To evaluate two methods for reducing metal artifacts in computed tomography (CT)--the metal deletion technique (MDT) and the selective algebraic reconstruction technique (SART)--and compare these ...methods with filtered back projection (FBP) and linear interpolation (LI).
The institutional review board approved this retrospective HIPAA-compliant study; informed patient consent was waived. Simulated projection data were calculated for a phantom that contained water, soft tissue, bone, and iron. Clinical projection data were obtained retrospectively from 11 consecutively identified CT scans with metal streak artifacts, with a total of 178 sections containing metal. Each scan was reconstructed using FBP, LI, SART, and MDT. The simulated scans were evaluated quantitatively by calculating the average error in Hounsfield units for each pixel compared with the original phantom. Two radiologists who were blinded to the reconstruction algorithms used qualitatively evaluated the clinical scans, ranking the overall severity of artifacts for each algorithm. P values for comparisons of the image quality ranks were calculated from the binomial distribution.
The simulations showed that MDT reduces artifacts due to photon starvation, beam hardening, and motion and does not introduce new streaks between metal and bone. MDT had the lowest average error (76% less than FBP, 42% less than LI, 17% less than SART). Blinded comparison of the clinical scans revealed that MDT had the best image quality 100% of the time (95% confidence interval: 72%, 100%). LI had the second best image quality, and SART and FBP had the worst image quality. On images from two CT scans, as compared with images generated by the scanner, MDT revealed information of potential clinical importance.
For a wide range of scans, MDT yields reduced metal streak artifacts and better-quality images than does FBP, LI, or SART.
http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11101782/-/DC1.
Several recently introduced ‘new’ techniques in computed tomography—iterative reconstruction, gated cardiac CT, multiple-source, and dual-energy CT—actually date back to the early days of CT. We ...review the historic origins and evolution of these techniques, which may provide some insight into the latest innovations in commercial CT systems.
CT artifacts: causes and reduction techniques Boas, F Edward; Fleischmann, Dominik
Imaging in Medicine,
2012-April-01, 2012-04-00, 20120401, Letnik:
4, Številka:
2
Journal Article, Book Review
Recenzirano
Artifacts are commonly encountered in clinical CT and may obscure or simulate pathology. There are many different types of CT artifacts, including noise, beam hardening, scatter, pseudoenhancement, ...motion, cone-beam, helical, ring and metal artifacts. We review the cause and appearance of each type of artifact, correct some popular misconceptions and describe modern techniques for artifact reduction. Noise can be reduced using iterative reconstruction or by combining data from multiple scans. This enables lower radiation dose and higher resolution scans. Metal artifacts can also be reduced using iterative reconstruction, resulting in a more accurate diagnosis. Dual- and multi-energy (photon counting) CT can reduce beam hardening and provide better tissue contrast. Methods for reducing noise and out-of-field artifacts may enable ultra-high resolution limited field of view imaging of tumors and other structures.
Preclinical testing of new locoregional therapies for pancreatic cancer has been challenging, due to the lack of a suitable large animal model.
To develop and characterize a porcine model of ...pancreatic cancer. Unlike small animals, pigs have similar physiology, drug dosing, and immune response to humans. Locoregional therapy in pigs can be performed using the same size catheters and devices as in humans.
The Oncopig is a transgenic pig with Cre-inducible TP53R167H and KRASG12D mutations. In 12 Oncopigs, CT-guided core biopsy of the pancreas was performed. The core biopsy was incubated with an adenoviral vector carrying the Cre recombinase gene. The transformed core biopsy was injected back into the pancreas (head, tail, or both). The resulting tumors (n = 19) were characterized on multi-phase contrast-enhanced CT, and on pathology, including immunohistochemistry. Angiographic characterization of the tumors was performed in 3 pigs.
Pancreatic tumors developed at 19 out of 22 sites (86%) that were inoculated. Average tumor size was 3.0 cm at 1 week (range: 0.5-5.1 cm). H&E and immunohistochemical stains revealed undifferentiated carcinomas, similar to those of the pancreatobiliary system in humans. Neoplastic cells were accompanied by a major inflammatory component. 1 of 12 pigs only had inflammatory nodules without evidence of neoplasia. On multiphase CT, tumors were hypovascular compared to the normal pancreas. There was no pancreatic duct dilation. In 3 pigs, angiography was performed, and in all 3 cases, the artery supplying the pancreatic tumor could be catheterized using a 2.4 F microcatheter. Selective angiography showed the pancreatic tumor, without extra-pancreatic perfusion.
Pancreatic cancer can be induced in a transgenic pig. Intra-arterial procedures using catheters designed for human interventions were technically feasible in this large animal model.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•In transgenic pigs carrying KRASG12D and TP53R167H Cre-inducible mutations, AdCre percutaneous and endovascular inoculations induced neoplastic lung nodules in 2/6 and 1/10 attempts, ...respectively.•All lung tumors were visible at the 1-week computed tomography, and appeared as well-circumscribed solid nodules, with a median longest diameter of 14 mm (range: 5–27 mm).•Tumors consisted of inflammatory undifferentiated neoplasms composed of atypical spindle and epithelioid cells and/or a fibrovascular stroma and abundant mixed leukocytic infiltrate. Atypical cells diffusely displayed expression of vimentin and some showed expression of CK WSS and CK 8/18.
Lung cancer models in large animals are lacking. Oncopigs are transgenic pigs that carry both KRASG12D and TP53R167H Cre-inducible mutations. This study aimed to develop and histologically characterize a swine model of lung cancer that could serve for preclinical studies evaluating locoregional therapies.
In two Oncopigs, an adenoviral vector encoding the Cre-recombinase gene (AdCre) was injected endovascularly through the pulmonary arteries or inferior vena cava. In two other Oncopigs, a lung biopsy was performed and incubated with AdCre, before reinjecting the mixture into the lungs percutaneously. Animals were clinically and biologically (complete blood count, liver enzymes and lipasemia) monitored. Obtained tumors were characterized on computed tomography (CT) and on pathology and immunohistochemistry (IHC).
Neoplastic lung nodules developed following 1 (1/10, 10%) endovascular inoculation, and 2 (2/6, 33%) percutaneous inoculations. All lung tumors were visible at the 1-week CT, and appeared as well-circumscribed solid nodules, with a median longest diameter of 14 mm (range: 5–27 mm). Only one complication occurred: an extravasation of the mixture into the thoracic wall during a percutaneous injection that resulted in a thoracic wall tumor. Pigs remained clinically healthy during the entire follow-up (14–21 days). On histology, tumors consisted of inflammatory undifferentiated neoplasms composed of atypical spindle and epithelioid cells and/or a fibrovascular stroma and abundant mixed leukocytic infiltrate. On IHC, atypical cells diffusely displayed expression of vimentin and some showed expression of CK WSS and CK 8/18. The tumor microenvironment contained abundant IBA1 + macrophages and giant cells, CD3 + T cells, and CD31 + blood vessels.
Tumors induced in the lungs of Oncopigs are fast growing poorly differentiated neoplasms associated with a marked inflammatory reaction that can be easily and safely induced at site specific locations. This large animal model might be suitable for interventional and surgical therapies of lung cancer.
Liver metastases are a major cause of death from colorectal cancer. Intraarterial therapy options for colorectal liver metastases include chemoinfusion via a hepatic arterial pump or port, ...irinotecan-loaded drug-eluting beads, and radioembolization using
Y microspheres. Intraarterial therapy allows the delivery of a high dose of chemotherapy or radiation into liver tumors while minimizing the impact on liver parenchyma and avoiding systemic effects. Specificity in intraarterial therapy can be achieved both through preferential arterial flow to the tumor and through selective catheter positioning. In this review, we discuss indications, contraindications, preprocedure evaluation, activity prescription, follow-up, outcomes, and complications of radioembolization of colorectal liver metastases. Methods for preventing off-target embolization, increasing the specificity of microsphere delivery, and reducing the lung-shunt fraction are discussed. There are 2 types of
Y microspheres: resin and glass. Because glass microspheres have a higher activity per particle, they can deliver a particular radiation dose with fewer particles, likely reducing embolic effects. Glass microspheres thus may be more suitable when early stasis or reflux is a concern, in the setting of hepatocellular carcinoma with portal vein invasion, and for radiation segmentectomy. Because resin microspheres have a lower activity per particle, more particles are needed to deliver a particular radiation dose. Resin microspheres thus may be preferable for larger tumors and those with high arterial flow. In addition, resin microspheres have been approved by the U.S. Food and Drug Administration for colorectal liver metastases, whereas institutional review board approval is required before glass microspheres can be used under a compassionate-use or research protocol. Finally, radiation segmentectomy involves delivering a calculated lobar activity of
Y microspheres selectively to treat a tumor involving 1 or 2 liver segments. This technique administers a very high radiation dose and effectively causes the ablation of tumors that are too large or are in a location considered unsafe for thermal ablation. The selective delivery spares surrounding normal liver, reducing the risk of liver failure.
Lung cancer is the leading cause of cancer mortality in the world. A significant proportion of patients with lung cancer are not candidates for surgery and must resort to other treatment ...alternatives. Rapid technological advancements in fields like interventional radiology have paved the way for valid treatment modalities like image-guided percutaneous and transarterial therapies for treatment of both primary and metastatic lung cancer. The rationale of ablative therapies relies on the fact that focused delivery of energy induces tumor destruction and pathological necrosis. Image-guided percutaneous thermal ablation therapies are established techniques in the local treatment of hepatic, renal, bone, thyroid, or uterine lesions. In the lung, the 3 main indications for lung ablation include local curative intent, a strategy to achieve a chemoholiday in oligometastatic disease, and recently, oligoprogressive disease. Transarterial therapies include a set of catheter-based treatments that involve delivering embolic and/or chemotherapeutic agents directed into the target tumor via the supplying arteries. This article provides a comprehensive review of the various techniques available and discusses their applications and associated complications in primary and metastatic lung cancer.
•Virtual injection accurately simulated selective arterial injection and was ranked as clinically relevant in 89.2% ± 0.5 of investigated vessels.•Interobserver agreement was substantial with a ...Fleiss’ kappa = 0.79 (95% confidence interval = 0.73–0.84).
To assess the accuracy, sensitivity, positive predictive value (PPV) and interobserver agreement of a virtual injection (VI) software that simulates selective arterial injection from nonselective cone-beam CT (CBCT) arteriography.
From March 2019 to May 2020, 20 consecutive patients in whom a nonselective injected CBCT and a selective CT angiography (CTA) were completed in the same procedure, were retrospectively included. The position of the microcatheter tip used for selective CTA injection was identified. The VI was simulated from the exact same point on the nonselective CBCT and the two volumes were merged. VI was compared to the real injection on the selective CTA. Three interventional radiologists evaluated the accuracy using a 6-point scale (Perfect; Good; Fair; Incorrect Origin; False Negative; Non existing). Sensitivity, PPV, and Fleiss’ kappa were calculated. Numerical variables were presented as means ± standard deviations.
Twenty procedures and 195 vessel segments were analyzed. Most vessels were 4th order (57/195; 29%) and 5th order (96/195; 49%). VI was classified as perfect to good in 96.8% ± 1.4 of 1st–3rd order arteries and in 83.4% ± 0.4 of 4th–5th order arteries. Interobserver agreement was substantial (Fleiss’ kappa = 0.79; 95% confidence interval = 0.73–0.84, P < 0.01). False negatives were reported with a mean of 9.4% ± 0.3. Average sensitivity was 90.6% ± 0.3 and average PPV was 92.7% ± 0.02. Fourteen false positives were noted.
CBCT-based VI software accurately simulated distal injections in the liver with high sensitivity and a substantial interobserver agreement.
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