CT evaluation of suspected hepatic metastases: comparison of techniques for i.v. contrast enhancement

Rapid Quality Assessment of Nonrigid Image Registration Based on Supervised Learning

When preprocedural images are overlaid on intraprocedural images, interventional procedures benefit in that more structures are revealed in intraprocedural imaging. However, image artifacts, respiratory motion, and challenging scenarios could limit the accuracy of multimodality image registration necessary before image overlay. Ensuring the accuracy of registration during interventional procedures is therefore critically important. The goal of this study was to develop a novel framework that has the ability to assess the quality (i.e., accuracy) of nonrigid multimodality image registration accurately in near real time. We constructed a solution using registration quality metrics that can be computed rapidly and combined to form a single binary assessment of image registration quality as either successful or poor. Based on expert-generated quality metrics as ground truth, we used a supervised learning method to train and test this system on existing clinical data. Using the trained quality classifier, the proposed framework identified successful image registration cases with an accuracy of 81.5%. The current implementation produced the classification result in 5.5 s, fast enough for typical interventional radiology procedures. Using supervised learning, we have shown that the described framework could enable a clinician to obtain confirmation or caution of registration results during clinical procedures.

Comparison of Abdominal Computed Tomographic Enhancement and Organ Lesion Depiction Between Weight-Based Scanner Software Contrast Dosing and a Fixed-Dose Protocol in a Tertiary Care Oncologic Center

OBJECTIVE

This study aimed to evaluate the quality of enhancement and solid-organ lesion depiction using weight-based intravenous (IV) contrast dosing calculated by injector software versus fixed IV contrast dose in oncologic abdominal computed tomographic (CT) examinations.

METHODS

This institutional review board-exempt retrospective cohort study included 134 patients who underwent single-phase abdominal CT before and after implementation of weight-based IV contrast injector software. Patient weight, height, body mass index, and body surface area were determined. Two radiologists qualitatively assessed examinations (4 indicating markedly superior to -4 indicating markedly inferior), and Hounsfield unit measurements were performed.

RESULTS

Enhancement (estimated mean, -0.05; 95% confidence interval [CI], -0.19 to 0.09; P = 0.46) and lesion depiction (estimated mean, -0.01; 95% CI, -0.10 to 0.07; P = 0.79) scores did not differ between CT examinations using weight-based IV contrast versus fixed IV contrast dosing when a minimum of 38.5 g of iodine was used. However, the scores using weight-based IV contrast dosing were lower when the injector software calculated and delivered less than 38.5 g of iodine (estimated mean, -0.81; 95% CI, -1.06 to -0.56; P < 0.0001). There were no significant differences in measured Hounsfield units between the CT examinations using weight-based IV contrast dosing versus fixed IV contrast dosing.

CONCLUSIONS

Oncologic CT image quality was maintained or improved with weight-based IV contrast dosing using injector software when using a minimum amount of 38.5 g of iodine.

Comparison of Non-Enhanced, Bolus Enhanced, and Delayed Scanning Techniques in Computed Tomography of Hepatic Tumours

Non-enhanced, bolus contrast medium enhanced and 4 to 6 hours delayed computed tomography of the liver was performed in a prospective study of 53 patients. Forty patients had focal lesions, in 12 of these they were hypervascular. Contrast medium was administered as an initial bolus followed by a rapid injection of meglumine metrizoate (Isopaque Cerebral). The total iodine dose varied between 56 and 63 g, which gave an average increase in attenuation of 14 HU in normal parenchyma comparing delayed with non-enhanced scanning. Presence and extent of focal lesions were evaluated in a randomized and independent analysis by two radiologists. The percentage of examinations with correct tumour description was higher with bolus scanning (observer I 73%, observer II 75%) and delayed scanning (observer I 75%, observer II 78%) than with non-enhanced scanning (observers I and II 67%). An optimal bolus technique requires an exact timing of the contrast medium administration and scanning. Delayed scanning provides an excellent supplement when the bolus examination is suboptimal or shows equivocal findings.

Graphics Processing Unit-Accelerated Nonrigid Registration of MR Images to CT Images During CT-Guided Percutaneous Liver Tumor Ablations

RATIONALE AND OBJECTIVES

Accuracy and speed are essential for the intraprocedural nonrigid magnetic resonance (MR) to computed tomography (CT) image registration in the assessment of tumor margins during CT-guided liver tumor ablations. Although both accuracy and speed can be improved by limiting the registration to a region of interest (ROI), manual contouring of the ROI prolongs the registration process substantially. To achieve accurate and fast registration without the use of an ROI, we combined a nonrigid registration technique on the basis of volume subdivision with hardware acceleration using a graphics processing unit (GPU). We compared the registration accuracy and processing time of GPU-accelerated volume subdivision-based nonrigid registration technique to the conventional nonrigid B-spline registration technique.

MATERIALS AND METHODS

Fourteen image data sets of preprocedural MR and intraprocedural CT images for percutaneous CT-guided liver tumor ablations were obtained. Each set of images was registered using the GPU-accelerated volume subdivision technique and the B-spline technique. Manual contouring of ROI was used only for the B-spline technique. Registration accuracies (Dice similarity coefficient [DSC] and 95% Hausdorff distance [HD]) and total processing time including contouring of ROIs and computation were compared using a paired Student t test.

RESULTS

Accuracies of the GPU-accelerated registrations and B-spline registrations, respectively, were 88.3 ± 3.7% versus 89.3 ± 4.9% (P = .41) for DSC and 13.1 ± 5.2 versus 11.4 ± 6.3 mm (P = .15) for HD. Total processing time of the GPU-accelerated registration and B-spline registration techniques was 88 ± 14 versus 557 ± 116 seconds (P < .000000002), respectively; there was no significant difference in computation time despite the difference in the complexity of the algorithms (P = .71).

CONCLUSIONS

The GPU-accelerated volume subdivision technique was as accurate as the B-spline technique and required significantly less processing time. The GPU-accelerated volume subdivision technique may enable the implementation of nonrigid registration into routine clinical practice.

Breath-hold three-dimensional CT of the liver with multi-detector row helical CT

PURPOSE

To compare image quality on transverse source images and coronal and sagittal reformations to determine the feasibility of using single-breath-hold three-dimensional liver computed tomography (CT) with multi-detector row helical CT in patients suspected of having hepatic metastases.

MATERIALS AND METHODS

Fifty-three patients underwent the protocol. Coronal and sagittal reformations were constructed. Images were reviewed for duration of scan acquisition and length and adequacy of z-axis coverage. Reformations were scored for visualization of portal and hepatic vein branches, liver edge sharpness, cardiac pulsation and respiratory motion artifacts, noise due to mottle, and overall impression.

RESULTS

Mean z-axis coverage was 207 mm +/- 33 (SD) (range, 145-280 mm), with a mean acquisition time of 10.96 seconds +/- 1.78 (range, 7.73-14.93 seconds). In 44 (83%) patients, the entire liver was imaged on a single helical scan. Artifact from cardiac motion was not identified on the transverse source images in any patient but was identified on coronal images in eight (15%) and on sagittal images in seven (13%). Similarly, noise due to mottle was not identified on the transverse source images but was identified on coronal images in seven (13%) patients and on sagittal images in six (11%).

CONCLUSION

It is feasible to perform single-breath-hold three-dimensional liver CT with multi-detector row helical CT technology. Reformations provide a unique perspective with which to view the liver and may improve diagnostic capacity.

Power injection of contrast media using central venous catheters: feasibility, safety, and efficacy

OBJECTIVE

This study evaluates the feasibility, safety, and efficacy of power-injecting IV contrast media through central venous catheters for CT examinations.

SUBJECTS AND METHODS

Two hundred ninety-five CT examinations were performed during an 18-month period in 225 patients with indwelling central venous catheters. Patients were randomized to power injection either through peripheral IV catheter or through central venous catheter. Feasibility was defined as the percentage of patients with contrast material injected successfully through the randomized access route. Safety was evaluated by comparing patients with complications. Efficacy was evaluated by comparing contrast enhancement of the thoracic aorta, pulmonary artery, abdominal aorta, and liver.

RESULTS

Two hundred nine patients had randomization data recorded. One hundred three (94%) of 109 patients were successfully injected through their indwelling catheter compared with 42 (42%) of 100 through a peripherally placed IV catheter (p < 0.001). After reassignment for unsuccessful access, 174 patients underwent central venous catheter injection, and 51, peripheral IV catheter injection. No statistically significant difference was noted in the complications between the central venous catheter and peripheral IV catheter groups. Enhancement was greater in the thoracic aorta, pulmonary artery, and liver for the peripheral IV catheter group (p < 0.03).

CONCLUSION

Power injection of contrast media through central venous catheters for CT examinations is feasible and safe when set hospital guidelines and injection protocols are followed. This technique provides an acceptable alternative in patients without adequate peripheral IV access when bolus contrast enhancement is desired.

Computed tomography scan of the liver

Computed tomography (CT) examination of the liver has continually been improving our understanding and assessment of liver disease since its introduction into clinical practice. The hallmark of the advances in CT imaging has undoubtably been helical CT, which made a great impact on body imaging with its many advantages, the most important being optimization of multiphasic enhanced studies, CT hepatic angiography (CTHA), and CT arterial portography (CTAP). Various applications and protocols of CT imaging rendering advantages and drawbacks to the technique are highlighted in this review article.

Effects of injection rates of contrast material on arterial phase hepatic CT

OBJECTIVE

Our goal was to assess the effects of the i.v. injection rate of contrast material on arterial phase hepatic CT.

SUBJECTS AND METHODS

One hundred patients were randomly divided into four groups of 25 with different injection rates of 90 ml of contrast material: 2, 3, 4, or 5 ml/sec. Single-level serial CT was performed at the level of the middle section of the main portal vein before injection and every 2 sec from 12 sec to 60 sec after injection of contrast material. The enhancement value was calculated as the difference in attenuation value between the unenhanced and contrast-enhanced images for the aorta and liver parenchyma. The duration of the arterial phase was defined as the interval beginning when the enhancement value for the aorta reached 100 H and ending when the value for the liver parenchyma reached 20 H.

RESULTS

Faster injection rates increased the maximum enhancement of the aorta. Although faster injection rates decreased the time from injection to the beginning and the end of the arterial phase, faster injection rates did not decrease the duration of the arterial phase itself.

CONCLUSION

A faster injection rate increases arterial enhancement of the liver, and the duration of the arterial phase remains the same as that occurring with a slower injection rate. We hypothesize that faster injection rates can provide better results using CT to reveal hypervascular liver tumors.

Hepatic metastases

Developments in ultrasound, CT scan, and MR imaging have increased our ability to detect and characterize focal liver lesions. Advances in the medical and surgical treatment of secondary liver tumors have continued to challenge these advances in radiology. A successful outcome depends on knowledge of the size and location of the tumor burden, and accurate radiologic assessment is crucial to identify those subgroups who may benefit from surgery and to prevent unnecessary radical surgery in those likely to gain only a short-term benefit.

Application of pharmacokinetics to computed tomography: injection rates and schemes: mono-, bi-, or multiphasic?

OBJECTIVE

The objective of the current study was to test whether optimization of dose regimens for detecting focal liver lesions by computed tomography is possible by using the available time-density data of former studies published in the literature and a computer program so that the number of further clinical tests with the exclusive objective of optimizing injection schemes could be reduced.

METHODS

Computed tomography enhancement data of the aorta and/or the liver obtained after injecting a conventional ionic and a nonionic contrast agent were used to calculate pharmacokinetic parameters and to simulate the time course of enhancement for a variety of different infusion regimens modifying contrast medium strength, dose, and injection rate. The study consisted of two parts. In the first part, mean relative enhancement curves of the aorta and of liver parenchyma (0 to 300 sec) using meglumine diatrizoate (306 mg iodine per mL, 300 mg iodine per kg) were taken from the literature and their values were approximated using the computer program TOPFIT. In the second part, equivalent data for iohexol including a total of three strengths (240, 300, and 350 mg iodine per kg) and doses from 30 to 45 grams of iodine were used. "Validation" of the simulation method was obtained, first by comparing measured and calculated maximum intensities and times to reach maximum and, second, by using one injection scheme for the simulation of a second and comparing the results with actually measured data.

RESULTS

The computer program TOPFIT allowed for excellent curve fitting of the measured density values. The data obtained in the first part of the study showed that after a dose of 300 mg I/kg and a rate of 2 mL/sec maximal enhancement is achieved in the aorta after 30 seconds (approximately 100 HU) and in the liver after 50 seconds (approximately 30 HU). The higher the dose and the rate of infusion were, the higher was the enhancement. The difference in density between aorta and liver was proportional to the infusion rate approaching asymptotically approximately 90 HU at 8 mL/sec for a dose of 300 mg I/kg. Bi- or triphasic infusion schemes did not improve differences in enhancement. The curve fitting obtained in the second part of the study also confirmed the results reported in the literature. A "crossover" prediction of data was possible within the range of interindividual variations of pharmacokinetic parameters and thus validated the chosen approach of computer simulation. Furthermore, data sets selected randomly out of the simulation results could be used--within the limits of interindividual variability--to predict data determined in other clinical trials.

CONCLUSION

The computer program TOPFIT appears useful for the optimization of time--density profiles in computed tomography. The number of further clinical studies with the objective of optimization could therefore possibly be reduced.

Characterization of focal hepatic tumors. Value of two-phase scanning with spiral computed tomography

BACKGROUND

Spiral computed tomography (CT) allows imaging of the liver during the peak contrast material levels due to the capability of fast data acquisition. The objective of this study was to evaluate the usefulness of two-phase spiral CT in the differential diagnosis of focal hepatic tumors.

METHODS

One hundred two patients who had hepatic tumors (211 nodules; 149 hepatocellular carcinomas [HCCs], 36 metastases, and 26 hemangiomas) underwent two-phase spiral CT with 10-mm collimation at 10 mm/second table speed and 120 mL of contrast material injected at the rate of 3 mL/second. Computed tomography images of the hepatic arterial phase and late (equilibrium) phase were obtained at 35-second and 180-second delays, respectively. The enhancement patterns of tumors were divided into six types and were compared with the attenuation of surrounding liver parenchyma: totally high, peripherally high, centrally high, mixed, iso, and low.

RESULTS

The common enhancement patterns of HCC in two-phase spiral CT were totally high in the arterial phase and low (n = 63, 42%) or iso (n = 28, 19%) in the late phase. Metastasis showed peripherally nonnodular high attenuation (n = 9, 25%) or low attenuation (n = 9, 25%) in the arterial phase and low attenuation in the late phase, followed by totally high attenuation in the arterial phase and iso in the late phase (n = 6, 17%). Hemangiomas showed totally or peripherally nodular enhancement in the arterial and late phases (n = 23, 89%). In distinguishing hemangiomas from malignant tumors, totally high or peripherally nodular high attenuation in the late phase was the most useful contrast enhancement pattern (96% of hemangioma vs. 0% of malignant tumors). In distinguishing HCCs from metastases, a combination of contrast enhancement pattern of totally high attenuation in the arterial phase and low in the late phase was the most useful contrast enhancement pattern (42% of HCCs vs. 0% of metastases). The predictability of differentiation between hemangiomas and malignant tumors and between HCCs and metastases was 99% and 90% with spiral CT, respectively.

CONCLUSIONS

Two-phase spiral CT is useful in the differential diagnosis of focal hepatic tumors with evaluation of contrast enhancement patterns.

Comparison of iohexol-240 versus iohexol-300 in abdominal CT

Forty patients without evidence of liver, kidney, or significant cardiac disease were prospectively divided into two groups of 20, receiving either iohexol-240 or iohexol-300. A contrast load of 150 ml was administered in conjunction with a rapid scanning technique at a preselected, fixed level to include liver, renal cortex, and aorta. Peak enhancement was calculated as change in Hounsfield units (HU) over baseline for each area of interest. Mean peak enhancement and standard deviation were calculated for each organ, and the difference between the means for the two contrast agents was compared using the Student's t test. Differences were not statistically significant with all p values greater than 0.05. Our results suggest iohexol-240 is preferred to iohexol-300 for body computed tomography (CT) due to its lower cost and iodine load without statistically significant change in diagnostic quality of the examination.

Liver CT: a practical approach to dynamic contrast enhancement

The aim of this study was to establish a practical, simple protocol that reliably produces high quality dynamic incremental computed tomography (CT) of the liver. We reviewed 90 patients randomly allocated into six different protocols. All had preliminary unenhanced scans followed by a dynamic incremental CT of the liver. An initial delay of 30 seconds was used from the commencement of the injection of Iopamiro 370. The groups were: 1. Pump infusion (a) 100 mls at 2 mls/sec scanning inferosuperiorly. (b) 100 mls at 2 mls/sec scanning superoinferiorly. (c) 100 mls at 1 ml/sec scanning inferosuperiorly. (d) 50 mls at 1 ml/sec scanning inferosuperiorly. 2. 40 mls hand injected bolus followed immediately by 60 ml pump infusion at 1.3 mls/sec scanning inferosuperiorly. 3. 50 mls hand injected bolus scanning inferosuperiorly. The parameters recorded were the degree of hepatic parenchymal and hepatic venous enhancement and the aortic--IVC difference at the last slice through the liver, all measured in Hounsfield units. The protocols using 100 mls of contrast produced approximately twice the parenchymal and hepatic venous enhancement compared with those using 50 mls. Approximately 60-90% of examinations using 100 mls produced scans through the entire liver during the bolus or nonequilibrium phase, deemed the most sensitive for the detection of focal lesions, compared with 13-33% of those using 50 mls. Equally satisfactory results were obtained using the relatively inexpensive Biotel power injector preceded by a 40 ml hand injected bolus, compared with using an Angiomat angiography infusion pump.(ABSTRACT TRUNCATED AT 250 WORDS)

Imaging prior to second-look surgery for carcinoma

Technical advances in imaging are barely keeping pace with the need for detailed pre-operative imaging in second-look surgery. Although the majority of intra-abdominal recurrence can be detected at surgery, pre-operative knowledge of possible sites of involvement will provide more efficient use of operative time. Dynamic incremental bolus CT is the modality of choice when evaluating these patients, even though magnetic resonance imaging is approaching, and may exceed, computed tomography in utility in the abdomen. Monoclonal antibody radioimmunoscintigraphy is useful for extra-abdominal sites of recurrence. Further technical advancement is needed to make it useful in the abdomen.

Review of hepatic imaging and a problem-oriented approach to liver masses

We believe that imaging of the liver is complicated. The sporadic appearance of incidental benign lesions and variability in scanning techniques, equipment and artifacts add difficulties to the evaluation of liver masses. Therefore we emphasize the need to define the problem for which the patient is being imaged. This information helps in choosing the procedure of choice and the technique needed to give the most expedient, accurate answer. This will also help apply the lowest risk and most cost-efficient care. Imaging algorithms vary depending on the suspected pathological conditions. Dynamic bolus-enhanced CT is the modality of choice in most situations. Tc99m sulfur-colloid liver-spleen scans are helpful in patients with suspected FNH, and Tc99m-tagged-RBC-SPECT scans are recommended to confirm cavernous hemangiomas. Cysts are easily confirmed by US. Although MRI is competitive with CT, it has not become a primary modality because of cost, availability, patient selection and variability of scanner capabilities among the many manufacturers and models. It is hard to predict what future development of imaging techniques will bring. Many feel that significant advances have plateaued. Time and money will more likely be concentrated on improving image resolution, speed of scanning and ability to transfer this information to sites outside of the radiology department. In addition to faster scanning, we expect to soon have available safe intravenous and enteric contrast agents for MRI. Certainly this will lead to a new round of investigations to compare MRI with CT scanning.