Frank P. Dawry Physx.home.comcast.net Ventilation/Perfusion (V/Q) Imaging

Frank P. Dawry Physx.home.comcast.net Ventilation Imaging Bronchi Bronchioles Alveoli Air flow through the bronchial system

Frank P. Dawry Physx.home.comcast.net Perfusion Imaging Blood flow through the pulmonary arterial system Based upon the trapping of large (>10 µm) particles in the capillary bed of the lungs.

Frank P. Dawry Physx.home.comcast.net Ventilation-Perfusion Imaging Ventilation Airway patency Airway obstruction EmphysemaBronchitisPerfusion Pulmonary embolism Tumor Tuberculosis Fibrosis infection

Frank P. Dawry Physx.home.comcast.net Ventilation / Perfusion Ventilation – usually performed prior to perfusion Xenon-133 T1/2 = 5.3 days 80 keV Posterior – seated 10 to 20 mCi in re-breathing apparatus Equilibrium image followed by a washout – one view Krypton-81m T1/2 = 13 seconds 190 keV Constant inhalation Wash in only Tc99m-labeled aerosol T1/2 = 6.0 hours 140 keV ~35 mCi in nebulizer – 10% actual lung dose delivered The aerosol is administered through a mouthpiece with the nose occluded and the patient performing tidal breathing. Perfusion appearance Technegas / Pertechnegas Not yet available in the United States Fullerenes (Bucky Balls)

Frank P. Dawry Physx.home.comcast.net Ventilation / Perfusion Perfusion – follows ventilation Tc-99m MAA (Macro aggregated albumin) 2-6 mCi larger activity than used in Aerosol imaging 4 x greater count rate compared to ventilation because both use Tc-99m Patient usually injected slowly in supine position, taking deep breaths / imaged upright 500k – 1000k counts/view particles administered –Adults 200,000–700,000 particles –Pediatrics Neonates – 10,000 particles Neonates – 10,000 particles < 5 years old – 50,000 to 150,000 particles < 5 years old – 50,000 to 150,000 particles –Patients with pneumonectomy and severe hypertension – 100,000 to 250,000 particles

Frank P. Dawry Physx.home.comcast.net Ventilation / Perfusion Pulmonary artery progressively narrows through about 22 branchings until the terminal pulmonary arteriole branches into many (~35 micron) pre-capillary units. There are almost 3E11 units in the lung and the usual scan dose will block about one in every 10,000.

Frank P. Dawry Physx.home.comcast.net Ventilation / Perfusion Incredibly safe – but dose should be injected slowly to be sure – patient may have impaired vascular tree due to extensive disease, e.g. adenocarcinoma occluding large amounts of the vascular tree, or profound vascular disease.

Frank P. Dawry Physx.home.comcast.net When using 99m Tc for both the Ventilation (aerosol) and the Perfusion (MAA), it is extremely important that the count rate of the second study is at least three to four times the count rate of the first study. Ventilation count rate ≈ 2,000- counts/second Perfusion count rate ≈ 11,000- counts/second

Frank P. Dawry Physx.home.comcast.net The number of particles available per dose of Tc-99m MAA will vary depending on the physical decay that has occurred. The number of particles in any dose and volume to be administered may be calculated as follows: Assume the average number of particles per vial = 6.0 x If: V = volume to be administered in ml V A = volume to be administered in ml D = desired dose to be administered (mCi) C = concentration of Tc-99m to be added to the reaction vial. (mCi/ml) Fr = fraction of Tc-99m remaining after the time of calibration – taken from decay factor chart P = number of particles in dose to be administered V = volume of solution added to reaction vial V TC = volume of solution added to reaction vialThen: V = __D __ and P = _Va_ x 6.0 x 10 6 V A = __D __ and P = _Va_ x 6.0 x 10 6 C X Fr V TC C X Fr V TC

Frank P. Dawry Physx.home.comcast.net Lung Perfusion particle calculations Determine the volume dose to be administered to the patient: specific concentration = activity/volume required volume = activity desired/specific concentration or ml = mCi / mCi/ml Calculate the particle concentration of the reconstituted kit: total particles in kit/ml added to kit = particles/ml Calculate the particles per dose: particles/1.0 ml = particles in patient dose/ml of patient dose (particle concentration in particles/ml)(ml dose volume) = particles in patient dose

Particle number determination Time = 12:00 (T=0) Add 1.3 ml 99m Tc (30 mCi ) to vial Add 3.7 ml of saline =30 mCi/5.0 ml =6 mCi/ml  Inject 0.7 ml = 4 mCi = 840,000 particles ! 6,000,000/5ml = x/0.7ml X = 840,000  Inject 0.5 ml = 3 mCi = 600,000 particles 6,000,000/5ml = x/0.5ml X = 600,000Have: 30 mCi 99m Tc in 1.3 ml Calibration time = 12:00 Wanted Dose: 200, 000 – 700,000 particles 3 – 5 millicuries Given: MAA Vial contains 6 x 10 6 particles (6 million) Frank P. Dawry Physx.home.comcast.net

Particle number determination more dilute Have: 30 mCi 99m Tc in 1.3 ml Calibration time = 12:00 Wanted Dose: 200, 000 – 700,000 particles 3 – 5 millicuries Given: MAA Vial contains 6 x 10 6 particles (6 million) Time = 12:00 (T=0) Add 1.3 ml 99m Tc (30 mCi ) to vial Add 5.7 ml of saline =30 mCi/7.0 ml =4.3 mCi/ml  Inject 0.9 ml = 3.9 mCi = 1,080,000 particles !! 6,000,000/7ml = x/0.9ml X = 1,080,000 more dilute = more particles injected Frank P. Dawry Physx.home.comcast.net

Particle number determination more concentrated Have: 30 mCi 99m Tc in 1.3 ml Calibration time = 12:00 Wanted Dose: 200, 000 – 700,000 particles 3 – 5 millicuries Given: MAA Vial contains 6 x 10 6 particles (6 million) Time = 12:00 (T=0) Add 1.3 ml 99m Tc (30 mCi ) to vial Add 2.7 ml of saline =30 mCi/4.0 ml =7.5 mCi/ml  Inject 0.5 ml = 3.75 mCi = 400,000 particles ☺ 6,000,000/7.5ml = x/0.5ml X = 400,000 more concentrated = less particles injected Frank P. Dawry Physx.home.comcast.net

Particle number determination High specific activity Have: 30 mCi 99m Tc in 1.3 ml Calibration time = 12:00 Wanted Dose: 200, 000 – 700,000 particles 3 – 5 millicuries Given: MAA Vial contains 6 x 10 6 particles (6 million) Time = 06:00 (T= 6 hours early) Add 1.3 ml 99m Tc (60 mCi ) to vial Add 3.7 ml of saline =60 mCi/5.0 ml =12 mCi/ml  Inject 0.3 ml = 3.6 mCi = 360,000 particles ☺ 6,000,000/5ml = x/0.3ml X = 360,000 more concentrated = less particles injected Frank P. Dawry Physx.home.comcast.net

Particle number determination Low specific activity Have: 30 mCi 99m Tc in 1.3 ml Calibration time = 12:00 Wanted Dose: 200, 000 – 700,000 particles 3 – 5 millicuries Given: MAA Vial contains 6 x 10 6 particles (6 million) Time = 18:00 (T= 6 hours later) Add 1.3 ml 99m Tc (15 mCi ) to vial Add 3.7 ml of saline =15 mCi/5.0 ml =3 mCi/ml  Inject 1.3 ml = 3.9 mCi = 1,560,000 particles !! 6,000,000/5ml = x/1.3ml X = 1,560,000 more dilute = more particles injected Frank P. Dawry Physx.home.comcast.net

Particle number determination Rule of Thumb Never draw greater than 1.0 ml into injection syringe. Prepare a fresh vial of MAA instead. Consider reconstituting vial with 5.0 ml saline and discarding 2.5 ml, then add the low specific activity 99mTc Calculations now based upon 3,000,000 particles in the vial of MAA Frank P. Dawry Physx.home.comcast.net

Physx.home.comcast.net Perfusion segments

Frank P. Dawry Physx.home.comcast.net Ventilation segments

Frank P. Dawry Physx.home.comcast.net Quantitation of Perfusion