Actually, I use $my_plugin_settings = get_option('my_plugin_settings');

I explain again my problem, because I think there is a misunderstanding:

My plugin was working without any trouble until the last version of Piklist. My problem is not how to load data, my problem is that the new version of Piklist is now returning an array instead of a string for radio fields.

With version 0.9.3.6:
var_dump( $my_plugin_settings['a_radio_field'] )
returns
string(4) "grid"

With version 0.9.4 (and version 0.9.4.1):
var_dump( $my_plugin_settings['a_radio_field'] )
returns
array(1) { [0]=> string(4) "grid" }

Here my radio field code:

<?php
/*
Title: My Plugin
Setting: my_plugin_settings
Tab Order: 10
*/

piklist('field', array(
	'type' => 'radio'
	,'field' => 'display_type'
	,'label' => 'List display'
	,'value' => 'grid'
	,'choices' => array(
		'grid' => 'Grid'
		,'list' => 'List'
		,'quicksand' => 'jQuery Quicksand'
	)
));

And I use somewhere else in my plugin this variable to call the value:
$my_plugin_settings['display_type']

This variable was returning a string before the update, like 'grid', 'list' or 'quicksand'.
Now I get an array, like array { [0]=> "list" }

Thank you