patient preparation and coronary cta techniques

Patient preparation and coronary CTA techniques

Gregory Kicska, M.D. Ph.D.University of Washington, Thoracic Imaging

Overview

1. Patient preparation2. Scanning techniques

Patient preparation

Preparation related to any contrast CT examination

Preparation specific to coronary CTA

Exclude contraindications

Patient safety

Study quality

Contrast

renal insufficiency

allergy (anaphylaxis)

Radiation

pregnancy

radiation dose/age

Claustrophobia

Medically unstable

Contraindications: patient saftey

Contrast

renal insufficiencycreatinine measurement before intravenous contrast mediainjection are summarized in Table 4. Most centers employ aserum creatinine threshold of 1.5 mg/dl for detection ofpatients at high risk for contrast-induced nephrotoxicity.However, considerable derangement of renal function canbe masked by a normal appearing serum creatinine report.Hence, the current recommendation is to screen high-riskpatients with estimated glomerular filtration rate (GFR).Derangement of GFR can occur in a patient due toundetected chronic renal disease though the creatininemeasurements are normal. The Modification of Diet inRenal Disease (MDRD) study group equation is anaccurate method for GFR estimation from serum creatinine[27]:

GFR !186" serum creatinine# $% 1:154" age# $ % 0:203" k

For women, k=0.742; for men, k=1Multiply by 1.210 if African-AmericanThe risk of contrast-induced nephrotoxicity based on

estimated GFR is summarized in Table 5. Recently, somevendors are investigating rapid strip-test-based methods forquick measurement of serum creatinine when patients arrivefor contrast-enhanced radiological studies [28]. Such methodsto estimate serum creatinine can enable efficient detection ofpatients at risk for contrast-induced nephrotoxicity.

Metformin therapy and the risk of lactic acidosis

When patients taking metformin receive iodinated contrastmedia, they are at risk for lactic acidosis. If renaldysfunction occurs due to iodinated contrast media, anaccumulation of metformin can occur and cause lacticacidosis. According to the American College of Radiology(ACR) guidelines, metformin should be discontinued at thetime of an examination or procedure using intravascularcontrast media, withheld for 48 h after the procedure, andreinstated only after renal function has been re-evaluatedand found to be normal [3]. However, the examination mayproceed even if the patient took a dose of metformin on themorning of the examination.

Administration of contrast media to pregnant patients andnursing mothers

When given in usual clinical doses, iodinated contrastmedia cross the human placenta and enter the fetus [3]. Noadequate and well-controlled teratogenic studies of theeffects of these agents in pregnant women have beenperformed. While it is not possible to conclude thatiodinated contrast media present a definite risk to the fetus,there is insufficient evidence to conclude that they pose norisk. The ACR recommends that iodinated contrast mediamay be given to pregnant patients only when [3]:

– the diagnostic information requested using contrast-enhanced study cannot be obtained via other means(such as ultrasound)

– the information needed affects the care of the patientand fetus during the pregnancy

– it is not prudent to wait to obtain this information untilafter the patient is no longer pregnant

Less than 1% of iodinated contrast media is excreted intobreast milk, out of which only 1% is absorbed by theinfant’s gut. According to ACR recommendations, it is safefor the mother and infant to continue breast-feeding afterreceiving contrast media [3]. However, if the motherremains concerned about any potential ill effects to theinfant, she may abstain from breast-feeding for 24 h [3].

Conclusion

Prompt recognition and treatment are invaluable inblunting an adverse response of a patient to contrastmedia, and may prevent a reaction from becoming severeor even life-threatening. Proper patient evaluation andprocedure selection, and adequate prophylactic measurescan prevent some adverse reactions. Knowledge, training,and preparation are crucial for appropriate and effectivetherapy in the event of an adverse reaction. Radiologistsand their staff need to review the treatment algorithmsregularly so that each can accomplish his or her roleefficiently.

Table 4 Indications for serum creatinine measurement beforeintravenous administration of iodinated contrast media

History of kidney diseaseFamily history of renal failureDiabetes treated with insulin or other medications prescribed by aphysicianMyelomaCollagen vascular diseaseMedications: metformin, non-steroidal anti-inflammatory drugs,aminoglycosides

Table 5 Risk of contrast induced nephrotoxicity based on estimatedglomerular filtration rate (GFR)

GFR (ml/min/1.73 m2)

Risk of contrast inducednephrotoxicity

Intravenous iodinatedcontrast media

60 Negligible Safe30–60 Moderate Use only if clinically

essential prophylaxisrequired

<30 High Contraindicated

214


Contrast

renal insufficiency

creatinine measurement before intravenous contrast mediainjection are summarized in Table 4. Most centers employ aserum creatinine threshold of 1.5 mg/dl for detection ofpatients at high risk for contrast-induced nephrotoxicity.However, considerable derangement of renal function canbe masked by a normal appearing serum creatinine report.Hence, the current recommendation is to screen high-riskpatients with estimated glomerular filtration rate (GFR).Derangement of GFR can occur in a patient due toundetected chronic renal disease though the creatininemeasurements are normal. The Modification of Diet inRenal Disease (MDRD) study group equation is anaccurate method for GFR estimation from serum creatinine[27]:

GFR !186" serum creatinine# $% 1:154" age# $ % 0:203" k

For women, k=0.742; for men, k=1Multiply by 1.210 if African-AmericanThe risk of contrast-induced nephrotoxicity based on

estimated GFR is summarized in Table 5. Recently, somevendors are investigating rapid strip-test-based methods forquick measurement of serum creatinine when patients arrivefor contrast-enhanced radiological studies [28]. Such methodsto estimate serum creatinine can enable efficient detection ofpatients at risk for contrast-induced nephrotoxicity.

Metformin therapy and the risk of lactic acidosis

When patients taking metformin receive iodinated contrastmedia, they are at risk for lactic acidosis. If renaldysfunction occurs due to iodinated contrast media, anaccumulation of metformin can occur and cause lacticacidosis. According to the American College of Radiology(ACR) guidelines, metformin should be discontinued at thetime of an examination or procedure using intravascularcontrast media, withheld for 48 h after the procedure, andreinstated only after renal function has been re-evaluatedand found to be normal [3]. However, the examination mayproceed even if the patient took a dose of metformin on themorning of the examination.

Administration of contrast media to pregnant patients andnursing mothers

When given in usual clinical doses, iodinated contrastmedia cross the human placenta and enter the fetus [3]. Noadequate and well-controlled teratogenic studies of theeffects of these agents in pregnant women have beenperformed. While it is not possible to conclude thatiodinated contrast media present a definite risk to the fetus,there is insufficient evidence to conclude that they pose norisk. The ACR recommends that iodinated contrast mediamay be given to pregnant patients only when [3]:

– the diagnostic information requested using contrast-enhanced study cannot be obtained via other means(such as ultrasound)

– the information needed affects the care of the patientand fetus during the pregnancy

– it is not prudent to wait to obtain this information untilafter the patient is no longer pregnant

Less than 1% of iodinated contrast media is excreted intobreast milk, out of which only 1% is absorbed by theinfant’s gut. According to ACR recommendations, it is safefor the mother and infant to continue breast-feeding afterreceiving contrast media [3]. However, if the motherremains concerned about any potential ill effects to theinfant, she may abstain from breast-feeding for 24 h [3].

Conclusion

Prompt recognition and treatment are invaluable inblunting an adverse response of a patient to contrastmedia, and may prevent a reaction from becoming severeor even life-threatening. Proper patient evaluation andprocedure selection, and adequate prophylactic measurescan prevent some adverse reactions. Knowledge, training,and preparation are crucial for appropriate and effectivetherapy in the event of an adverse reaction. Radiologistsand their staff need to review the treatment algorithmsregularly so that each can accomplish his or her roleefficiently.

Table 4 Indications for serum creatinine measurement beforeintravenous administration of iodinated contrast media

History of kidney diseaseFamily history of renal failureDiabetes treated with insulin or other medications prescribed by aphysicianMyelomaCollagen vascular diseaseMedications: metformin, non-steroidal anti-inflammatory drugs,aminoglycosides

Table 5 Risk of contrast induced nephrotoxicity based on estimatedglomerular filtration rate (GFR)

GFR (ml/min/1.73 m2)

Risk of contrast inducednephrotoxicity

Intravenous iodinatedcontrast media

60 Negligible Safe30–60 Moderate Use only if clinically

essential prophylaxisrequired

<30 High Contraindicated

214Contraindications: patient saftey

Radiation

pregnancy

radiation dose/age


Claustrophobia

Diazapam 5 mg oral*

Medically unstable

*Dose adjustment needed specific conditions


Contraindications: study qualityMotion

Breath hold

Gating

Artifact

Inability to raise arms

Metal

Obesity


Breath hold (7-12 sec @ 64 slice)

270 ms acquisition dual source


Gating

atrial fibrillation or frequent PVCs

Contraindications: study quality Artifact

Inability to raise arms

Metal

Obesity

The ideal patient

HR < 65, sinus

Calm

Thin

Large veins

Pearl diver (able to hold breath)

Able to follow commands

No caffeine (24 hrs)No viagra (24 hrs)No “energy supplement” (24 hrs)No food (4 hrs)No liquid (1 hr)

Preparation: 24-1 hr pre-exam

Cardiac medications should not be suspended!


Non-anaphylactic contrast reaction•50 mg prednisone @ 13,7,1 hrs before exam

•oral Benadryl 1 hour before exam


•IV access•18 - 20 gauge needle•Right arm

Preparation: 1 hr pre-exam

Satisfactory IV accessContraindications excluded / mitigated


Proceed to HR control

Contraindications Metoprolol allergy

Bronchospastic disease (asthma)Aortic valve disease

Worsening heart failureHeart block

Oral metoprolol (50 mg tabs)50-100 mgWait 90 minutes, check BP/HRConsider additional 50 mg

IV metoprolol (5 mg)Give 5 mg IVPWait 20 minutes, check BP/HRConsider additional 5 mg x 2



Beta blocker contraindication? Consider oral Verapamil

HR < 65 bpm


Proceed to Ca++ score

Center heart in scanner

Examination: patient positioning

Center heart in scanner

Examination: patient positioning

= Lowest noise

Ca++ score coverage

Examination: Ca++ score

Examination: Ca++ scoreVoxels are 3 x 1.3 x 1.3 mmnon-overlapping

Threshold of 130 H.U.

Agatston volumemass score

> 400-1000 - high risk of stenosis= 0 - CAD unlikely

Ca++ Score Sensitivity Specificity

>1

>100

>1000

92% 75%

73% 90%

30% 98%

Predicting Stenosis

Low false negative

No false positiveLow sensitivity on CTA

Examination: Ca++ score

Examination: Ca++ score0 < Agatston score < 400-1000

Proceed to CTA planning

Retrospective, dose modulation

Retrospectiveno modulation

Retrospectivewith modulation

Prospective

Old - HR 92, BP 110/60, Weight 260 lbs,Temp 37

New - HR 80, BP 98/60

Examination: gating

Retrospective, dose modulation

Retrospectiveno modulation

Retrospectivewith modulation

Prospective

Old - HR 92, BP 110/60, Weight 260 lbs,Temp 37

New - HR 80, BP 98/60

Prospective RetrospectiveModulation

Rate < 70no functionno calciumAge < 40

Rate > 70functioncalcium

Age > 40

RetrospectiveNo modulation

A-fib

Ca++ score coverage

Examination: CTA coverage

Top slice with CA

Bottom slice with CA

Coronary CTA coverage (retrospective)

Ca++ score coverage

Examination: CTA coverage

Top slice with CA

Bottom slice with CA

Coronary CTA coverage (prospective)

Set kVp and MAS.

Automatic exposure control

set desired held soon in its standard deviation

set upper and lower limits to avoid spikes in current due to hardware

Weight table

Examination: dose

Examination: dose

Examination: dose

Participate in dose related QA

80 ml5 ml/s

40 ml4 ml/s

50 ml4 ml/s

100%60%

100%40%

Examination: contrast

ContraindicationsHead trauma/bleedSystolic BP < 100Nitrate AllergyPhosphodiesterase inhibitors

AdverseHeadaches - 50%

Examination: nitroglycerin

4 minutesExamination: nitroglycerin

4 minutes elapsed

Proceed to CTA scanning

Examination: nitroglycerin

Examination: scanning

Examination: reconstruction

Main reconstruction for 3D station

Thin section (0.625 mm) axial cardiac kernal< 32cm FOV50% overlap

Examination: reconstruction

Additional reconstruction for 2D station

•Axial 2.5 mm, lung kernel, lung FOV•Axial 2.5 mm, body kernel, body FOV•Coronal/sagittal, body kernel

Conclusions

• Exclude contraindications related to patient safety or exam quality• ensure proper patient preparation for contrast exam• control heart rate with beta blocker• calcium scoring is used to plan CTA or terminate exam• scanner gating is one of the most effective ways to reduce dose• utilize automatic exposure control when possible

Thank you

patient preparation and coronary cta techniques

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