Customizing Contrast Injection for Body MDCT: Algorithmic Approach Lincoln L. Berland, M.D., F.A.C.R. University of Alabama at Birmingham
Before Contrast
Prep and Hydration Hydration single most important factor: To get adequate collecting system filling To limit nephrotoxicity Don't keep patient NPO (clear liquids in am) Lots of water prior to scan
Intravenous Contrast Parameters Contrast or not? Route - IV arm, central line, hand, foot Concentration Volume Rate Saline chaser Fixed, bolus tracking, test bolus
Principles of Intravenous Contrast Dynamics
General - Iodine Dose If increase dose of Iodine, but inject within same duration: Increases peak enhancement Does not change time at which peak occurs How to achieve this: Increase contrast concentration, or Increase injection rate, maintain injection duration (more contrast volume)
Iodine Concentration Selection Higher concentration: can inject more Iodine for a specific volume/second Equivalent to increasing injection rate if you don t increase concentration With higher concentration, can decrease the volume injection rate for given Iodine injection rate Therefore, 350-400 mg I/mL preferred over 300 mg I/mL
Aorta, Liver by Rate If increase injection rate, but keep Iodine dose constant: Aortic enhancement peak increases continuously with rate Liver enhancement peak levels off above 1.5 ml/sec
Aorta, Liver Enhancement MYTH: Can decrease contrast dose for liver scan by increasing injection rate TRUTH: Can decrease contrast dose for CTA by increasing injection rate
Injection Duration TIME to peak aortic and liver enhancement depends most strongly on injection duration Peak enhancement usually occurs shortly after injection completed
Injection Duration MYTH: For body scans, can use fixed scan delay regardless of injection rate TRUTH: Enhancement curves vary greatly by patient Use bolus tracking for arterial studies Fixed delay (by duration) usually OK for liver, etc.
Scan Delay MYTH: Faster scanner (e.g. 64 vs. 4- slice), shorter delay to scanning TRUTH: Faster scanner, longer delay to begin scanning Peak doesn t change, but more likely to finish scan before peak occurs Downslope of enhancement not as fast as upslope, so better to scan a little late rather than early
Patient-Specific Factors
Patient Weight - Enhancement Hepatic and arterial enhancement are proportional to Iodine dose administered and inversely proportional to weight Time to the enhancement peak is affected little by weight Therefore, Iodine dose should be increased proportional to weight
Cardiac Output - Aorta As cardiac output decreases, delay to peak increases MYTH: As cardiac output decreases, enhancement decreases TRUTH: Decreased cardiac output increases enhancement Therefore, decrease Iodine dose with decreased cardiac function
Cardiac Output - Hepatic As cardiac output decreases, delay to hepatic enhancement increases 60% decrease in cardiac output can delay peak from baseline 60 seconds to 150 seconds MYTH: Decreased cardiac output affects peak hepatic enhancement TRUTH: Hepatic enhancement won t change, but later peak
Phase by Application Consequence of these effects is that you must consider the target organ(s) to best design protocols, e.g.: Earlier scan for aorta Slower scan for runoff Later scan for liver
Contrast - From Theory to Practice
Iodine Dose Selection Patient weight Renal and cardiac function Brand and concentration of contrast available Organ and body region
Iodine Dose Selection Base dose varies from 30-60 gm Iodine Should select based on Iodine dose, not volume We recommend standard dose based of 42 gm Iodine for average weight patient Select by patient weight, other factors
Iodine Dose Selection Some select: ml/kg If vary continuously by weight: Should be: gm I/kg We prefer weight categories for the average patient
Contrast Injection Rate Selection Route of injection Adequacy of line Injector - Dual Head with saline chaser better uses contrast injected Speed of scanner
Scan Timing Selection Specific application (e.g. 3-phase, routine, etc.) Speed of scanner
Algorithm Weight +concentration of agent + application: Volume Volume + application + adequacy of IV: Injection rate Injection rate + volume: Injection duration Injection duration + application + scanner: Scan timing
Contrast Dose Selection Select Contrast Dose Weight 45-60 kg (100-130 lb) 65-90 kg (140-200 lbs) 90-110 kg (200-240 lb) >110 kg (>240 lb) Body CT Based on 42 gi for average patient 350 mg/ml 350 mg/ml Š Renal insufficiency Contrast Volume 85 ml 120 ml 150 ml 180 ml Weight 45-60 kg (100-130 lb) 60-90 kg (130-200 lbs) 90-110 kg (200-240 lb) >110 kg (>240 lb) Body CT Select Contrast Dose Based on 42 gi for average patient 370 mg/ml 370 mg/ml Š Renal insufficiency Contrast Volume 85 ml 115 ml 140 ml 175 ml Weight 45-60 kg (100-130 lb) 65-90 kg (140-200 lbs) >90 kg (>200 lb) Contrast Volume 56 ml 80 ml 100 ml Weight 45-60 kg (100-130 lb) 65-90 kg (140-200 lbs) >90 kg (>200 lb) Contrast Volume 55 ml 75 ml 90 ml
Contrast Dose Selection Body CT Select Contrast Dose Based on 52 gi for average patient Weight 45-60 kg (100-130 lb) 65-90 kg (140-200 lbs) 90-110 kg (200-240 lb) >110 kg (>240 lb) 350 mg/ml 350 mg/ml Š Renal insufficiency Contrast Volume 104 ml 148 ml 185 ml 200 ml* Body CT Select Contrast Dose Based on 52 gi for average patient Weight 45-60 kg (100-130 lb) 60-90 kg (130-200 lbs) 90-110 kg (200-240 lb) >110 kg (>240 lb) 370 mg/ml 370 mg/ml Š Renal insufficiency Contrast Volume 98 ml 140 ml 175 ml 200 ml* Weight 45-60 kg (100-130 lb) 65-90 kg (140-200 lbs) >90 kg (>200 lb) Contrast Volume 56 ml 80 ml 100 ml Weight 45-60 kg (100-130 lb) 65-90 kg (140-200 lbs) >90 kg (>200 lb) Contrast Volume 55 ml 75 ml 90 ml Notes: *Calculated volume for high weight exceeds 200 ml capacity of injector. Renal insufficiency dose based on 42 gi chart rather than 52 gi chart. Notes: *Calculated volume for high weight exceeds 200 ml capacity of injector. Renal insufficiency dose based on 42 gi chart rather than 52 gi chart.
Contrast Injection Rate Body CT (excluding CTAs) Select Injection Rate All contrast agents Routine injection duration Injection Volume Injection Rate Injection Duration 46-50 ml 1.6 ml/sec 30 seconds 51-55 ml 1.8 ml/sec 30 seconds 56-60 ml 2.0 ml/sec 30 seconds 61-65 ml 2.1 ml/sec 30 seconds 66-70 ml 2.3 ml/sec 30 seconds 71-75 ml 2.5 ml/sec 30 seconds 76-80 ml 2.6 ml/sec 30 seconds 81-85 ml 2.8 ml/sec 30 seconds 86-90 ml 3.0 ml/sec 30 seconds 91-95 ml 3.1 ml/sec 30 seconds 96-100 ml 3.3 ml/sec 30 seconds 101-105 ml 3.5 ml/sec 30 seconds 106-110 ml 3.6 ml/sec 30 seconds 111-115 ml 3.8 ml/sec 30 seconds 116-120 ml 4.0 ml/sec 35 seconds 136-140 ml 4.6 ml/sec 30 seconds 141-145 ml 4.8 ml/sec 30 seconds 146-150mL 5.0 ml/sec 30 seconds 175 ml 5.8 ml/sec 30 seconds 180 ml 6.0 ml/sec 30 seconds 185 ml 6.0 ml/sec 31 seconds 200 ml 6.0 ml/sec 33 seconds
Contrast Injection Rate Body CT (excluding CTAs) Select Injection Rate All contrast agents If IV cannot accept > 2.0 ml/sec Injection Volume Injection Rate Injection Duration 46-50 ml 1.6 ml/sec 30 seconds 51-55 ml 1.8 ml/sec 30 seconds 56-60 ml 2.0 ml/sec 30 seconds 61-65 ml 2.0 ml/sec 32 seconds 66-70 ml 2.0 ml/sec 35 seconds 71-75 ml 2.0 ml/sec 37 seconds 76-80 ml 2.0 ml/sec 40 seconds 81-85 ml 2.0 ml/sec 42 seconds 86-90 ml 2.0 ml/sec 45 seconds 91-95 ml 2.0 ml/sec 47 seconds 96-100 ml 2.0 ml/sec 50 seconds 101-105 ml 2.0 ml/sec 52 seconds 106-110 ml 2.0 ml/sec 55 seconds 111-115 ml 2.0 ml/sec 57 seconds 116-120 ml 2.0 ml/sec 60 seconds 136-140 ml 2.0 ml/sec 70 seconds 141-145 ml 2.0 ml/sec 72 seconds 146-150mL 2.0 ml/sec 75 seconds 175 ml 2.0 ml/sec 87 seconds 180 ml 2.0 ml/sec 90 seconds 185 ml 2.0 ml/sec 92 seconds 200 ml 2.0 ml/sec 100 seconds
Body CT (excluding CTAs) Select Scanning Delay Routine Scans All scanners All delays from the beginning of injection Portal phase routine scan Injection Duration 30 seconds 31 seconds 32 seconds 33 seconds 35 seconds 37 seconds 40 seconds 42 seconds 45 seconds 47 seconds 50 seconds 52 seconds 55 seconds 57 seconds 60 seconds 70 seconds 72 seconds 75 seconds 87 seconds 90 seconds 92 seconds 100 seconds Delay 70 seconds 71 seconds 72 seconds 73 seconds 75 seconds 77 seconds 80 seconds 82 seconds 85 seconds 87 seconds 90 seconds 92 seconds 95 seconds 97 seconds 100 seconds 110 seconds 112 seconds 115 seconds 127 seconds 130 seconds 131 seconds 140 seconds
Implementing Algorithm Loose leaf handbooks (cookbooks) created One customized cookbook placed at each scanner Each cookbook is specific for scanner type and concentration of contrast material used Master reference cookbooks placed in radiology reading room
Liver Four-Phase (Abdomen or Abdomen/Pelvis): 40-slice, 64-slice Indications: Cirrhosis: evaluating for HCC and portal hypertension. Pre-Intervention planning: for TIPS, chemoembolization, embolization, ablation. Cholangiocarcinoma. Characterize unknown liver lesion. Notes, modifications: Should be done on 40 or 64-slice scanners, if possible, because 3D rendering is usually needed and these provide better image quality Pelvis should be performed if concern about pelvic metastasis or if known prior important pelvic abnormality If following up vascular metastases that are known to be seen best on portal venous phase, perform routine abdomen protocol. Contrast Unenhanced Phase (UP) Hepatic Arterial Phase (HAP) Portal Venous Phase (PVP) Delayed Phase (DP) Comments Oral contrast No No Rectal contrast No No IV contrast Š iodine conc. (mgi/ml) 350-370 Iodine dose (gi), Volume and Flow Rate 52 gi for 60-90 kg patient. Adjust proportionally for weight. See "Contrast Cookbook" This is a higher dose than routine protocols to optimize postprocessing and segmentation Saline flush - volume (ml) 50 If no dual injector, increase contrast dose by 10 ml Saline flush - flow rate (ml/s) Same as contrast injection rate Scan delay Trigger at 150 HU in aorta plus 15 seconds 45 seconds post-trigger 3 minutes post-trigger HAP slightly later than routine AP. Change delay to 10 minute for cholangiocarcinoma Acquisition Parameters Scout PA Lateral scanogram can help see spinal compressions; post-scan scanogram serves as a one-shot IVP Patient position Supine, feet first Supine, feet first Supine, feet first Supine, feet first Scan range Diaphragm to iliac crest Diaphragm to iliac crest Diaphragm to iliac crest or greater trochanter Liver Scanning direction Out Out Out Out Acquisition field of view Full patient width Full patient width Full patient width Full patient width Tube voltage (kvp) 120 120 120 120 Can use 140 kvp for large patients Tube load (mas) 170 to 200 250 to 300 250 to 300 170 to 200 Consider automated dose modulation Gantry rotation time (s) 0.5 0.5 0.5 0.5 Consider 0.75 for obese patients Detector configuration (mm) 40 x 0.625 or 64 x 0.625 40 x 0.625 or 64 x 0.625 40 x 0.625 or 64 x 0.625 32 x 1.25 or 64 x 0.625 Pitch 1 1 1 1 Reconstruction Parameters Axial reconstruction (mm) 5.0 x 5.0 5.0 x 5.0 5.0 x 5.0 5.0 x 5.0 Thin section axial for 3D/MPR (mm) 1.3 x 0.7 up to 2.0 x 1.0 1.3 x 0.7 up to 2.0 x 1.0 Coronal reconstruction (mm) 3.0 Š 4.0 x 3.0 3.0 Š 4.0 x 3.0 Recon filter kernel B or C B or C B or C Recon field of view Evolving Evolving Evolving Scanner automatically assigns optimal pitch based on approximate selection. Coronal and sagittal reconstructions should be performed routinely on HAP and PVP. Thick slab MIPs and/or sagittal MIPs may replace coronal and sagittal MPRs. Filter A helpful for very obese patients (less noisy images). Filter B if lower mas chosen (more noise than Filter A, but appropriate for average patient). Filter C increases spatial resolution, but also increases noise.
Pancreas (Abdomen or Abdomen/Pelvis): 40-slice, 64-slice Indications: Pancreatic mass known or suspected. Pancreatic carcinoma follow-up after treatment (surgery, XRT, chemotherapy) if pancreatic phase needed (see Exclusions, Notes below). Painless jaundice. Chronic pancreatitis vs. pancreatic mass. Acute pancreatitis > age 50 to rule out mass as etiology of pancreatitis. Exclusions: Acute pancreatitis < age 50 (Routine protocol). Known chronic pancreatitis to evaluate complications (Routine protocol). Known pancreatic adenocarcinoma recurrence or metastasis if well seen on PVP (Routine protocol). Pancreatic neuroendocrine tumor follow-up after treatment (RCC, Vascular Cancer FU protocol). Notes, modifications: Should be done on 40 or 64-slice scanners, if possible, because 3D rendering is usually needed and these provide better image quality. Pelvis should be performed if concern about pelvic metastasis or if known prior important pelvic abnormality. If following known unresectable pancreatic carcinoma, including with metastases, a routine abdomen or abdomen/pelvis may suffice. Routine examination may also be done for chronic pancreatitis to evaluate complications, acute pancreatitis < age 50, or pancreatitis reassessment. Contrast Unenhanced Phase (UP) Pancreatic Phase (PP) Portal Venous Phase (PVP) Comments Water or Volumen TM 500 ml to tolerance plus 250 ml Oral contrast water on table Rectal contrast No IV contrast Š iodine conc. (mgi/ml) 350-370 Iodine dose (gi), Volume and Flow Rate 52 gi for 60-90 kg patient. Adjust proportionally for weight. See "Contrast Cookbook" Saline flush - volume (ml) 30 Saline flush - flow rate (ml/s) Same as contrast injection rate Trigger at 150 HU in aorta plus 15 Scan delay seconds Acquisition Parameters 50 seconds post-trigger Scout PA Patient position Supine, feet first Supine, feet first Supine, feet first Diaphragm to iliac crest or greater Scan range Diaphragm to iliac crest Diaphragm to iliac crest trochanter Scanning direction Out Out Out Acquisition field of view Full patient width Full patient width Full patient width This is a higher dose than routine protocols to optimize post-processing and segmentation. Prefer higher injection rate, if possible, up to 5 ml/sec. If no dual injector, increase contrast dose by 10 ml Lateral scanogram can help see spinal compressions; post-scan scanogram serves as a one-shot IVP Tube voltage (kvp) 120 120 120 Can use 140 kvp for large patients Tube load (mas) 170 to 200 250 to 300 250 to 300 Consider automated dose modulation Gantry rotation time (s) 0.5 0.5 0.5 Consider 0.75 for obese patients Detector configuration (mm) 40 x 0.625 or 64 x 0.625 40 x 0.625 or 64 x 0.625 40 x 0.625 or 64 x 0.625 Pitch 1 1 1 Reconstruction Parameters Axial reconstruction (mm) 5.0 x 5.0 2.0 x 2.0 4.0 x 3.0 Thin section axial for 3D/MPR (mm) 1.3 x 0.7 up to 2.0 x 1.0 1.3 x 0.7 up to 2.0 x 1.0 Coronal reconstruction (mm) 3.0 Š 4.0 x 3.0 3.0 Š 4.0 x 3.0 Recon filter kernel B or C B or C Recon field of view Evolving Evolving Scanner automatically assigns optimal pitch based on approximate selection. Perform 3D volume and curved planar reformatting. Note: qualifies for additional postprocessing coding Coronal reconstructions should be performed on both the Pancreatic and Portal Venous phases. Thick slab MIPs and/or sagittal MIPs may be considered as a replacement for coronal and sagittal MPRs. Filter A helpful for very obese patients. Filter B if lower mas chosen
Renal Mass Pre-Intervention
Renal Mass Pre-intervention Indications: Prepare for nephron-sparing surgery or ablation Objectives: Define detailed vascular supply Localization Staging
Scan Phases Non-contrast May delete if have had recent non-contrast Arterial Through mid-pelvis to assure ID of anomalous arteries Nephrographic/excretory Entire abdomen-pelvis Split-dose
Split-Dose Injection Permits multiple purposes in single series, e.g. Late corticomedullary-early nephrographic Nephrographic-excretory
Split-Dose Injection Purpose Combine advantages of excretory, nephrographic and portal venous phases Use for both renal mass pre-intervention and CT urography protocols Renal mass includes arterial phase CT urography does not
Split-Dose Protocol Example Example: 115 ml Isovue 370 selected for 70 kg patient Inject about 1/4 of usual dose (30 ml) by hand Wait 10 minutes for excretion 300 ml saline IV during pause Inject additional complete dose (115 ml @ 4 ml/sec) Arterial phase Scan delay of 100 sec (for nephrographic phase)
Split-Dose Injection Nephrographic-Excretory Late CM-Arterial-Excretory
Renal Mass Visualization Lesion margins seen better on nephrographic phase
Post-Processing - MIPS Nephrographic/Excretory depicts vascular-collecting system to lesion relationships
Split-Dose Injection Arterial-Nephrographic Nephrographic-Excretory
Summary CT technology and protocol design is extremely complex. First step to tailoring exams is to understand basic principles of contrast dynamics and CT technology.