Acoustic radiation force imaging

A method of operating a medical apparatus, wherein the medical apparatus comprises a high intensity focused ultrasound system for sonicating a sonication region, wherein the medical apparatus further comprises a magnetic resonance imaging system for acquiring magnetic resonance data from an imaging zone, wherein the sonication region and the imaging zone at least partially overlap, wherein the method comprises the steps of:

• acquiring first magnetic resonance data by controlling the magnetic resonance imaging system with pulse sequence commands and by controlling the high intensity focused ultrasound system with first sonication commands, wherein the pulse sequence commands control the magnetic resonance imaging system to acquire magnetic resonance data according to an acoustic radiation force imaging protocol, wherein the pulse sequence specifies the acquisition of the magnetic resonance data for multiple pulse sequence repetitions, wherein the pulse sequence commands specify for each of the multiple sequence repetitions a first group of motion encoding gradients and a second group of motion encoding gradients, the first and second group of motion encoding gradients are applied with the same polarity and wherein the first sonication commands cause the high intensity focused ultrasound system to sonicate the sonication region during the first group of motion encoding gradients according to the acoustic radiation force imaging protocol;
• acquiring second magnetic resonance data by controlling the magnetic resonance imaging system with the pulse sequence commands and by controlling the high intensity focused ultrasound system with the second sonication commands, wherein the second sonication commands cause the high intensity focused ultrasound system to sonicate the sonication region during the second group of motion encoding gradients according to the acoustic radiation force imaging protocol;
• apply different trigger delays to the first and second sonication commands
• reconstructing a first motion encoded image from the first magnetic resonance data;
• reconstructing a second motion encoded image from the second magnetic resonance data;
• and
• constructing a displacement map from the difference of the first motion encoded image and the second motion encoded image.

A computer program product for execution by a processor controlling a medical apparatus, wherein the medical apparatus comprises:

• a high intensity focused ultrasound system for sonicating a sonication region, wherein the medical apparatus further comprises a magnetic resonance imaging system for acquiring magnetic resonance data from an imaging zone, wherein the sonication region and the imaging zone at least partially overlap, wherein execution of the machine executable instructions causes the processor to:
• acquire first magnetic resonance data by controlling the magnetic resonance imaging system with pulse sequence commands and by controlling the high intensity focused ultrasound system with first sonication commands, wherein the pulse sequence commands cause the magnetic resonance imaging system to acquire the first magnetic resonance data according to an acoustic radiation force imaging protocol, wherein the pulse sequence commands specify the acquisition of the magnetic resonance data for multiple pulse sequence repetitions, wherein the pulse sequence commands specifies for each of the multiple pulse sequence repetitions a first group of motion encoding gradients and a second group of motion encoding gradients, the first and second group of motion encoding gradients are applied with the same polarity and wherein the first sonication commands cause the high intensity focused ultrasound system to sonicate the sonication region during the first group of motion encoding gradients according to the acoustic radiation force imaging protocol;
• acquire second magnetic resonance data by controlling the magnetic resonance imaging system with the pulse sequence commands and by controlling the high intensity focused ultrasound system with the second sonication commands, wherein the second sonication commands cause the high intensity focused ultrasound system to sonicate the sonication region during the second group of motion encoding gradients according to the acoustic radiation force imaging protocol;
• apply different trigger delays to the first and second sonication commands
• reconstruct a first motion encoded image from the first magnetic resonance data;
• reconstruct a second motion encoded image from the second magnetic resonance data;
• and
• construct a displacement map from the difference of the first motion encoded image and the second motion encoded image.