% increase in tumor volume: or stable disease (size response other than that of complete response, partial response, or disease progression).

RESULTS

In 37 patients, there was concordant treatment response with use of unidimensional and bidimensional techniques. Volumetric measurement produced results different from those of the unidimensional and bidimensional techniques in 12 and 13 patients, respectively. In six patients with partial response per unidimensional and bidimensional criteria, the response based on the volumetric technique was stable disease. In two patients with stable disease per bidimensional and unidimensional criteria, the response was partial response by volumetric measurement. In four patients with disease progression per bidimensional and unidimensional criteria, the response was stable disease per volumetric criteria.

CONCLUSION

Volumetric measurement of tumor burden gives different results for treatment response compared with that of the unidimensional or bidimensional technique in a considerable proportion of patients.

Use of early-phase dynamic spiral computed tomography for the primary screening of multiple trauma

The effectiveness of early-phase dynamic spiral computed tomography (CT) of the whole body for screening multiple trauma was compared with that of conventional incremental CT. Thirty-six patients with suspected blunt hemorrhagic injuries were prospectively assigned to undergo either standard uniphasic incremental CT or spiral CT enhanced during the early arterial phase. In comparison with incremental CT, the wider scan coverage in spiral CT resulted in the detection of more injuries. Spiral CT showed an excellent enhancement of both the arteries and parenchyma with a reduced volume of contrast material, however, more contrast artifacts were observed. All extravasations detected in spiral CT were from the arteries and required subsequent interventions including transcatheter embolization. Primary screening with early-phase dynamic spiral CT for hemorrhagic multiple trauma was found to be useful for determining the applications of subsequent angiographic intervention as well as evaluating lesions caused by injury.

Small hypervascular hepatocellular carcinoma revealed by double arterial phase CT performed with single breath-hold scanning and automatic bolus tracking

OBJECTIVE

The purpose of this study was to evaluate the usefulness of double arterial phase CT for the detection of small hypervascular hepatocellular carcinomas, using an automated bolus-tracking technique to initiate the hepatic arterial phase CT.

MATERIALS AND METHODS

Double arterial and late phase contrast-enhanced helical CT scans were obtained on 287 consecutive patients suspected of having hepatocellular carcinoma. These included 56 patients with 90 small (< or 3 cm) hepatocellular carcinomas and 50 patients with no hepatocellular carcinomas. CT scans of these patients were interpreted by three reviewers. The first arterial phase scan was initiated automatically 10 sec after the bolus-tracking program detected the threshold enhancement of 50 H in the abdominal aorta. Three reviewers interpreted the late phase CT scans in combination with the first, second, or both hepatic arterial phases. Measures of the reviewers' detection of hepatocellular carcinoma included analysis of interobserver variation, sensitivity, specificity, and area under receiver operating characteristic curve (A(z)).

RESULTS

The time elapsed from bolus initiation to threshold aortic enhancement ranged from 10 to 24 sec (mean, 13 sec), resulting in initiation of the first arterial phase CT scan from 20 to 34 sec (mean, 23 sec). The combination of late phase CT and both first and second arterial phase images showed significantly better performance than the combination of the late phase and either the first or second arterial phases, although the difference was most evident in comparison with the combination of second arterial and late phases.

CONCLUSION

An automated bolus-tracking program can be used to optimize the timing of hepatic arterial phase CT. Multiphasic CT performed using this technique is useful in detection of small hepatocellular carcinoma.

A novel method of measuring intra-abdominal fat volume using helical computed tomography

OBJECTIVES

:We present a novel method of scanning for intra-abdominal fat volume by helical computed tomography (CT), and describe the clinical significance of measuring the volumes of intra-abdominal visceral fat (V(vol)) and subcutaneous fat (S(vol)) vs these respective areas determined by conventional slice-by-slice CT at the umbilical level.

METHOD

Subjects with obesity or hyperlipidemia (79 men, 74 women) were recruited for this study. We obtained helical CT scans with a tube current of 150 mA, voltage of 120 kV and 2:1 pitch (table speed in relation to slice thickness), starting at the upper edge of the liver and continuing until the pelvis. The intra-abdominal visceral fat volume was measured by drawing a line within the muscle wall surrounding the abdominal cavity. The abdominal subcutaneous fat volume was calculated by subtracting the visceral fat volume from the total abdominal fat volume. By comparison, the intra-abdominal visceral and subcutaneous fat areas were determined at the umbilical level by the established slice-by-slice CT scanning technique.

RESULTS

V(vol) was correlated positively with visceral fat area (V(area)) measured by conventional CT in both genders (in men (n=79) V(vol) vs V(area), r=0.81 P<0.0001; in women (n=74) V(vol) vs V(area), r=0.85, P<0.0001). S(vol) also showed a positive correlation with subcutaneous fat area (S(area)) in both genders (in men (n=78) S(vol) vs S(area), r=0.95, P<0.0001; in women (n=74) S(vol) vs S(area), r=0.92, P<0.0001).

CONCLUSION

We have reported a novel method for measuring intra-abdominal fat volume by the use of helical CT.

Current techniques of computed tomography. Helical CT, multidetector CT, and 3D reconstruction

The many recent advances in CT technology have secured its position as the modality of choice in routine liver imaging and have improved its performance in several problem-solving applications. In addition, improvements in postprocessing software (e.g., in speed, efficiency, and automated algorithms) have increased their use in clinical practice. Multiplanar reformations, 3D renderings, and high-quality CT angiographic displays have become extremely valuable both in image interpretation and in communicating information to surgeons and referring physicians.

A practical approach to the first iteration in the optimization of radiation dose and image quality in CT: estimates of the collective dose savings achieved

CT is a diagnostic imaging modality giving higher patient dose in comparison with other radiological procedures. It contributed an estimated 20% to the collective effective dose to the UK population from medical X-rays in 1990, rising to an estimated 40% in 1999. Tremendous national effort has been expended in reducing patient doses from other radiological procedures with considerable success, but much of the collective dose reduction achieved has been offset by a corresponding increase in the collective dose from CT. Over a period of about 2 years, following the installation of a helical CT scanner, CT scan parameters in this hospital have been adjusted with the aim of working towards optimization of image quality and patient dose. A 33% reduction in annual collective effective dose has been achieved, from about 16.5 manSv to 11 manSv. However, despite this dose reduction, the annual collective effective dose to our sub-population is 2.8 times the value 9 years ago. The increase is almost entirely the result of an increased application of CT; 6149 examinations per annum in 1999 compared with 2210 in 1991. The crucial importance of reducing patient doses from this modality is discussed. Indicative effective doses and image noise values are presented for examination protocols approaching optimization.

Binding rate constant of Tc-99m DTPA galactosyl human serum albumin measured by quantitative dynamic SPECT--clinical evaluation as a total and regional liver function test

To evaluate the clinical utility of a new method with dynamic single photon emission computed tomography (SPECT) and scatter and attenuation compensation to estimate both total and regional liver function quantitatively. Five controls, 20 patients with chronic liver disease, and 2 patients with Budd-Chiari syndrome were studied. Dynamic liver SPECT data were acquired during 20 minutes after injection of Technetium (Tc)-99m diethylenetriaminepentaacetic acid (DTPA) galactosyl human serum albumin (GSA) with scatter and attenuation compensation. The binding rate constant of Tc-99m GSA (Ku) was derived quantitatively from the Patlak plot based on kinetic models for GSA receptor binding. The mean Ku was obtained by dividing the Ku value (total Ku) by the liver volume. Both total and mean Ku were significantly lower in patients with chronic liver disease than in controls (302 +/- 112 vs. 523 +/- 78 ml/min; p < 0.001, 0.26 +/- 0.11 vs. 0.43 +/- 0.03 ml/min/cm3; p < 0.001). In the patient group, both total and mean Ku were significantly correlated with the results of conventional liver function tests and the histological severity of chronic liver disease. In 2 patients with Budd-Chiari syndrome, the mean Ku was lower in the right lobe, where the hepatic veins were occluded, than in the left lobe, where draining veins were patent. In conclusion, this method is a reliable diagnostic technique for estimating total and regional liver function.

Surveillance of pre-malignant disease of the pancreatico-biliary system

Technical advancements in ultrasonography, contrast-enhanced computed tomography and magnetic resonance imaging, as well as the wider availability of these ultramodern imaging techniques, have resulted in the early detection and a better classification of various asymptomatic and symptomatic pancreatico-biliary lesions. Pre-malignant biliary and pancreatic lesions are rare disorders, and no clear data are available to define their malignant potential. Because of the lack of controlled epidemiological data, the time span for malignant transformation and its frequency cannot be defined in the majority of these lesions. Adenomyomatosis of the gallbladder and gallbladder polyps larger than 10 mm should be treated by cholecystectomy even in asymptomatic patients because of an increased risk of malignant transformation. Chronic cholangitis, primary sclerosing cholangitis and choledochal cysts are also pre-malignant conditions. The timing of surgery, once it is advised for a pre-malignant condition that is still benign, should, however, be individualized to the particular patient situation. In patients with chronic pancreatitis, surgery may be indicated for disease-related complications. In as much as chronic pancreatitis predisposes to a higher risk of pancreatic cancer, any suspicion of malignancy should warrant a surgical exploration. Intraductal papillary tumours and mucin-producing pancreatic tumours are other pre-malignant pancreatic lesions whose malignant potential cannot be precisely determined pre-operatively. They should be resected in situations where there is a high degree of suspicion even without a clear objective diagnosis. In conclusion, pre-malignant hepato-biliary and pancreatic lesions of uncertain pathology should undergo early resection in view of treatment limitations and the dismal prognosis of established cancers. While hepato-biliary and pancreatic surgery is nowadays performed in specialized centres, with a low post-operative morbidity and mortality, it is equally important to understand that observation alone with regular computed tomography or magnetic resonance imaging control can no longer be recommended in the management of these lesions.

Helical CT protocols for the abdomen and pelvis: a survey

OBJECTIVE

We surveyed members of the Society of Computed Body Tomography/Magnetic Resonance to evaluate current techniques used for helical CT in the abdomen and pelvis.

MATERIALS AND METHODS

The survey was distributed to 70 members (36 institutions) of the Society of Computed Body Tomography/Magnetic Resonance. The survey included general questions related to abdominal and pelvic helical CT and also asked the members to write a protocol for 12 hypothetical requisitions.

RESULTS

Thirty-two members (46%) responded, representing 28 institutions (78%). The number of protocols for helical CT of the abdomen and pelvis at each institution ranges from 2 to 35 (median, 11). IV contrast material is administered for 90% (median) of abdominal and pelvic CT examinations. Nonionic contrast material is used for 68% (median) of these examinations. IV contrast material is used by 100% of institutions for tumor staging protocols except for one institution that does not use IV contrast material for lymphoma staging. Fifty percent of the institutions obtain two- or three-phases of liver images for breast cancer staging. For all protocols, the average collimation and reconstruction interval is 7 mm except for renal (5 mm) and adrenal (4 mm) protocols. Rectal contrast material is administered most commonly for colon cancer staging (39% of institutions).

CONCLUSION

There is a wide range in the number of protocols used for helical CT in the abdomen and pelvis among the responding institutions. Most protocols include use of nonionic IV contrast material injected at a rate of 3 ml/sec and a collimation of 7 mm.

Paraanastomotic aneurysms of the abdominal aorta: a 15-year experience review

The aim of the study is a retrospective review of clinical presentation and management of paraanastomotic aneurysms of the abdominal aorta (PAAA) surgically treated in our Department. From January 1984 to December 1998, 2183 aortic prosthetic grafts were implanted. During the same period, 24 patients were treated for PAAA, 19 false and five true aneurysms. Symptoms were present in 10 patients. Surgical management included tube grafting interposition (14), aortobifemoral bypass (2), graft removal with extraanatomic bypass (2) and with in situ revascularization by arterial homograft (4). Nine patients died during operation or in the early postoperative period, six died during follow-up. Mortality in symptomatic patients was 70%, while in asymptomatic group was 14% (P=0.01). Rupture of false PAAA was very frequent (47% of cases). PAAA are infrequent complications of proximal aortic graft revascularization and tend to be asymptomatic until rupture occurs. The incidence of mortality is very different in asymptomatic versus symptomatic group; rupture is particularly frequent in false PAAA, which must soon undergo surgery when diagnosed. Since PAAA may develop at any time after surgery, their incidence increase in relationship with the length of postoperative interval: therefore, all patients submitted to abdominal graft revascularization need a lifetime surveillance program.

Tailored helical CT evaluation of acute abdomen

Helical computed tomography (CT) allows rapid, cost-effective evaluation of patients with acute abdominal pain. Tailoring the examination to the working clinical diagnosis by optimizing constituent factors (eg, timing of acquisition, contrast material used, means and rate of contrast material administration, collimation, pitch) can markedly improve diagnostic accuracy. Rapid (>/=3 mL/sec) intravenous injection of contrast material is required for optimal assessment of acute pancreatitis, ischemic bowel, aortic aneurysm, and aortic dissection. Narrow collimation and small reconstruction intervals can help detect calculi in the biliary system and genitourinary tract. Tailored helical CT in patients with acute pyelonephritis usually involves several acquisitions through the kidneys during various phases of renal enhancement. In patients with suspected renal infarction, CT protocol must include an acquisition during the corticomedullary phase. Helical CT with 5-mm collimation through the lower abdomen and pelvis is used to evaluate patients with suspected diverticulitis. Use of both oral and intravenous contrast material can help localize small bowel perforation and characterize related complications. Tailored helical CT for assessment of abdominal hemorrhage consists of initial unenhanced CT followed by optional contrast material-enhanced CT. Clear communication between the radiologist, the patient, and the referring physician is essential for narrowing the differential diagnosis into a working diagnosis prior to helical CT.

One year's clinical experience with unenhanced spiral computed tomography for the assessment of acute loin pain suggestive of renal colic

OBJECTIVE

To assess the use of unenhanced spiral computed tomography (CT) as the primary investigation of choice for suspected acute renal colic in clinical urological practice. Patients and Methods Between 1 August 1997 and 31 July 1998, all patients attending a hospital accident and emergency department with acute loin pain suggestive of renal colic underwent a physical examination, urine analysis, plain abdominal radiography (if clinically indicated) and unenhanced spiral CT. The effective radiation dose and financial cost of unenhanced spiral CT and standard three-film emergency intravenous urography (IVU) were calculated.

RESULTS

In all, 116 patients were assessed, 63 of whom had calculi and related secondary phenomena of obstruction identified on unenhanced spiral CT. There were two false-positive and one false-negative result. An alternative urinary tract diagnosis was made in four patients, including two with renal cell carcinoma and one ureteric transitional cell carcinoma. Causes other than in the urinary tract were diagnosed in three patients, i.e. two with ovarian cyst and one with sigmoid diverticulitis. The effective radiation dose of unenhanced spiral CT was 4.7 mSv and that for three-film IVU was 1.5 mSv. The costs of both IVU and unenhanced spiral CT were identical.

CONCLUSIONS

Unenhanced spiral CT allows a rapid, contrast-medium-free, anatomically accurate diagnosis of urinary tract calculi and in the present series had a sensitivity of 98% and a specificity of 97%. CT provided an alternative diagnosis in 6% of patients. These advantages must be weighed against the threefold greater radiation dose of unenhanced spiral CT than with three-film IVU, and in practice the requirement for a radiologist to interpret routine axial scans.

Imaging of hepatocellular carcinoma

Recent improvements in the treatment of hepatocellular carcinoma (HCC) have resulted in a need to identify the disease at an early stage. The wide range of imaging techniques available reflects the difficulty in demonstrating small HCC, particularly in the cirrhotic liver. This article reviews the current imaging techniques available for the diagnosis of HCC.

Pancreatic CT imaging: effects of different injection rates and doses of contrast material

PURPOSE

To assess the effects of the intravenous injection rate and dose of contrast material on pancreatic computed tomography (CT).

MATERIALS AND METHODS

A total of 126 patients were divided at random into four groups with different injection rates and doses. Groups 1 and 2 underwent injection of 2 mL per kilogram of body weight of 300 mg of iodine per milliliter of contrast material, and groups 3 and 4 underwent injection of 1.5 mL/kg. The injection rate was 5 mL/sec for groups 1 and 3 and 3 mL/sec for groups 2 and 4. Single-level serial CT scanning was performed at the level of the pancreatic head, and the pancreatic enhancement value was calculated.

RESULTS

The maximum pancreatic enhancement value was 99 HU +/- 18 (mean +/- SD) for group 1, 90 HU +/- 18 for group 2, 86 HU +/- 15 for group 3, and 74 HU +/- 13 for group 4. There were significant differences in the maximum pancreatic enhancement value between groups 1 and 2 (P = .045), between groups 3 and 4 (P = .001), between groups 1 and 3 (P = .016), and between groups 2 and 4 (P = .001).

CONCLUSION

Both a higher dose and a faster injection rate increased the maximum pancreatic enhancement value.

Alveolar architecture of clear cell renal carcinomas (< or = 5.0 cm) show high attenuation on dynamic CT scanning

BACKGROUND

To establish the correlation between tumor appearance on CT and tumor histology in renal cell carcinomas.

METHODS

The density and attenuation patterns of 96 renal cell carcinomas, each < or = 5 cm in greatest diameter, were studied by non-enhanced CT and early and late after bolus injection of contrast medium using dynamic CT. The density and attenuation patterns and pathological maps of each tumor were individually correlated.

RESULTS

High attenuated areas were present in 72 of the 96 tumors on early enhanced dynamic CT scanning. All 72 high attenuated areas were of the clear cell renal cell carcinoma and had alveolar architecture. The remaining 24 tumors that did not demonstrate high attenuated foci on early enhanced scanning included three clear cell, nine granular cell, six papillary, five chromophobe and one collecting duct type. With respect to tumor architecture, all clear cell tumors of alveolar architecture demonstrated high attenuation on early enhanced scanning.

CONCLUSION

Clear cell renal cell carcinomas of alveolar architecture show high attenuation on early enhanced dynamic CT scanning. A larger number of patients are indispensable to obtaining clear results. However, these findings seem to be an important clue to the diagnosis of renal cell carcinomas as having an alveolar structure.

Extrahepatic abdominal imaging in patients with malignancy: comparison of MR imaging and helical CT, with subsequent surgical correlation

PURPOSE

To compare state-of-the-art magnetic resonance (MR) imaging with single-phase helical computed tomography (CT) in abdominal screening for extrahepatic disease in patients with proved malignancy.

MATERIALS AND METHODS

Fifty-seven patients with known malignancy underwent abdominal contrast material-enhanced helical CT and MR imaging from 1994 through 1997. Prospective interpretations of CT scans and MR images were used to assess each modality's sensitivity in depicting malignant extrahepatic tumor at 17 anatomic sites. Imaging findings were compared with surgical results in all patients.

RESULTS

Helical CT depicted 101 (66%) of 154 surgically confirmed extrahepatic tumor sites; MR imaging depicted 139 (90%) (P < .001). MR imaging depicted tumor in more patients at 11 of the 17 anatomic sites; at six sites, MR imaging and helical CT were equivalent. MR imaging showed significantly greater depiction of extrahepatic tumor for the peritoneum (P < .05), bowel (P < .01), and mesentery (P < .05). False-negative interpretations would have altered patient care had the extrahepatic tumor remained undetected in 13 patients for helical CT and in six patients for MR imaging.

CONCLUSION

State-of-the-art MR imaging can be used for effective abdominal screening for extrahepatic tumor in patients with malignancy. Compared with single-phase helical CT, MR imaging depicted more sites of extrahepatic tumor and was particularly advantageous for the peritoneum, mesentery, and bowel.

Helical computed tomography of renal lesions

Helical computed tomography is a new technique that acquires a volumetric data set of both kidneys within a single breath-hold. It has proved to be superior to conventional computed tomography. Multiphasic helical computed tomography after the administration of contrast material shows advantages concerning the detection and characterization of renal lesions and the preoperative staging of renal cell carcinomas. The proper scan protocol for a sufficient examination of the kidneys is described as well as its diagnostic value. The characteristic computed tomography morphology of benign and malignant renal lesions is reviewed and the advantages of helical computed tomography are illustrated.

Heterogeneous splenic enhancement patterns on spiral CT images in children: minimizing misinterpretation

PURPOSE

To (a) determine the appearances and timing of heterogeneous splenic enhancement at spiral computed tomography (CT) and (b) identify variables influencing heterogeneous splenic enhancement.

MATERIALS AND METHODS

Sequential isolevel (24-mAs) CT images of the spleen obtained at 6-second intervals after initiation of contrast material injection in 112 children (mean age, 4.5 years) were reviewed. Heterogeneity characteristics assessed included type, onset, maximum, and resolution. Relationship to variables (injection rate, age, splenomegaly) was assessed with the Fisher exact test.

RESULTS

Eighty-one of the 112 patients (72%) had transient heterogeneity: archiform (45 patients), diffuse (25 patients), and focal (11 patients). Mean times were as follows: initial visualization after onset of contrast material injection, 19.2 seconds; maximum heterogeneity, 27.3 seconds; and resolution, 47.4 seconds. Statistically significant relationships were seen between frequency of heterogeneity and injection rate (> or = 1 mL/sec, 82%; < 1 mL/sec, 50% [P = .001]), age (> 1 year, 76%; < or = 1 year, 46% [P = .04]), and splenomegaly (present, 20%; absent, 77% [P = .048]).

CONCLUSION

Heterogeneous splenic contrast enhancement is common, has several patterns of appearance, and is predictably encountered during the 70 seconds after the initiation of contrast material injection. Injection rate, age, and presence of splenic disease influence the frequency with which these artifacts are encountered.

Arterial dynamic appearance of common bile duct carcinoma by helical CT on angiography (angio-HCT): four operated cases

We present four cases of common bile duct carcinoma in which both angiographic helical CT (angio-HCT) and pancreatoduodenectomy were done in the 3 years since 1995. Angio-HCT was performed with direct infusion of the contrast medium through the gastroduodenal artery inserted on angiography. Angio-HCT displayed the tumors as lower density areas in contrast to the strong enhancement of the circumferential nontumorous areas, including the pancreas and duodenum.

Management of hepatic metastases

Although the liver is the most common site of metastatic disease from a variety of tumor types, isolated hepatic metastases most commonly occur from colorectal cancer and, less frequently, from neuroendocrine tumors, gastrointestinal sarcoma, ocular melanoma, and others. Complete evaluation of the extent of metastatic disease, both intrahepatically and extrahepatically, is important before considering treatment options. Based on a preponderance of uncontrolled studies for hepatic metastatic colorectal carcinoma, surgical resection offers the only potential for cure of selected patients with completely resected disease, with 5-year survival rates of 25% to 46%. Systemic and hepatic arterial infusion chemotherapy may be useful treatment options in patients with unresectable disease and possibly as an adjuvant treatment after liver resection. Other techniques of local tumor ablation, including cryotherapy and radiofrequency ablation, although promising, remain unproved. Management of hepatic metastases from neuroendocrine tumors and other noncolorectal primary tumors should be individualized based on the patient's clinical course, extent of disease, and symptoms.