Imaging Pearls ❯ Liver ❯ Protocols and Techniques
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"Image noise increased from 5.7 to 11.4 HU as the tube voltage decreased from 140 to 80 kVp resulting in a significantly lower image quality score (4.0 vs 3.0) with protocol B according to all readers. At the same time protocol B yielded significantly higher CNR and lesion conspicuity scores than protocol A, along with a lower effective dose (5.1 vs 17.5 mSv)"
Hypervascular Liver Tumors: Low Tube Voltage, High Tube Current Multidetector CT during Late Hepatic Arterial Phase for Detection-Initial Clinical Experience
Marin D et al.
Radiology 2009; 251:771-779conclusion
Lower kVp studies increase the "brightness" of vascular lesions while increasing image noise and giving a general lower image quality. However the doses may be 50% or gretaer lower with the lower kVp- " In our study, using abdominal 64-MDCT in pediatric patients, we found that approximately 1.5 mL/kg, or 0.525 g l/kg, yields 116 HU of hepatic attenuation or 50-55 HU of hepatic enhancement."
Aortic and Hepatic Contrast Enhancement with Abdominal 64-MDCT in Pediatric Patients: Effect of Body Weight and Iodine Dose
Bae KT et al
AJR 2008; 191:1589-1594 - "Approximately 0.5 g I/kg is needed to achieve the maximum hepatic enhancement of 50 HU; that is, 35 g I for a 70-kg patient."
Aortic and Hepatic Contrast Enhancement with Abdominal 64-MDCT in Pediatric Patients: Effect of Body Weight and Iodine Dose
Bae KT et al
AJR 2008; 191:1589-1594 - "In general, 50 HU is considered to be a diagnostically appropriate level of hepatic enhancement for abdominal CT in adult patients."
Aortic and Hepatic Contrast Enhancement with Abdominal 64-MDCT in Pediatric Patients: Effect of Body Weight and Iodine Dose
Bae KT et al
AJR 2008; 191:1589-1594 - "The average reading time for the combined interpretation of transverse and coronal image sets (mean 12.1 ± 0.8 minutes) was significantly longer than for the transverse image set (7.4 ± 1.5 minutes) or the coronal image set (7.1 ± 1.3 minutes) ."
Detection of Hepatocellular Carcinoma in Patients with Cirrhosis: Added Value of Coronal Reformations from Isotrophic Voxels with 64-MDCT
Marin D et al.
AJR 2009; 192:180-187 - "With 64-MDCT, the addition of isotrophic coronal reformations to transverse images significantly improved reader confidence for the detection of HCC, with no statistically significant improvement in sensitivity, positive predictive value, or diagnostic accuracy. This improvement comes at the cost of a longer interpretation time."
Detection of Hepatocellular Carcinoma in Patients with Cirrhosis: Added Value of Coronal Reformations from Isotrophic Voxels with 64-MDCT
Marin D et al.
AJR 2009; 192:180-187 - CT Evaluation of a Liver Mass
- Enhancement characterization
Arterial phase
- Does it have a feeding artery and if does would you describe it as smooth or irregular?
- Is the feeding vessel enlarged?
- Is there neovascularity?
- "The administration of a total iodine dose of 525 mg or more per kilogram of body weight is desirable for the good or excellent depiction of hypervascular HCC, although the administration of 450 mg I/kg of body weight can depict hypervascular HCC."
Optimal Contrast Dose for Depiction of Hypervascular Hepatocellular Carcinoma at Dynamic 64-MDCT
Yanaga Y et al.
AJR 2008; 190:1003-1009
- "The administration of a total iodine dose of 525 mg or more per kilogram of body weight is desirable for the good or excellent depiction of hypervascular HCC, although the administration of 450 mg I/kg of body weight can depict hypervascular HCC."
Optimal Contrast Dose for Depiction of Hypervascular Hepatocellular Carcinoma at Dynamic 64-MDCT
Yanaga Y et al.
AJR 2008; 190:1003-1009
(Omnipaque-350 350 mg/ml of iodine so to get 525 mg iodine you need 150 ml or so)
- "In MDCT, reducing the amount of contrast medium does not affect aortic enhancement in the early arterial phase but decreases hepatic enhancement at the portal phase. Greater than 1.5 mL/kg reduction in the dose of contrast medium followed by saline flushing may not be advisable for liver CT in low and medium weight patients."
Assessment of the Use of a Saline Chaser to Reduce the Volume of Contrast Medium in Abdominal CT Orlandini F et al. AJR 2006; 187:511-515.
- "In MDCT, reducing the amount of contrast medium does not affect aortic enhancement in the early arterial phase but decreases hepatic enhancement at the portal phase."
Assessment of the Use of a Saline Chaser to Reduce the Volume of Contrast Medium in Abdominal CT Orlandini F et al. AJR 2006; 187:511-515.
- " When MDCT of the liver is performed using fixed timing delays, maximal vascular and hepatic parenchymal enhancement is achieved on either late arterial phase or portal venous phase imaging. In most patients, early arterial phase imaging does not improve tumor conspicuity by either quantitative or subjective analysis."
MDCT of the Liver and Hepatic Neoplasms: Effect of Multiphasic Imaging on Tumor Conspicuity and Vascular Enhancement Francis IR et al. AJR 2003;180:1217-1224
- "Although the arterial enhancement is superior in the late arterial phase, some venous contamination occurs, which makes for the early arterial phase more suitable for CT angiography."
MDCT of the Liver and Hepatic Neoplasms: Effect of Multiphasic Imaging on Tumor Conspicuity and Vascular Enhancement Francis IR et al. AJR 2003;180:1217-1224
- "A new paradigm for rapid hepatic CT acquisition- namely, hepatic arterial, portal vein inflow (or late arterial phase), and hepatic venous phases- is recommended to replace hepatic artery dominant and portal venous phases."
Multiphase Helical CT with a Multirow Detector CT Scanner Foley WD et al. AJR 2000;175: 879-685
- MDCT of the Liver
- Non-contrast CT : 0 seconds
- Early arterial phase : 15 seconds
- Late arterial phase : 25-30 seconds
- Portal venous phase : 50-55 seconds
- Late portal venous phase : 70-90 seconds
- Delayed phase : 4-10 minutes
- CT with Arterial Portography and Hepatic Arteriography
- Place catheters both in the SMA and common hepatic artery
- Arterial portography with injection into SMA was done first and
- Hepatic Arteriography was performed with hepatic artery injected after a five minute delay
- "Multiplanar volume rendering and maximum intensity projection of multislice computed tomography data allow for robust evaluation of the hepatic parenchyma, with early detection of neovascularity and tumor stain, and enable better assessment of the tumor burden compared with routine axial images. Lesion characterization can also potentially improve."
Incremental Value of Advanced Image Processing of Multislice Computed Tomography Data in the Evaluation of Hypervascular Liver Lesions Kamel IR et al. J Comput Assist Tomogr 27(4):652-656
- Blunt Hepatic Trauma: Spectrum of Injuries
- Laceration
- Suncapsular hematoma
- Parenchymal hematoma
- Active hemorrhage
- Venous injuries
- Arterial Phase Imaging: Factors impacting the selection of the Scan Delay
- Contrast volume
- Injection rate
- 4 vs 16 vs 64 detector MDCT
- Total scan time needed
- Axial vs. MPR and VRT acquisition (3mm x 3mm or .75 mm x .50 mm)
- JHU Scan Protocol for 64 MDCT
- Arterial phase imaging of the liver begins at 25-30 sec post start of contrast injection using 100 ml of contrast injected at 4 cc/sec